Internetworking Technology Overview

CISC SYS TEMS nternetworking Technoogy Overview

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About This Manual xxi

Document Objectives xxi

Audience xxi

Document Organization xxi

Document Conventions xxii

PART Interuetworking Basics

Chapter Introduction to Internetworking 1-1

Introduction 1-1

OSI Reference Model Introduction 1-1

Hierarchical Communication 1-1

Information Formats 1-3

Compatibility Issues 1-4

OSI Layers 1-4

Application Layer 1-4 Presentation Layer 1-4 Session Layer 1-4

Transport Layer 1-5

Network Layer 1-5 Link Layer 1-5

Physical Layer 1-5

Important Terms and Concepts 1-5

Addressing 1-5

Frames Packets and Messages 1-6

Key Organizations 1-6

Chapter Routing Basics 2-1

Background 2-1

Routing Components 2-1

Path Determination 2-1

Switching 2-2

Routing Algorithms 2-3

Design Goals 2-4

Optimality 2-4

Simplicity 2-4

Robustness 2-4

Rapid Convergence 2-4

Flexibility 2-5

Types 2-5

Static or Dynamic 2-5

Single-Path or Multipath 2-6

Flat or Hierarchical 2-6

Table of Contents Host-Intelligent or Router-Intelligent 2-6

Intradomain or Interdomain 2-6

Link State or Distance Vector 2-7

Metrics 2-7

Path Length 2-7

Reliability 2-7

Delay 2-8

Bandwidth 2-8

Load 2-8

Communication Cost 2-8

Routed vs Routing Protocols 2-8

Chapter Bridging Basics 3-1

Background 3-1

Internetworking Device Comparison 3-1

Technology Basics 3-2

Types of Bridges 3-3

Chapter Network Management Basics 4-1

Background 4-1

Network Management Architecture 4-1

The ISO Network Management Model 4-2 Performance Management 4-2

Configuration Management 4-3 Accounting Management 4-3 Fault Management 4-4

Security Management 4-4

PART Media-Access Technooges

Chapter Ethernet/IEEE 802.3 5-1

Background 5-1

Ethernet/IEEE 802.3 Comparison 5-1

Physical Connections 5-2

Frame Formats 5-3

Chapter Token Ring/IEEE 802.5 6-1

Background 6-1

Token Ring/IEEE 802.5 Comparison 6-1

Token Passing 6-2

vi Internetworking Technology Overview Physical Connections 6-3

Priority System 6-3

Fault Management Mechanisms 6-4

Frame Format 6-4

Tokens 6-4 Data/Command Frames 6-5

7-1 Chapter Fiber Distributed Data Interface

Background 7-1

Technology Basics 7-1

FDDI Specifications 7-2

Physical Connections 7-2

Traffic Types 7-3

Fault-Tolerant Features 7-4

Frame Format 7-6

Interface 8-i Chapter High-Speed Serial

Background 8-1

Technology Basics 8-1

9-1 Chapter Point-to-Point Protocol

Background 9-1

PPP Components 9-1

General Operation 9-2

Physical-Layer Requirements 9-2

The PPP Link Layer 9-2

The PPP Link Control Protocol 9-3

10-1 Chapter 10 Integrated Services Digital Network

Background 10-1

Components 10-1

Services 10-2

Layer 10-3

Layer2 10-4

Layer 10-4

Table of Contents vii Chapter 11 Synchronous Data Link Control and Derivatives 11-1

Background 11-I

Technology Basics 11-1

Frame Format 11-2

Derivative Protocols 11-4

HDLC 11-4

LAPB 11-5

IEEE 802.2 11-5

QLLC 11-6

PART Packet-Swftchhig Technoogies

Chapter 12 X.25 12-1

Background 12-1

Technology Basics 12-1

Frame Format 12-3

Layer 12-3 Layer 12-4 Layer 12-5

Chapter 13 Frame Relay 13-1

Background 13-1

Technology Basics 13-1

LMI Extensions 13-2

Frame Format 13-3

LMI Message Format 13-4

Global Addressing 13-5

Multicasting 13-6

Network Implementation 13-6

Chapter 14 Switched Multimegabit Data Service 14-1

Background 14-1

Technology Basics 14-1

Addressing 14-2

Access Classes 14-3

SMDS Interface Protocol SIP 14-3

CPE Configurations 14-4

SIP Levels 14-4

viii lnternetworking Technology Overview Level 14-5

Level2 14-6

Level 14-7

Network Implementation 14-8

Chapter 15 Asynchronous Transfer Mode 15-1

Background 15-1

Technology Basics 15-2

ATM Physical Layer 15-3 ATM Layer 15-3

ATM Adaptation Layers 15-5

AAL3/4 15-6

AAL5 15-7

ATM Architectures 15-8 ATM Permanent Virtual Connection PVC Service 15-9 ATM Switched Virtual Connection SVC Service 15-10 ATM Connectionless Service 15-11

PART Routed Protocols

Chapter 16 AppleTalk 16-1

Background 16-1

Technology Basics 16-1

Media Access 16-2

Network Layer 16-3

Protocol Address Assignment 16-3

Network Entities 16-4

Datagram Delivery Protocol DDP 16-5 Routing Table Maintenance Protocol RTMP 16-6

Transport Layer 16-7 AppleTalk Transaction Protocol ATP 16-7 AppleTalk Data Stream Protocol ADSP 16-7

Upper-Layer Protocols 16-8

Chapter 17 DECnet 11-1

Background 17-1

Digital Network Architecture DNA 17-1

Media Access 17-2

Network Layer 17-2 DECnet Phase IV Routing Frame Format 17-3

Addressing 17-4

Table of Contents ix Routing Levels 17-5

Transport Layer 17-6

Upper-Layer Protocols 17-6

Chapter 18 Internet Protocols 18-1

Background 18-1

Network Layer 18-2

Addressing 18-4

Internet Routing 18-6

ICMP 18-7

IRDP 18-7

Transport Layer 18-8 Transmission Control Protocol TCP 18-8 User Datagram Protocol UDP 18-9

Upper-Layer Protocols 18-9

Chapter 19 NetWare Protocols 19-1

Background 19-1

Technology Basics 19-1

Media Access 19-2

Network Layer 192

Transport Layer 19-4

Upper-Layer Protocols 19-4

Chapter 20 OSI Protocols 20-1

Background 20-1

Technology Basics 20-1

Media Access 20-1

Network Layer 20-2

Connectionless Service 20-2

Connection-Oriented Service 20-3

Addressing 20-3

Transport Layer 20-4

Upper-Layer Protocols 20-5 Session Layer 20-5

Presentation Layer 20-5 Application Layer 20-5

Internetworking Technology Overview Chapter 21 Banyan VINES 21-1

Background 21-1

Technology Basics 21-1

Media Access 21-2

Network Layer 21-2 VINES Internetwork Protocol VIP 21-2 Routing Table Protocol RTP 21-5 Address Resolution Protocol ARP 21-6 Internet Control Protocol ICP 21-6

Transport Layer 21-7

Upper-Layer Protocols 21-7

Chapter 22 Xerox Network Systems 22-1

Background 22-1

Technology Basics 22-1

Media Access 22-2

Network Layer 22-2

Transport Layer 22-4

Upper-Layer Protocols 22-4

PART Routing ProtocWs

Chapter 23 Routing Information Protocol 23-1

Background 23-1

Routing Table Format 23-1

Packet Format IP Implementations 23-2

Stability Features 23-3

Hop-Count Limit 23-3 Hold-Downs 23-4

Split Horizons 23-4

Poison Reverse Updates 23-4

Chapter 24 Interior Gateway Routing Protocol and Enhanced Interior Gateway Routing Protocol 24-1

Background 24-1

Technology 24-1

Stability Features 24-2

Hold-Downs 24-2

Split Horizons 24-2

Table of Contents xi Poison Reverse Updates 24-3 Timers 24-3

EIGRP 24-3

Compatibility with IGRP 24-4

EIGRP Technology 24-4 Packet Types 4-5

Neighbor Tables 24-5

Topology Tables 24-6

Route States 24-6

Route Tagging 24-6

Chapter 25 Open Shortest Path First 25-1

Background 25-1

Technology Basics 25-1

Routing Hierarchy 25-2

The SPF Algorithm 25-4

Packet Format 25-4

Additional OSPF Features 25-5

Chapter 26 Exterior Gateway Protocol 26-1

Background 26-1

Technology Basics 26-1

Packet Format 26-2

Message Types 26-3

Neighbor Acquisition 26-3

Neighbor Reachability 26-3 Poll 26-3

Routing Update 26-3

Error 26-4

Chapter 27 border Gateway Protocol 27-1

Background 27-1

Technology Basics 27-1

Packet Format 27-2

Messages 27-2 Open 27-2 Update 27-3

Notification 27-3

Keepalive 27-3

xii Internetworking Technology Overview Chapter 28 OSI Routing 28-1

Background 28-1

Terminology 28-1

ES-IS 28-2

IS-IS 28-3

Routing Hierarchy 28-3

Inter-ES Communication 28-4

Metrics 28-4

Packet Format 28-4

Integrated IS-IS 28-5

Interdomain Routing Protocol IDRP 28-6

PART Bridging Technologies

Chapter 29 Transparent Bridging 29-1

Background 29-1

Technology Basics 29-1

Bridging Loops 29-2

Spanning-Tree Algorithm STA 29-3

Frame Format 29-4

Chapter 30 Source-Route Bridging 30-1

Background 30-1

SRB Algorithm 30-1

Frame Format 30-3

Chapter 31 Mixed-Media Bridging 31-1

Background 31-1

Technology Basics 31-1

Translation Challenges 31-2

Translational Bridging 31-3

Source-Route Transparent Bridging 31-5

Table of Contents xiii PART Network Management

Chapter 32 Simple Network Management Protocol 32-1

Background 32-1

Technology Basics 32-1

Management Model 32-2

Command Types 32-3

Data Representation Differences 32-3

Management Database 32-3

Operations 32-4

Message Format 32-5

Chapter 33 IBM Network Management 33-1

Background 33-1

Functional Areas of Management 33-1 Configuration Management 33-2

Performance and Accounting Management 33-2

Problem Management 33-3

Operations Management 33-3

Change Management 33-3

Principal Management Architectures and Platforms 33-4

The Open Network Architecture Framework 33-4 System View 33-5

NetView 33-5

LAN Network Manager 33-5 SNMP 33-5

Appendix

Appendix References and Recommended Reading A-i

Books and Periodicals A-l

Technical Publications and Standards A-3

Undex

xiv Internetworking Technology Overview Ii OF FGURES

Figure 1-1 Communication Between Two Computer Systems 1-2

Figure 1-2 Relationship Between Adjacent Layers in Single System 1-2

Figure 1-3 Headers and Data 1-3

Figure 2-1 Destination/Next Hop Routing Table 2-2

Figure 2-2 Switching Process 2-3

2-5 Figure 2-3 Slow Convergence and Routing Loops

Figure 3-1 Internetworking Product Functionality 3-2

Figure 3-2 Local and Remote Bridging 3-3

Figure 3-3 IEEE 802.3/IEEE 802.5 Bridging 3-4

Figure 4-1 Typical Network Management Architecture 4-2

Figure 5-1 IEEE 802.3 Physical-Layer Name Components 5-2

Figure 5-2 Ethernet and IEEE 802.3 Frame Formats 5-3

Figure 6-1 IBM Token Ring Network/IEEE 802.5 Comparison 6-2

Figure 6-2 IBM Token Ring Network Physical Connections 6-3

Figure 6-3 IEEE 802 .5/Token Ring Frame Formats 6-4

Figure 7-1 FDDI Standards 7-2

Figure 7-2 FDDI Nodes DAS SAS and Concentrator 7-3

Figure 7-3 FDDI DAS Ports 7-3

Figure 7-4 Station Failure Ring Recovery Configuration 7-4

Figure 7-5 Failed Wiring Ring Recovery Configuration 7-5

Figure 7-6 Use of Optical Bypass Switch 7-6

Figure 7-7 FDDI Frame Format 7-7

Figure 8-1 HSSIs Four Loopback Tests 8-3

Figure 9-1 PPP Frame Format 9-2

Figure 10-1 Sample ISDN Configuration 10-2

Figure 10-2 ISDN Physical-Layer Frame Formats 10-3

Figure 10-3 LAPD Frame Format 10-4

Figure 10-4 ISDN Circuit-Switched Call Stages 10-5

Figure 11-1 SDLC Frame Format 11-2

11-4 Figure 11-2 Typical SDLC-Based Network Configuration

Figure 12-1 X.25 Model 12-2

Figure 12-2 X.25 and the OSI Reference Model 12-2

Figure 12-3 X.25 Frame 12-3

Figure 12-4 X.121 Address Format 12-4

List of Figures xv Figure 12-5 LAPB Frame 12-5

Figure 13-1 Frame Relay Frame 13-3

13-2 Frame Figure Relay Addressing 13-3

Figure 13-3 LMI Message Format 13-4

13-4 Figure Global Addressing Exchange 13-5

Figure 13-5 Hybrid Frame Relay Network 13-6

14-1 Figure SMDS Internetworking Scenario 14-2

Figure 14-2 and Single-CPE Multi-CPE Configurations 14-4

14-3 Figure Encapsulation of User Information by SIP Levels 14-5

Figure 14-4 SIP Level PDU 14-5

Figure 14-5 SIP Level PDU 14-6

15-1 and Figure TDM ATM Multiplexing Techniques 15-2

Figure 15-2 ATM Cell 15-4

15-3 Virtual Figure Connections Through an ATM Switch 15-5

15-4 Figure AAL3/4 Treatment of Payload Frame 15-6

15-5 Figure AAL3/4 SAR Sublayer State Diagram 15-7

15-6 Figure AAL5 Treatment of Payload Frame 15-7

15-7 AAL5 Figure Convergence Sublayer State Diagram 15-8

Figure 15-8 Practical ATM Architecture 15-9

Figure 15-9 ATM PVC Service 15-10

Figure 15-10 ATM SVC Service 15-10

Figure 15-11 ATM Connectionless Service 15-11

16-1 Figure AppleTalk and the OSI Reference Model 16-2

16-2 Figure AppleTalk Address Selection Process 16-3

Figure 16-3 AppleTalk Entities 16-5

16-4 Figure Sample AppleTalk Routing Table 16-6

Figure 16-5 Sample AppleTalk ZIT 16-7

17-1 Figure DNA and the OSI Reference Model 17-2

17-2 Figure DNA Phase IV Routing Layer Header 17-3

Figure 17-3 DECnet Phase IV Routing Protocol Cost Calculation 17-4

Figure 17-4 DECnet Addresses 17-4

17-5 Figure DECnet Level and Level Routers 17-5

Figure 18-1 Internet Protocol Suite and the OSI Reference Model 18-2

Figure 18-2 IP Packet Format 18-3

xvi Internetworking Technology Overview Figure 18-3 Class and Address Formats 18-4

Figure 18-4 Subnet Addresses 18-5

Figure 18-5 Sample Subnet Mask 18-5

Figure 18-6 Internet Architecture 18-6

Figure 18-7 IP Routing Table 18-7

Figure 18-8 TCP Packet Format 18-8

Figure 19-1 NetWare and the OSI Reference Model 19-2

Figure 19-2 IPX Packet Format 19-3

Figure 19-3 Ethernet IEEE 802.3 and IPX Encapsulation Formats 19-4

Figure 20-1 OSI Primitives 20-3

Figure 20-2 OSI Address Format 20-4

Figure 20-3 Principal OSI Upper-Layer Protocols 20-5

Figure 21-1 VINES Protocol Stack 21-1

Figure 21-2 NINES Address Format 21-2

Figure 21-3 VINES Address Selection Process 21-3

Figure 21-4 VINES Routing Algorithm 21-4

Figure 21-5 VIP Packet Format 21-5

Figure 22-1 XNS and the 051 Reference Model 22-2

Figure 22-2 IDP Packet Format 22-3

Figure 23-1 Typical RIP Routing Table 23-1

Figure 23-2 RIP Packet Format 23-2

Figure 23-3 Count-To-Infinity Problem 23-3

Figure 23-4 Split Horizons 23-4

Figure 24-1 Split Horizons 24-2

Figure 25-1 Hierarchical OSPF Internetwork 25-3

Figure 25-2 OSPF Header Format 25-4

Figure 26-1 EGP and the ARPANET 26-1

Figure 26-2 EGP Packet Format 262

Figure 27-1 BGP Packet Format 27-2

Figure 28-1 Hierarchies in OSI Internetworks 28-2

Figure 28-2 ESH and ISH Packet Formats 28-3

Figure 28-3 IS-IS Logical Packet Format 28-4

Figure 28-4 IS-IS Common Header Format 28-5

Figure 29-1 Transparent Bridging Table 29-1

List of Figures xvii Figure 29-2 Inaccurate Forwarding and Learning in Transparent Bridging Environments 29-2

Figure 29-3 Transparent Bridge Network Before Running STA 29-3

Figure 29-4 Transparent Bridge Network After Running STA 29-4

Figure 29-5 Transparent Bridge Configuration Message Format 29-5

Figure 30-1 Sample SRB Network 30-2

Figure 30-2 IEEE 802.5 RIP 30-3

31-1 Figure Bridging Between Transparent Bridging and SRB Domains 31-1

Figure 31-2 Frame Conversion Between IEEE 802.3 and Token Ring 31-4

31-3 Frame Figure Conversion Between Ethernet Type II and Token Ring SNAP 31-4

Figure 31-4 Frame Conversion Between Ethernet Type II 0x80D5 Format and Token Ring 31-5

Figure 32-1 SNMP Management Model 32-2

Figure 32-2 Tree 32-4

Figure 32-3 SNMP Message Format 32-5

Figure 33-1 OSI and IBM Network Management Functions 33-2

Figure 33-2 ONA Framework 33-4

xviii Internetworking Technology Overview OF TABLES

Table 5-1 Ethernet Version and IEEE 802.3 Physical Characteristics 5-2

Table 8-1 HSSI Technical Characteristics 8-2

Table 14-1 Segment Type Values 14-7

Table 15-1 BISDN Service Classes 15-6

Table 18-1 Internet Protocol/Application Mapping 18-9

Table 26-1 EGP Message Types 26-2

ListofTables xix xx Internetworking Technology Overview About This Manual

This section discusses the objectivesaudience organizationand conventions of the Internetworking

Technology Overview publication

Document Objectves

This publication provides technical information on Cisco-supported internetworking technologies It

is designed for use in conjunction with other Cisco manuals or as standalone reference

The Internetworking Technology Overview is not intended to provide all possible information on the

included technologies Because primary goal of this publication is to help network administrators

configure Cisco products the publication emphasizes Cisco-supported technologies however

inclusion of technology in this publication does not necessarily imply Cisco support for that

technology

Audence

The Internetworking Technology Overview is written for anyone who wants to understand

Cisco that readers will information in this internetworking technologies anticipates many use

publication to help configure Cisco products but others also may find it useful

Readers will better understand the material in this publication if they are familiar with networking

terminology Ciscos Internetworking Terms andAcronyms publication is useful reference for those

with minimal knowledge of networking terms

Document Organizaton

This publication is divided into seven parts Each part is concerned with introductory material or

major area of internetworking technology and comprises chapters describing related tasks or functions

Part Internetworking Basics presents concepts basic to the understanding of internetworking

and network management

Part Media-Access Technologies describes standard protocols used for accessing network

physical media

Part Packet-Switching Technologies describes standard protocols used to implement packet-

switching

Part Routed Protocols describes several standard networking protocol stacks that can be

routed through an intemetwork

About This Manual xxi Document Conventions

Part Routing Protocols describes protocols used to route information through an internetwork

Part Bridging Technologies describes protocols and technologies used to provide layer connectivity between subnetworks

Part Network Management describes network management protocols architectures and technologies

Document Conventons

In this publication the following conventions are used

Commands and keywords are in boldface

New important terms are italicized when accompanied by definition or discussion of the term

Protocol names are italicized at their first use in each chapter

Note Means reader take note Notes contain helpful suggestions or references to materials not

contained in this manual

xxii Internetworking Technology Overview

ntroduction to nternetworking

ntroducton

here readers This chapter explains basic intemetworking concepts The information presented helps who are new to internetworking comprehend the technical material that makes up the bulk of this and publication Sections on the OSI reference model important terms and concepts key

organizations are included

OS Reference Mode Mntroduction

Moving information between computers of diverse design is formidable task In the early 1980s

the International Organization for Standardization ISO recognized the need for network model

that would help vendors create interoperable network implementations The Open Systems

Interconnection OSI reference model released in 1984 addresses this need

The OSI reference model quickly became the primary architectural model for intercomputer

communications Although other architectural models mostly proprietary have been created most

network vendors relate their network products to the OSI reference model when they want to educate

users about their products Thus the model is the best tool available to people hoping to learn about network technology

Herarchca Communication

The OSI reference model divides the problem of moving information between computers over

network medium into seven smaller and more manageable problems Each of the seven smaller solved problems was chosen because it was reasonably self-contained and therefore more easily without excessive reliance on external information

devices Each of the seven problem areas is solved by layer of the model Most network implement

all seven layers To streamline operations however some network implementations skip one or more

layers The lower two OSI layers are implemented with hardware and software the upper five layers

are generally implemented in software

The OSI reference model describes how information makes its way from application programs such

in as spreadsheets through network medium such as wires to another application program

another computer As the information to be sent descends through the layers of given system it

looks less and less like human language and more and more like the ones and zeros that computer understands

As an example of OSI-type communication assume that System in Figure 1-1 has information to

send to System The application program in System communicates with System As layer the

top layer which communicates with System As layer which communicates with System As

Introduction to Internetworking 1-1 OSI Reference Model Introduction

layer and so on until System As layer is reached Layer is concerned with putting information

on and taking information oft the physical network medium After the information has traversed

the physical network medium and been absorbed into System it ascends through System Bs

layers in reverse order first layer then layer and so on until it finally reaches System Bs

application program

System System

Network

Figure 1-1 Communication Between Two Computer Systems

Although each of System As layers communicates with its adjacent System layers its primary

is communicate with its in That the of objective to peer layer System is primary objective layer

in System is to communicate with layer in System layer in System communicates with

in This is because each in has certain tasks it layer System and so on necessary layer system

communicate with its in the other must perform To perform these tasks it must peer layer system

The models in different OSI layering precludes direct conmiunication between peer layers systems

Each layer in System must therefore rely on services provided by adjacent System layers to help

achieve between in communication with its System peer The relationship adjacent layers single

system is shown in Figure 1-2

Service user Service user OSI x1 layer layer x1 protocol layer x1 protocol

______I

Service provider OSI layerx layer protocol

Service access points

Figure 1-2 Relationship Between Adjacent Layers in Single System

1-2 Internetworking Technology Overview OSI Reference Model Introduction

Assume layer in System must communicate with layer in System To do this layer in

System must use the services of layer in System Layer is said to be the service user while

layer is the service provider Layer services are provided to layer at service access point

is location which services As the SAP which simply at layer can request layer figure shows

layer can provide its services to multiple layer entities

Unformation Formats

How does layer in System know what layer in System wants Layer 4s specific requests are

in block called header that is stored as control information which is passed between peer layers

prepended to the actual application information For example assume System wishes to send the

following text called data or information to System

The small grey cat ran up the wall to try to catch the red bird

This text is passed from the application program in System to System As top layer System As

application layer must communicate certain information to System Bs application layer so it This prepends that control information in the form of coded header to the actual text to be moved

information unit is passed to System As layer which may prepend its own control information

The information unit grows in size as it descends through the layers until it reaches the network

where the original text and all associated control information travels to System where it is

absorbed by System slayer System slayer strips the layer header reads it and then knows

information unit The smaller infonnation unit is to which how to process the slightly passed layer

strips the layer header analyzes the header for actions layer must take and so forth When the

in it contains the information unit finally reaches the application program System simply original text

of the The concept of header and data is relative depending on the perspective layer currently

analyzing the information unit For example to layer an information unit consists of layer

header and the data that follows Layer 3s data however can potentially contain headers from

layers and Further layer 3s header is simply data to layer This concept is illustrated in

Figure 1-3 Finally not all layers need to append headers Some layers simply perform

readable their transformation on the actual data they receive to make the data more or less to adjacent

layers

System Information units System

Header4 Dataj ______

Header Data

Data

Network CD

Figure 1-3 Headers and Data

Introduction to Internetworking 1-3 OSI Reference Model Introduction

Compatibility Issues

The OSI reference model is not network implementation Instead it specifies the functions of each

layer In this way it is like blueprint for the building of ship After ship blueprint is complete

the ship must still be built Any number of shipbuilding companies can be contracted to do the actual

work just as any number of network vendors can build protocol implementation from protocol

specification And unless the blueprint is extremely impossibly comprehensive ships built by

different shipbuilding companies using the same blueprint will differ from each other in at least

the for it is that the rivets will be in different minor ways At very least example likely places

What accounts for the differences between implementations of the same ship blueprint or protocol

specification In part the differences are due to the inability of any specification to consider every

possible implementation detail Also different implementors will no doubt interpret the blueprint in

slightly different ways And finally the inevitable implementation errors will cause different

implementations to differ in execution This explains why one companys implementation of

protocol does not always interoperate with another companys implementation of that protocol

OSI Layers

Now that the basic features of the OSI layered approach have been described each individual OSI

layer and its functions can be discussed Each layer has predetermined set of functions it must

perform for communication to occur

Application Layer

The application layer is the OSI layer closest to the user It differs from the other layers in that it does services other OSI but rather outside the not provide to any layer to application processes lying of the OSI model of such include scope Examples application processes spreadsheet programs

word-processing programs banking terminal programs and so on

The application layer identifies and establishes the availability of intended communication partners

synchronizes cooperating applications and establishes agreement on procedures for error recovery

and control of data integrity Also the application layer determines whether sufficient resources for the intended communication exist

Presentation Layer

The presentation layer ensures that information sent by the application layer of one system will be

readable by the application layer of another system If necessary the presentation layer translates

between multiple data representation formats by using common data representation format

The presentation layer concerns itself not only with the format and representation of actual user data

but also with data structures used by programs Therefore in addition to actual data format

transformation if necessary the presentation layer negotiates data transfer syntax for the

application layer

Session Layer

terminates sessions between As its name implies the session layer establishes manages and

applications Sessions consist of dialogue between two or more presentation entities recall that the

session layer provides its services to the presentation layer The session layer synchronizes dialogue

between presentation layer entities and manages their data exchange In addition to basic regulation

class of of conversations sessions the session layer offers provisions for data expedition service

and exception reporting of session-layer presentation-layer and application-layer problems

1-4 Internetworking Technology Overview Important Terms and Concepts

Transport Layer

The boundary between the session layer and the transport layer can be thought of as the boundary

between application-layer protocols and lower-layer protocols Whereas the application

presentation and session layers are concerned with application issues the lower four layers are

concerned with data transport issues

The service shields the transport layer attempts to provide data transport that upper layers from

transport implementation details Specifically issues such as how reliable transport over an

is reliable internetwork accomplished are the concern of the transport layer In providing service the

transport layer provides mechanisms for the establishment maintenance and orderly termination of

virtual circuits transport fault detection and recovery and information flow control to prevent one

system from overrunning another with data

Network Layer

The network layer is complex layer that provides connectivity and path selection between two end

systems that may be located on geographically diverse subnetworks subnetwork in this instance

is cable called essentially single network sometimes segment

Because substantial geographic distance and many subnetworks can separate two end systems

desiring communication the network layer is the domain of routing Routing protocols select

optimal paths through the series of interconnected subnetworks Traditional network-layer protocols

then move information along these paths

Link Layer

The link layer formally referred to as the data link layer provides reliable transit of data across

physical link In so doing the link layer is concerned with physical as opposed to network or

will the logical addressing network topology line discipline how end systems use network link

error notification ordered delivery of frames and flow control

Physical Layer

The physical layer defines the electrical mechanical procedural and functional specifications for

activating maintaining and deactivating the physical link between end systems Such maximum characteristics as voltage levels timing of voltage changes physical data rates

transmission distances physical connectors and other similar attributes are defined by physical

layer specifications

mportant Terms and Concepts

Internetworking like other sciences has terminology and knowledge base all its own

Unfortunately because the science of internetworking is so young universal agreement on the

meaning of networking concepts and terms has not yet occurred Definitions of internetworking

terms will become more rigidly defined and used as the internetworking industry matures

Addressing

Locating computer systems on an internetwork is an essential component of any network system

There are various addressing schemes used for this purpose depending on the protocol family being

used In other words AppleTalk addressing is different from TCP/IP addressing which in turn is

different from OSI addressing and so on

Introduction to Internetworking 1-5 Key Organizations

and addresses Two important types of addresses are link-layer addresses network-layer Link-layer

for each network addresses also called physical or hardware addresses are typically unique connection In fact for most local-area networks LANs link-layer addresses are resident in the

defined the standard interface circuitry and are assigned by the organization that protocol network represented by the interface Because most computer systems have one physical

and other connected to connection they have only single link-layer address Routers systems

their multiple physical networks can have multiple link-layer addresses As name implies link-layer

addresses exist at layer of the OSI reference model

of the OSI Network-layer addresses also called virtual or logical addresses exist at layer address reference model Unlike link-layer addresses which usually exist within fiat space mail which network-layer addresses are usually hierarchical In other words they are like addresses address describe persons location by providing country state zip code city street an on

the street and finally name One good example of flat address space is the U.S social security

social number numbering system where each person has single unique security

Hierarchical addresses make address sorting and recall easier by eliminating large blocks of

logically similar addresses through series of comparison operations For example we can

eliminate all other countries if an address specifies the country Ireland Easy sorting and recall is one

reason that routers use network-layer addresses as the basis for routing

but use Network-layer addresses differ depending on the protocol family being used they typically Some of these similar logical divisions to find computer systems on an internetwork logical

network is divisions are based on physical network characteristics such as the segment system

basis the located on others are based on groupings that have no physical for example AppleTalk zone

Frames Packets and Messages

Once addresses have located computer systems information can be exchanged between two or more

units of of these systems Networking literature is inconsistent in naming the logically grouped information that move between computer systems The termsframepacket protocol data unit of those write PDU segment message and others have all been used based on the whim who

protocol specifications

and destination is In this publication the term frame denotes an information unit whose source

and destination is link-layer entity The term packet denotes an information unit whose source

unit whose and network-layer entity Finally the term message denotes an information source

used refer lower- destination entity exists above the network layer Message is also to to particular

layer information units with specific well-defined purpose

Key Organzatons would be Without the services of several key standards organizations the world of networking

substantially more chaotic than it is currently Standards organizations provide forums for

discussion help turn discussion into formal specifications and proliferate the specifications once

they complete the standardization process

formal standards Most standards organizations have specific processes for turning ideas into

similar in that Although these processes differ slightly between standards organizations they are

draft they all iterate through several rounds of organizing ideas discussing the ideas developing

the standards voting on all or certain aspects of the standards and finally formally releasing

completed standard to the public

1-6 Internetworking Technology Overview Key Organizations

Some of the better-known standards organizations are

International Organization for Standardization ISOAn international standards organization

responsible for wide range of standards including those relevant to networking This

organization is responsible for the OSI reference model and the OSI protocol suite

American National Standards Institute ANSIThe coordinating body for voluntary standards

within the United States ANSI is member of ANSIs best-known groups ISO communications

standard is FDDI

Electronic Industries Association EIAA group that specifies electrical transmission

standards EIAs best-known standard is RS-232

Institute of Electrical and Electronic Engineers IEEE professional organization that defines

network standards IEEE LAN standards including IEEE 802.3 and IEEE 802.5 are the best-

known IEEE communications standards and are the predominant LAN standards in the world today

Consultative Committee for International Telegraph and Telephone CCITT An international

organization that develops communication standards CCITTs best-known standard is X25

Internet Activities Board lAB group of internetwork researchers who meet regularly to

discuss issues pertinent to the Internet This board sets much of the policy for the Internet through

decisions and assignment of task forces to various issues Some Request for Comments RFC

documents are designated by the lAB as Internet standards including Transmission Control

Protocol/Internet Protocol TCP/IP and the Simple Network Management Protocol SNMP

Introduction to Internetworking 1-7 Key Organizations

1-8 Internetworking Technology Overview Routing Basics

Background

internetwork from to destination the at Routing is moving information across an source Along way which least one intermediate node is typically encountered Routing is often contrasted with bridging

difference between the two is that seems to accomplish precisely the same thing The primary

the reference while occurs at bridging occurs at layer the link layer of OSI model routing layer

the network layer This distinction provides routing and bridging with different information to

in of information from source to destination.As result routing and bridging use the process moving several different kinds of and accomplish their tasks in different ways and in fact there are routing Basics bridging For more information on bridging see Chapter Bridging

literature for two but The topic of routing has been covered in computer science over decades

The for this time routing only achieved commercial popularity in the mid-1980s primary reason lag

is the nature of networks in the l970s During this time networks were fairly simple homogeneous

has environments Only recently large-scale internetworking become popular

Routng Components

determination of and the of Routing involves two basic activities optimal routing paths transport

internetwork In this the latter information groups typically called packets through an publication

of these is referred to as switching Switching is relatively straightforward Path determination on

the other hand can be very complex

Path Determnaton

is used metric is standard of measurementfor example path lengththat by routing

aid the of determination algorithms to determine the optimal path to destination To process path which contain route information Route routing algorithms initialize and maintain routing tables

information varies depending on the routing algorithm used

Destination/next Routing algorithms fill routing tables with variety of information hop

the associations tell router that particular destination can be gained optimally by sending packet

the final destination When router to particular router representing the next hop on the way to and to associate this address receives an incoming packet it checks the destination address attempts table with next hop Figure 2-1 shows an example of destination/next hop routing

Routing Basics 2-1 Routing Components

To reach network Send to

27 Node

57 Node

17 Node

24 Node

52 Node

16 Node

26 Node

Figure 2-1 Destination/Next Hop Routing Table

tables also contain other Routing can information such as information about the desirability of Routers metrics determine path compare to optimal routes Metrics differ depending on the design

of the routing algorithm being used variety of common metrics will be introduced and described

later in this chapter

Routers communicate with one another and maintain their routing tables through the transmission of of The variety messages routing update message is one such message Routing updates

consist of all generally or portion of routing table By analyzing routing updates from all routers router build detailed can picture of network topology link-state advertisement is another of example message sent between routers Link-state advertisements inform other routers of the

state of the senders links Link information can also be used to build complete picture of network Once the topology network topology is understood routers can determine optimal routes to network destinations

Switch ug

Switching algorithms are relatively simple and are basically the same for most routing protocols In host most cases determines that it must send packet to another host Having acquired routers address by some means the source host sends packet addressed specifically to routers physical Access Media Control MAC-layeraddress but with the protocol network-layer address of the destination host

On the examining packets destination protocol address the router determines that it either knows does know how or not to forward the packet to the next hop If the router does not know how to

forward the it packet typically drops the packet If the router knows how to forward the packet it the destination changes physical address to that of the next hop and transmits the packet

The next or not be the ultimate destination If the hop may may host not next hop is usually another which the router executes same switching decision process As the packet moves through the

its address but its address remains internetwork physical changes protocol constant This process is illustrated in Figure 2-2

2-2 Internetworkirig Technology Overview Routing Algorithms

Source host Packet PC

To Destination host Protocol address Router Physical addJ

Packet

To Destination host Protocol address Router Physical address

Packet

Destination host Protocol address Destination host Physical address

Destination host Packet PC

Figure 2-2 Switching Process

and destination end The The preceding discussion describes switching between source system

hierarchical that International Organization for Standardization ISO has developed terminology

network devices without the to is useful in describing this process Using this terminology ability while network devices with forward packets between subnetworks are called end systems ESs

further divided into those that these capabilities are referred to as intermediate systems ISs ISs are

that communicate both within can communicate within routing domains intradomain ISs and those

is considered to be and between routing domains interdomain ISs routing domain generally

set of portion of an internetwork under common administrative authority regulated by particular

With certain administrative guidelines Routing domains are also called autonomous systems but intradomain protocols routing domains may also be divided into routing areas routing

protocols are still used for switching both within and between areas

Routng AHgorthms

characteristics the Routing algorithms can be differentiated based on several key First particular Second there goals of the algorithm designer affect the operation of the resulting routing protocol

different network and router are various types of routing algorithms Each algorithm has impact on

metrics that affect calculation of resources Finally routing algorithms use variety of optimal attributes routes The following sections analyze these routing algorithm

Routing Basics 2-3 Routing Algorithms

Desgn Goals

Routing algorithms often have one or more of the following design goals

Optimality

Simplicity and low overhead

Robustness and stability

Rapid convergence

Flexibility

Optimality

Optimality refers to the ability of the routing algorithm to select the best route The best route

depends on the metrics and metric weightings used to make the calculation For example one

routing algorithm might use number of hops and delay but might weight delay more heavily in the calculation Naturally routing protocols must strictly define their metric calculation algorithms

Simplicity

Routing algorithms are also designed to be as simple as possible In other words the routing

algorithm must offer its functionality efficiently with minimum of software and utilization

overhead Efficiency is particularly important when the software implementing the routing

algorithm must run on computer with limited physical resources

Robustness

Routing algorithms must be robust In other words they should perform correctly in the face of

unusual or unforeseen circumstances such as hardware failures high load conditions and incorrect

implementations Because routers are located at network junction points they can cause

considerable problems when they fail The best routing algorithms are often those that have

withstood the test of time and proven stable under variety of network conditions

Rapid Convergence

Routing algorithms must converge rapidly Convergence is the process of agreement by all routers on When network optimal routes event causes routes to either go down or become available

routers distribute routing update messages Routing update messages penneate networks recalculation of stimulating optimal routes and eventually causing all routers to agree on these

routes that Routing algorithms converge slowly can cause routing loops or network outages

Figure 2-3 shows routing ioop In this case packet arrives at Router at time ti Router has

already been updated and so knows that the optimal route to the destination calls for Router to be the Router therefore next stop forwards the packet to Router Router has not yet been updated

and believes that the so optimal next hop is Router Router therefore forwards the packet back

to Router The packet will continue to bounce back and forth between the two routers until

Router receives its routing update or until the packet has been switched the maximum number of times allowed

2-4 Internetworking Technology Overview Routing Algorithms

rXPacket to

table Routing table Routing

Send to Dest Sendto flDt

Already updated Not yet updated

Figure 2-3 Slow Convergence and Routing Loops

Flexibility

should and Routing algorithms should also be flexible In other words routing algorithms quickly

network circumstances For assume that network accurately adapt to variety of example segment select has gone down Many routing algorithms on becoming aware of this problem will quickly

that can be the next-best path for all routes normally using segment Routing algorithms network router network and other programmed to adapt to changes in bandwidth queue size delay variables

Types be Routing algorithms can be classified by type For example algorithms can

Static or dynamic

Single-path or multipath

Flat or hierarchical

Host-intelligent or router-intelligent

Intradomain or interdomain

Link state or distance vector

Static or Dynamic

all Static table are established Static routing algorithms are hardly algorithms at routing mappings unless the by the network administrator prior to the beginning of routing They do not change and work network administrator changes them Algorithms that use static routes are simple to design

is well in environments where network traffic is relatively predictable and network design relatively

simple

network are considered Because static routing systems cannot react to changes they generally

unsuitable for todays large constantly changing networks Most of the dominant routing algorithms

in the 1990s are dynamic

network circumstances do this Dynamic routing algorithms adjust in real time to changing They

indicates that network has by analyzing incoming routIng update messages If the message change sends These occurred the routing software recalculates routes and out new routing update messages

their and their messages permeate the network stimulating routers to rerun algorithms change

routing tables accordingly

Routing Basics 2-5 Routing Algorithms

be Dynamic routing algorithms may supplemented with static routes where appropriate For

router last example of resort router to which all unroutable packets are sent may be designated

This router acts as repository for all unroutable packets ensuring that all messages are at least handled in some way

SinglePath or Multipath Some sophisticated routing protocols support multiple paths to the same destination These

multipath algorithms permit traffic multiplexing over multiple lines single-path algorithms do not The of advantages multipath algorithms are obvious they can provide substantially better

throughput and reliability

Flat or Hierarchical

Some routing algorithms operate in flat space while others use routing hierarchies In flat routing

system all routers are peers of all others In hierarchical routing system some routers form what

amounts to routing backbone Packets from nonbackbone routers travel to the backbone routers

where they are sent through the backbone until they reach the general area of the destination At this

point they travel from the last backbone router through one or more nonbackbone routers to the final destination

often Routing systems designate logical groups of nodes called domains autonomous systems or

areas In hierarchical systems some routers in domain can communicate with routers in other while others domains can only communicate with routers within their domain In very large networks additional hierarchical levels may exist Routers at the highest hierarchical level form the routing backbone

The primary advantage of hierarchical routing is that it mimics the organization of most companies

and therefore their supports traffic patterns very well Most network communication occurs within small company groups domains Intradomain routers only need to know about other routers within

their their domain so routing algorithms can be simplified Depending on the routing algorithm

being used routing update traffic can be reduced accordingly

Host-lDtelligent or RouterluteUIigent

Some routing algorithms assume that the source end-node will determine the entire route This is referred usually to as source routing In source-routing systems routers merely act as store-and- forward devices mindlessly sending the packet to the next stop

Other algorithms assume that hosts know nothing about routes In these algorithms routers

determine the the internetwork based their calculations path through on own In the first system the hosts have the routing intelligence In the latter system routers have the routing intelligence

The trade-off between host-intelligent and router-intelligent routing is one of path optimality versus

traffic overhead Host-intelligent systems choose the better routes more often because they typically

discover all the possible routes to destination before the packet is actually sent They then choose

the best based that path on particular systems definition of optimal The act of determining all often routes however requires substantial discovery traffic and significant amount of time

Iritradomain or luterdomain

Some routing algorithms work only within domains others work within and between domains The nature of these two algorithm types is different It stands to reason therefore that an optimal intradomain routing algorithm would not necessarily be an optimal interdomain routing algorithm

2-6 Internetworking Technology Overview Routing Algorithms

Link State or Distance Vector

flood information to all Link state algorithms also known as shortest path first algorithms routing

of the table that nodes in the internetwork However each router sends only that portion routing

describes the state of its own links Distance vector algorithms also known as Bellman-Ford

but to its algorithms call for each router to send all or some portion of its routing table only while distance vector neighbors In essence link state algorithms send small updates everywheie routers algorithms send larger updates only to neighboring

link are somewhat less to routing loops Because they converge more quickly state algorithms prone

than distance vector algorithms On the other hand link state algorithms require more Cpu power

and memory than distance vector algorithms Link state algorithms can therefore be more expensive both well in most to implement and support Despite their differences algorithm types perform

circumstances

Metrics

select the best route But Routing tables contain information used by switching software to how

tables built What is the nature of the information they contain specifically are routing specific others How do routing algorithms determine that one route is preferable to

the best route Routing algorithms have used many different metrics to determine Sophisticated

selection metrics them in single hybrid routing algorithms can base route on multiple combining

metric All of the following metrics have been used

Path length

Reliability

Delay

Bandwidth

Load

Communication cost

Path Length

allow network Path length is the most common routing metric Some routing protocols

link In this is the sum of administrators to assign arbitrary costs to each network case path length define metric that the costs associated with each link traversed Other routing protocols hop count

as routers that packet must specifies the number of passes through internetworking products such

take en route from source to destination

Reliability

refers to the usually described in terms Reliability in the context of routing algorithms reliability down more often than others of the bit-error rate of each network link Some network links may go than other links Once down some network links may be repaired more easily or more quickly Any

in the of reliability ratings Reliability ratings reliability factors can be taken into account assignment

links network administrators are typically arbitrary are usually assigned to network by They numeric values

Routing Basics 2-1 Routed vs Routing Protocols

Delay

Routing delay refers to the length of time required to move packet from source to destination

through the internetwork Delay depends on many factors including the bandwidth of intermediate network the each links port queues at router along the way network congestion on all intermediate

network links and the physical distance to be travelled Because it is conglomeration of several

important variables delay is common and useful metric

Bandwidth

Bandwidth refers the to available traffic capacity of link All other things being equal lOMbps Ethernet link would be preferable to 64-kbps leased line Although bandwidth is rating of the maximum attainable throughput on link routes through links with greater bandwidth do not

better necessarily provide routes than routes through slower links If for example faster link is much the actual busier time required to send packet to the destination may be greater through the fast link

Load

Load refers to the to which network degree resource such as router is busy Load may be

calculated in of utilization variety ways including CPU and packets processed per second Monitoring these parameters on continual basis can itself be resource intensive

Communication Cost

Communication cost is another metric important Some companies may not care about performance as much as care about they operating expenditures Even though line delay might be longer they will

send packets over their own lines rather than lines that will through public cost money for usage time

Routed vs Routng Protocos

Confusion about the terms routed protocol and routing protocol is common Routed protocols are

that routed protocols are over an internetwork Examples of such protocols are the Internet Protocol DECnet IP AppleTalk NetWare OSI Banyan VINES and Xerox Nttwork System XNS Routing that protocols are protocols implement routing algorithms Put simply they route routed protocols an internetwork through Examples of these protocols include Interior Gateway Routing Protocol IGRPEnhanced Interior Gateway Routing Protocol EIGRP Open Shortest Path First OSPF Exterior Gateway Protocol EGPBorder Gateway Protocol BGP OSI RoutingAdvanced Peer to-Peer Intermediate Networking System to Intermediate System IS-IS and Routing Information Protocol Routed and RIP routing protocols are discussed in detail later in this publication

2-8 Internetworking Technology Overview CHAPTER

Bridging Basics

Background

Bridges became commercially available in the early 1980s At the time of their introduction bridges

connected and enabled packet forwarding between homogeneous networks More recently bridging

between different networks has also been defined and standardized

Several kinds of bridging have emerged as important Transparent bridging is found primarily in

Ethernet environments Source-route bridging is found primarily in Token Ring environments

Translational bridging provides translation between the formats and transit principles of different combines the media types usually Ethernet and Token Ring Source-route transparent bridging

algorithms of transparent bridging and source-route bridging to allow communication in mixed

EthernetlToken Ring environments

in routers has taken The diminishing price and the recent inclusion of bridging capability many

that have survived include features substantial market share away from pure bridges Those bridges and such as sophisticated filteringpseudo-intelligent path selection high throughput rates Although

an intense debate about the benefits of bridging versus routing raged in the late 1980s most people

now agree that each has its place and that both are often necessary in any comprehensive

internetworking scheme

nternetworking Device Comparison

network There Internetworking devices offer communication between local area LAN segments and These are four primary types of internetworking devices repeaters bridges routers gateways which devices can be differentiated very generally by the Open System Interconnection OS layer at

they establish the LAN-to-LAN connection Repeaters connect LANs at OSI layer bridges connect

LANs at layer routers connect LANs at layer and gateways connect LANs at layers through and the Each device offers the functionality found at its layers of connection uses functionality

of all lower layers This idea is portrayed graphically in Figure 3-1

Bridging Basics 3-1 Technology Basics

End node __ I__End node End__ node End node ______I______I______Bridge ______Repeater ______I______

End node End node End node Gateway End node ___ I___ I___ I______Router ______ri I__I______

3-1 Figure Internetworking Product Functionality

TechnoHogy Bascs

Bridging occurs at the link which controls data layer flow handles transmission errors provides

physical as to and opposed logical addressing manages access to the physical medium Bridges provide these functions various by using link-layer protocols that dictate specific flow control error handling and media-access addressing algorithms Examples of popular link-layer protocols include Ethernet Token Ring and FDDI

Bridges are not devices complicated They analyze incoming frames make forwarding decisions based information on contained in the frames and forward the frames toward the destination In

some cases for example source-route bridging the entire path to the destination is contained in each frame In other cases for example transparent bridging frames are forwarded one hop at time toward the destination See Chapter 30 Source-Route Bridging and Chapter 29 Transparent Bridging respectively for more information source-route on bridging and transparent bridging

Upper-layer protocol transparency is of Because primary advantage bridging bridges operate at the link are not to examine layer they required upper-layer information This means that they can

forward traffic rapidly representing any network-layer protocol It is not uncommon for bridge to

move AppleTalk DECnet TCP/IP XNS and other traffic between two or more networks

are of frames based Bridges capable filtering on any layer fields For example bridge can be

to all programmed reject not forward frames sourced from particular network Since link-layer information often includes reference to an upper-layer protocol bridges can usually filter on this

filters can be parameter Further helpful in dealing with unnecessary broadcast and multicast packets

3-2 Internetworking Technology Overview Types of Bridges

several By dividing large networks into self-contained units bridges provide advantages First

diminishes the traffic because only some percentage of traffic is forwarded the bridge experienced

by devices on all connected segments Second the bridge acts as firewall for some potentially between number of damaging network errors Third bridges allow for communication larger extend devices than would be supported on any single LAN connected to the bridge Fourth bridges

stations that not the effective length of LAN permitting attachment of distant were previously connected

Types of Brdges

characteristics Bridges can be grouped into categories based on various product Using one popular

direct connection classification scheme bridges are either local or remote Local bridges provide

between multiple LAN segments in the same area Remote bridges connect multiple LAN segments

shown in in different areas usually over telecommunications lines These two configurations are

Figure 3-2

Ethernet

bridging

Figure 3-2 Local and Remote Bridging

One of these is the difference Remote bridging presents several unique internetworking challenges between LAN and wide area network WAN speeds Although several fast WAN technologies are

are often an now establishing presence in geographically dispersed internetworks LAN speeds

order of magnitude faster than WAN speeds Vastly different LAN and WAN speeds sometimes from over the WAN prevent users running delay-sensitive LAN applications

for Remote bridges cannot improve WAN speeds but can compensate speed discrepancies through

transmission rate wishes to sufficient buffering capability If LAN device capable of 3-Mbps

communicate with device on remote LAN the local bridge must regulate the 3-Mbps data stream

the data in so that it does not overwhelm the 64-kbps serial link This is done by storing incoming

serial link accommodate This on-board buffers and sending it over the serial link at rate the can the can be achieved only for short bursts of data that do not overwhelm bridges buffering capability

divided the OSI link into two The Institute of Electrical and Electronic Engineers IEEE has layer Media Control and the link control separate sublayers the Access MAC sublayer logical LLC token sublayer The MAC sublayer permits and orchestrates media access for example contention flow passing or others while the LLC sublayer is concerned with framing control error control

and MAC-sublayer addressing

networks Some bridges are MAC-layer bridges These devices bridge between homogeneous for

different example IEEE 802.3 and IEEE 802.3 Other bridges can translate between link-layer The basic mechanics of such translation are protocols for exampleIEEE 802.3 and IEEE 802.5

shown in Figure 3-3

Bridging Basics 3-3 Types of Oridges

Host Host

Bridge

LLC PKT

Link MAC 802.3 PKTW8O2.5 PKT

Physical

Figure 3-3 IEEE 802.3/IEEE 002.5 BrIdging

In the figure the IEEE 802.3 host Host formulates packet containing application information

and encapsulates the packet in an IEEE 802.3compatible frame for transit over the IEEE 802.3

medium to the bridge At the bridge the frame is stripped of its IEEE 802.3 header at the MAC of the link sublayer layer and is subsequently passed up to the LLC sublayer for further processing

After this processing the packet is passed back down to an IEEE 802.5 implementation which

encapsulates the packet in an IEEE 8025 header for transmission on the IEEE 802.5 network to the IEEE 802.5 host Host

bridges translation between networks of different types is never perfect because it is likely that

network will one support certain frame fields and protocol functions not supported by the other network Many bridging translation issues are discussed in more detail in Chapter 31 Mixed-Media Bridging

3-4 Internetworkirig Technology Overview iSc TE

Network Management Basics

Background

in the of network As companies The early 1980s saw tremendous expansion area deployment

realized the cost benefits and productivity gains created by network technology they began adding network technologies and networks and expanding existing networks almost as rapidly as new

the from this expansion were being felt products were introduced By mid-1980s growing pains

that had different and incompatible network especially by those companies deployed many

technologies

associated with network are network operation The primary problems expansion day-to-day network each new network technology management and strategic growth planning Specifically

and maintain In the 1980s strategic planning for the requires its own set of experts to operate early alone for large growth of these networks became nightmare The staffing requirements managing

created crisis for Automated network management heterogeneous networks many organizations network across diverse including what is typically called capacity planning integrated

environments became an urgent need

to most network architectures and This chapter describes technical features common management

functional of as defined by the International protocols It also presents the five areas management

Organization for Standardization ISO

Network Management Architecture

and set of End Most network management architectures use the same basic structure relationships and other network devices run software stations managed devices such as computer systems

Problems are recognized when one or allowing them to send alerts when they recognize problems these entities are more user-determined thresholds are exceeded Upon receiving alerts management

all of of actions including programmed to react by executing one several or group

Operator notification

Event logging

System shutdown

Automatic attempts at system repair

stations check the values of certain variables Polling can Management entities can also poll end to these are be automatic or user initiated Agents in the managed devices respond to polls Agents

about the devices in which they reside store software modules that compile information managed

and it or reactively to management this information in management database provide proactively via network Well-known entities within network management systems management protocol Network Protocol and network management protocols include the Simple Management SNMP

Network Management Basics 4-1 The ISO Network Management Model

Common Management Information Protocol CMIP Management proxies are entities that provide

management information on behalf of other entities typical network management architecture is

shown in Figure 4-1

Network management system

4qKtty

Network management

protocol

Managed devices

Figure 4-1 Typical Network Management Architecture

The SO Network Management ModeD

The ISO has contributed great deal to network standardization .Their network management model

is the for primary means understanding the major functions of network management systems This model consists of five conceptual areas

Performance management

Configuration management

Accounting management

Fault management

Security management

Performance Management

The of is to and make available goal performance management measure various aspects of network

performance so that internetwork performance can be maintained at an acceptable level Examples

of variables that be include network performance might provided throughput user response times

and line utilization

4-2 lnternetworking Technology Overview The ISO Network Manaqement Model

Performance management involves several steps

Gather performance data on those variables of interest to network administrators

Analyze the data to determine normal baseline levels

thresholds for each variable such that exceeding Determine appropriate performance important of these thresholds indicates network problem worthy of attention

When threshold is Management entities continually monitor performance variables performance

exceeded an alert is generated and sent to the network management system

of the to reactive When performance Each of the steps just described is part process setup system exceeded user-defined the reacts by sending becomes unacceptable by virtue of an threshold system methods For network message Performance management also permits proactive example will affect metrics Such simulation can be used to project how network growth performance

so that counteractive simulation can effectively alert administrators to impending problems

measures can be taken

ConfiglJraton Management

network and information The goal of configuration management is to monitor system configuration versions of hardware and software elements can so that the effects on network operation of various elements have be tracked and managed Because all hardware and software operational quirks

information is to flaws or both that might affect network operation such important maintaining

smooth-running network

associated with it For an Each network device has variety of version information example follows engineering workstation might be configured as

Operating system version 3.2

Ethernet interface version 5.4

TCP/IP software version 2.0

NetWare software version 4.1

NFS software version 5.1

Serial communications controller version 1.1

X.25 software version 1.0

SNMP software version 3.1

information in database for access When Configuration management subsystems store this easy

clues that solve the problem occurs this database can be searched for might help problem

Accountng Management

that individual is to measure network utilization so The goal of accounting management parameters network be Such regulation minimizes network or group uses of the can regulated appropriately be out based on resource capacities and problems because network resources can apportioned

maximizes the fairness of network access across all users

is to the first toward accounting management As with performance management step appropriate of the results insight into measure utilization of all important network resources Analysis provides

be set at this Some correction will be required to current usage patterns Usage quotas can point

Network Management Basics 4-3 The ISO Network Management Model

reach optimal access practices From that point on ongoing measurement of resource use can yield

billing information as well as information used to assess continued fair and optimal resource utilization

Fault Management

The goal of fault management is to detect log notify users of and to the extent possible

automatically fix network problems in order to keep the network running effectively Because faults downtime can cause or unacceptable network degradation fault management is perhaps the most widely implemented of the ISO network management elements

Fault management involves several steps

Determine problem symptoms

Isolate the problem

Fix the problem

Test the fix on all important subsystems

Record the problems detection and resolution

Security Management

The goal of security management is to control access to network resources according to local

guidelines so that the network cannot be sabotaged intentionally or unintentionally and sensitive

information cannot be accessed by those without appropriate authorization For example security

management subsystem can monitor users logging onto network resource refusing access to those

who enter inappropriate access codes

Security management subsystems work by partitioning network resburces into authorized and unauthorized For areas some users access to any network resources is inappropriate Such users are usually company outsiders For other internal network users access to information originating

from particular department is inappropriate For example access to human resource files is

inappropriate for most users outside the human resource department

Security management subsystems perform several functions

Identify sensitive network resources including systems files and other entities

Determine mappings between sensitive network resources and user sets

Monitor access points to sensitive network resources

Log inappropriate access to sensitive network resources

4-4 Internetworking Technology Overview

Ethernet/i EEE 8023

Background

in the 1970s Ethernet was developed by Xerox Corporations Palo Alto Research Center PARC released Ethernet was the technological basis for the IEEE 802.3 specification which was initially and in 1980 Shortly thereafter Digital Equipment Corporation Intel Corporation Xerox

and released Ethernet that is Corporation jointly developed an specification Version 2.0 Ethernet and IEEE 8023 maintain the substantially compatible with IEEE 802.3 Together currently

share of local-area network the term Ethernet is often greatest market any LAN protocol Today that used to refer to all carrier sense multiple access/collision detection CSMA/CD LANs 802.3 generally conform to Ethernet specifications including IEfiE

middle between low- When it was developed Ethernet was designed to fill the ground long-distance

networks data at for speed networks and specialized computer-room carrying high speeds very

limited distances Ethernet is well suited to applications where local communication medium must

traffic at data rates carry sporadic occasionally heavy high peak

EthernetflEEE 802.3 Comparson

Stations on Ethernet and IEEE 802.3 specify similar technologies Both are CSMA/CD LANs

CSMA/CD LAN can access the network at any time Before sending data CSMA/CD stations

transmit waits If listen to the network to see if it is already in use If it is the station wishing to

stations listen for the network is not in use the station transmits collision occurs when two

and transmit In this both transmissions are network traffic hear none simultaneously case determine when the damaged and the stations must retransmit at some later time Backoff algorithms know when must colliding stations retransmit CSMA/CD stations can detect collisions so they they

retransmit

Both Ethernet and IEEE 802.3 LANs are broadcast networks In other words all stations see all

station must examine frames regardless of whether they represent an intended destination Each

station is destination If the frame is to received frames to determine if the so passed higher

protocol layer for appropriate processing

Differences between Ethernet and IEEE 802.3 LANs are subtle Ethernet provides services

while IEEE 802.3 the corresponding to layers and of the OSI reference model specifies physical

the link but does not define logical layer layer and the channel-access portion of layer layer

in hardware the link control protocol Both Ethernet and IEEE 802.3 are implemented Typically

interface card in host or on physical manifestation of these protocols is either an computer circuitry

primary circuit board within host computer

Ethernet/IEEE 802.3 5-1 Physical Connections

Physical CoDnections

IEEE 802.3 specifies several different physical layers whereas Ethernet defines only one Each

IEEE 802.3 physical layer protocol has name that summarizes its characteristics The coded

components of an IEEE 802.3 physical-layer name are shown in Figure 5-1

Figure 5-1 IEEE 802.3 Physical-Layer Name Components

of summary Ethernet Version and IEEE 802.3 characteristics appears in Table 5-1

Table 5-1 Ethernet Version and IEEE 802.3 Physical Characteristics

Ethernet IEEE 802.3 Values Characteristic Value lOBaseS lOBase2 lUaseS lOBaseT lOBroad36

Data rate 10 10 10 10 10 Mbps

Signaling Baseband Baseband Baseband Baseband Baseband Broadband method

Maximum segment 500 500 185 250 100 1800

length Unshielded

twisted pair

Media 50-ohm 50-ohm 50-ohm Unshielded Unshielded 75-ohm

coax thick coax thick coax thin twisted pair twisted pair coax

Topology Bus Bus Bus Star Star Bus

Ethernet is most similar to IEEE 8023 lOBaseS Both of these protocols specify bus topology

network with connecting cable between the end stations and the actual network medium In the

case of Ethernet that cable is called transceiver cable The transceiver cable connects to

transceiver device attached to the physical network medium The IEEE 8023 configuration is much

the that the cable is referred attachment unit and same except connecting to as an interface AUI the transceiver is called medium attachment unit MAU In both cases the connecting cable

attaches to an interface board or interface circuitry within the end station

5-2 Internetworking Technology Overview Frame Formats

Frame Formats

Ethernet and IEEE 802.3 frame formats are shown in Figure 5-2

Ethernet

Field length

in bytes 46-1500

IEEE 802.3

Field length

in bytes 46-1 500

Destination Source 802.2 header Preamble Length FCS address address and data

SOF Start-of-frame delimiter FCS Frame check sequence

Figure 5-2 Ethernet and IEEE 802.3 Frame Formats

Both Ethernet and IEEE 802.3 frames begin with an alternating pattern of ones and zeros called

preamble The preamble tells receiving stations that frame is coming

802.3 frame is The byte before the destination address in both an Ethernet and IEEE start-of-

frame delimiter This byte ends with two consecutive one bits which serve to synchronize the frame

reception portions of all stations on the LAN

the destination and Immediately following the preamble in both Ethernet and IEEE 802.3 LANs are

source address fields Both Ethernet and IEEE 802.3 addresses are six bytes long Addresses are

contained in hardware on the Ethernet and IEEE 802.3 interface cards The first three bytes of the

last three addresses are specified by the IEEE on vendor-dependent basis while the bytes are unicast specified by the Ethernet or IEEE 802.3 vendor The source address is always single node address while the destination address may be unicast multicast group or broadcast all nodes

This field In Ethernet frames the 2-byte field following the source address is type field specifies

the upper-layer protocol to receive the data after Ethernet processing is complete

which indicates In IEEE 802.3 frames the 2-byte field following the source address is length field

field the number of bytes of data that follow this field and precede the frame check sequence FCS

and Following the type/length field is the actual data contained in the frame After physical-layer

In the link-layer processing is complete this data will eventually be sent to an upper-layer protocol IEEE case of Ethernet the upper-layer protocol is identified in the type field In the case of 802.3

If data in the the upper-layer protocol must be defined within the data portion of the frame if at all

inserted frame is insufficient to fill the frame to its minimum 64-byte size padding bytes are to

ensure at least 64-byte frame

value The After the data field is four-byte FCS field containing cyclic redundancy check CRC

CRC is created by the sending device and recalculated by the receiving device to check for damage

that might have occurred to the frame in transit

Ethernet/iEEE 802.3 5-3 Frame Formats

5-4 Internetworking Technology Overview Token Ring/H EEE 8O25

Background

The Token Ring network was originally developed by IBM in the 970s It is still IBMs primary

local-area network LAN technology and is second only to Ethernet/IEEE 802.3 in general LAN

popularity The IEEE 802.5 specification is almost identical to and completely compatible with

IBMs Token Ring network In fact the IEEE 802.5 specification was modeled after IBM Token

Ring and continues to shadow IBMs Token Ring development The term Token Ring is generally

used to refer to both IBMs Token Ring network and IEEE 802.5 networks

Token Ring/il EEE 8O25 Comparison

Token Ring and IEEE 802.5 networks are basically quite compatible although the specifications

with all end stations differ in relatively minor ways IBMs Token Ring network specifies star attached to device called multistation access unit MSAU whereas IEEE 802.5 does not specify Other topology although virtually all IEEE 802.5 implementations also are based on star while differences exist including media type IEEE 802.5 does not specify media type IBM Token

Ring networks use twisted pair and routing information field size Figure 6-1 summarizes IBM

Token Ring network and IEEE 802.5 specifications

Token Ring/IEEE 802.5 6-1 Token Passing

IBM Token Ring network IEEE 802.5

Data rates 4.16 Mbps 4.16 Mbps

260 shielded

twisted pair Stations/segment 250 72 unshielded

twisted_pair

Topology Star Not specified

Media Twisted pair Not specified

Signaling Baseband Baseband

Access method Token passing Token passing

Differential Differential Encoding Manchester Manchester

Figure 6-1 IBM Token Ring Network/IEEE 802.5 Comparison

Token Passing

Token Ring and IEEE 802.5 are the primary examples of token-passing networks Token-passing

networks move small frame called token around the network Possession of the token grants the

right to transmit If node receiving the token has no information to sendit simply passes the token

to the next end station Each station can hold the token for maximum period of time

If station possessing the token does have information to transmit it seizes the token alters one bit

of the token which turns the token into start-of-frame sequence appends the information it

wishes to transmit and finally sends this information to the next station on the ring While the

information frame is circling the ring there is no token on the network unless the ring supports early

token release so other stations wishing to transmit must wait Therefore collisions cannot occur in

Token Ring networks If early token release is supported new token can be released when frame

transmission is completed

The information frame circulates the ring until it reaches the intended destination station which

copies the information for further processing The information frame continues to circle the ring and

is finally removed when it reaches the sending station The sending station can check the returning

frame to see whether the frame was seen and subsequently copied by the destination

Unlike CSMAICD networks such as Ethernet token-passing networks are deterministic In other

it is calculate the maximum time that will before end station words possible to pass any will be able

to transmit This feature and several reliability features which are discussed in Fault Management

Mechanisms later in this chapter make Token Ring networks ideal for applications where delay

must be predictable and robust network operation is important Factory automation environments

are examples of such applications

6-2 Internetworking Technology Overview Physical Connections

Physicab Connections

IBM Token Ring network stations are directly connected to MSAUs which can be wired together

to form one large ring as shown in Figure 6-2 Patch cables connect MSAUs to adjacent MSAUs

Lobe cables connect MSAUs to stations MSAUs include bypass relays for removing stations from

the ring

Figure 6-2 IBM Token Ring Network Physical Connections

Priority System

that certain Token Ring networks use sophisticated priority system permits user-designated high- Token frames have two fields that control priority stations to use the network more frequently Ring

priority the priority field and the reservation field

value contained in token can seize Only stations with priority equal to or higher than the priority stations with that token Once the token is seized and changed to an information frame only

the token for the next priority value higher than that of the transmitting station can reserve pass of the around the network When the next token is generated it includes the higher priority reserving the after their station Stations that raise tokens priority level must reinstate previous priority

transmission is complete

Token Ring/IEEE 802.5 6-3 Fault Management Mechanisms

FauR Management Mechaffisms

Token Ring networks employ several mechanisms for detecting and compensating for network

faults For example one station in the Token Ring network is selected to be the active monitor This

which can be station the station potentially any on network acts as centralized source of timing

information for other ring stations and performs variety of ring maintenance functions One of

these functions is the removal of continuously circulating frames from the ring When sending

device its frame continue circle fails may to the ring This can prevent other stations from

their frames and transmitting own essentially lock up the network The active monitor can detect such them from the frames remove ring and generate new token

The IBM Token networks Ring star topology also contributes to overall network reliability Since

all information in Token Ring network is seen by active MSAUs these devices can be programmed

to check for and problems selectively remove stations from the ring if necessary

Token called Ring algorithm beaconing detects and tries to repair certain network faults

Whenever station detects serious problem with the network such as cable break it sends beacon frame The beacon frame defines failure domain which includes the station reporting the

failure its nearest active upstream neighbor NAUN and everything in between Beaconing initiates process called autoreconfiguration where nodes within the failure domain automatically

perform diagnostics in an attempt to reconfigure the network around the failed areas Physically the

MSAU can accomplish this through electrical reconfiguration

Frame Format

Token Ring networks define two frame types tokens and data/command frames Both formats are

shown in Figure 6-3

Data/command frame Field length nbytes

Start Access Frame Destination End Source address Data FCS delimiter control control address delimiter

Token

Start Access End

delimiter control delimiter

Figure 6-3 IEEE 802.5/Token Ring Frame Formats

Tokens

Tokens are three bytes in length and consist of start delimiter an access control byte and an end delimiter

The start delimiter serves to alert each station to the arrival of token or data/command frame

This field includes signals that distinguish the byte from the rest of the frame by violating the

encoding scheme used elsewhere in the frame

6-4 Internetworking Technology Overview Frame Format

The access control byte contains the priority and reservation fields as well as token bit used to

differentiate token from data/command frame and monitor bit used by the active monitor to

determine whether frame is circling the ring endlessly

Finally the end delimiter signals the end of the token or data/command frame It also contains bits

to indicate damaged frame and frame that is the last in logical sequence

Data/Command Frames

frames Data/command frames vary in size depending on the size of the information field Data carry and information for upper-layer protocols command frames contain control information have no

data for upper-layer protocols

In data/command frames frame control byte follows the access control byte The frame control

byte indicates whether the frame contains data or control information In control frames this byte

information specifies the type of control

Following the frame control byte are the two address fields which identify the destination and

source stations As with IEEE 8023 addresses are six bytes in length

The data field follows the address fields The length of this field is limited by the ring token holding time which defines the maximum time station may hold the token

This field is filled the Following the data field is the frame check sequence FCS field by source

destination station recalculates station with calculated value dependent on the frame contents The

in transit If the frame is the value to determine whether the frame may have been damaged so discarded

As with the token the end delimiter completes the data/command frame

Token Ring/IEEE 802.5 6-5 Frame Format

6-6 Internetworking Technology Overview CHAPTER

Fiber Distributed Data nter1ace

Background

The Fiber Distributed Data Interface FDDI standard was produced by the ANSI X3T9 .5 standards

committee in the mid-i 980s During this period high-speed engineering workstations were

beginning to tax the capabilities of existing local-area networks LANs primarily Ethernet and

needed that could these workstations and their Token Ring new LAN was easily support new

distributed applications At the same time network reliability was becoming an increasingly

important issue as system managers began to migrate mission-critical applications from large

computers to networks FDDI was developed to fill these needs

After completing the FDDI specification ANSI submitted FDDI to the International Organization

for Standardization ISO ISO has created an international version of FDDI that is completely

compatible with the ANSI standard version

Today although FDDI implementations are not as common as Ethernet or Token Ring FDDI has

gained substantial following that continues to increase as the cost of FDDI interfaces diminishes

FDDI is frequently used as backbone technology as well as means to connect high-speed

computers in local area

TechnoHogy Bascs

transmission medium FDDI specifies 100-Mbpstoken-passing dual-ring LAN using fiber-optic

It defines the physical layer and media-access portion of the link layer and so is roughly analogous

to IEEE 802.3 and IEEE 802.5 in its relationship to the OSI reference model

networks Although it operates at faster speeds FDDI is similarin many ways to Token Ring The two

share many features including topology ring media-access technique token passing reliability features beaconing for example and others Refer to Chapter Token Ring/IEEE 802.5 for more information on Token Ring and related technologies

medium One of FDDIs most important characteristics is its use of optical fiber as transmission does Optical fiber offers several advantages over traditional copper wiring including security fiber

emit electrical that is to electrical interference not signals can be tapped reliability fiber immune

and speed optical fiber has much higher throughput potential than copper cable

multimode FDDI defines use of two types of fiber single mode sometimes called monomode and

Modes be of bundles of the fiber at Single-mode can thought as light rays entering particular angle fiber allows fiber allows only one mode of light to propagate through the fiber while multimode

multiple modes of light to propagate through the fiber Because multiple modes of light propagating them to through the fiber may travel different distances depending on the entry angles causing arrive at the destination at different times phenomenon called modal dispersion singlemOde to fiber Due fiber is capable of higher bandwidth and greater cable run distances than multimode

7-1 Data interface Fiber Distributed FOOl Specifications

these characteristics single-mode fiber is often used for campus backbones while multimode fiber is often used for workgroup connectivity Multimode fiber uses light-emitting diodes LEDs as the

light-generating devices while single-mode fiber generally uses lasers

FDW Specfcatons

FDDI is defined four by separate specifications see Figure 7-1

Media Access Control MACDefines how the medium is accessed including frame format

token handling addressing algorithm for calculating cyclic redundancy check value and error

recovery mechanisms

Physical Layer Protocol Defines data encoding/decoding procedures clocking requirements framing and other functions

Physical Layer Medium DependentDefines the characteristics of the transmission medium

including the fiber-optic link power levels bit error rates optical components and connectors

Station ManagementDefines the FDDI station configuration ring configuration and ring

control features including station insertion and removal initialization fault isolation and

recovery scheduling and collection of statistics

Logical Link Control

Media Access Control

Station FDDI Physical Layer Protocol Management standards

Physical Layer Medium

Figure 1-1 FDDI Standards

Physca Connections

FDDI specifies the use of dual rings Traffic on these rings travels in opposite directions Physically

the rings consist of two or more point-to-point connections between adjacent stations One of the

two FDDI rings is called the primary ring the other is called the secondary ring The primary ring

is used for data transmission while the secondary ring is generally used as backup

Class or single-attach stations SAS attach to one ring Class or dual-attach stations DAS

attach to both rings SASs are attached to the primary ring through concentrator which provides

connections for multiple SASs The concentrator ensures that failure or power down of any given

SAS does not interrupt the ring This is particularly useful when PCs or similar devices that power

on and off frequently connect to the ring

7-2 Internetworking Technology Overview Traffic Types

typical FDDI configuration with both DASs and SASs is shown in Figure 7-2

Figure 7-2 FDDI Nodes DAS SAS and Concentrator

Each FDDI DAS has two portsdesignated and These ports connect the station to the dual FDDI

ring Therefore each port provides connection for both the primary and the secondary ring as

shown in Figure 7-3

FDDI DAS

Figure 7-3 FDDI DAS Ports

Traffic Types

it ideal for of different FDDI supports real-time allocation of network bandwidth making variety

of traffic and application types FDDI provides this support by defining two types synchronous

asynchronous Synchronous traffic can consume portion of the lOO-Mbps total bandwidth of an

FDDI network while asynchronous traffic can consume the rest Synchronous bandwidth is

allocated to those stations requiring continuous transmission capability Such capability is useful for

transmitting voice and video information for example Other stations use the remaining bandwidth

asynchronously FDDIs SMT specification defines distributed bidding scheme to allocate FDDI bandwidth

scheme Each station is Asynchronous bandwidth is allocated using an eight-level priority assigned

where stations an asynchronous priority level FDDI also permits extended dialogues may mechanism lock out temporarily use all asynchronous bandwidth FDDIs priority can essentially

stations that cannot use synchronous bandwidth and have too low an asynchronous priority

Fiber Distributed Data Interface 7-3 Fault-Tolerant Features

FauRToerant Features

FDDI provides number of fault-tolerant features The primary fault-tolerant feature is the dual ring

If station on the dual ring fails or is powered down or if the cable is damaged the dual ring is

into in In this automatically wrapped doubled back onto itself single ring as shown Figure 7-4

figure when Station fails the dual ring is automatically wrapped in Stations and forming

single ring Although Station is no longer on the ring network operation continues for the

remaining stations

Station

Failed station

Station

Figure 14 Station Failure Ring Recovery Configuration

Figure 7-5 shows how FDDI compensates for wiring failure Stations and wrap the ring within

themselves when wiring between them fails

7-4 Internetworking Technology Overview Fault-Tolerant Features

Station

Station Station

Station

Figure 1-5 Failed Wiring Ring Recovery Configuration

the of failures When two ring failures As FDDI networks grow possibility multiple ring grows the into two occur the ring will be wrapped in both cases effectively segmenting ring separate rings that cannot communicate with each other Subsequent failures cause additional ring segmentation

be used to failed stations from Optical bypass switches can prevent ring segmentation by eliminating the ring This is shown in Figure 7-6

Fiber Distributed Data Interface 7-5 Frame Format

Station

Optical bypass switch

bypassed configuration

Station Station

Figure 7-6 Lisa of Optical Bypass Switch

Critical devices such as routers or mainframe hosts can use another fault-tolerant technique called dual additional homing to provide redundancy and help guarantee operation In dual-homing

situations the critical device is attached to two concentrators One pair of concentrator links is

declared the active the other link pair is declared passive The passive link stays in backup mode

until the primary link or the concentrator to which it is attached is determined to have failed When

this occurs the passive link is automatically activated

Frame Format

FDDI frame formats shown in Figure 7-7 are similar to those of Token Ring

7-6 Internetworking Technology Overview Frame Format

Data frame

Figure 1-1 FODI Frame Format

The preamble prepares each station for the upcoming frame

The start delimiter indicates the beginning of the frame It consists of signaling patterns that differentiate it from the rest of the frame

The frame control field indicates the size of the address fields whether the frame contains asynchronous or synchronous data and other control information

As with Ethernet and Token Ring FDDI addresses are six bytes The destination address field can contain unicast singular multicast group or broadcast every station address while the source address identifies the single station that sent the frame

The data field contains either information destined for an upper-layer protocol or control information

station As with Token Ring and Ethernet theframe check sequence FCSfield is filled by the source with calculated check value the contents The cyclic redundancy CRC dependent on frame destination station recalculates the value to determine whether the frame may have been damaged in transit If so the frame is discarded

The end delimiter contains nondata symbols that indicate the end of the frame

The frame status field allows the source station to determine if an error occurred and if the frame was recognized and copied by receiving station

Fiber Distributed Data Interface 7-1 Frame Format

1-8 Internetworking Technology Overview AP

HghSpeed Seriag Interface

Background

trend Local-area networks Increasing communication speeds are an undeniable networking LANs Local have recently moved into the 100-Mbps range with Fiber Distributed Data Interface FDDI

and distributed applications driving these speed increases include imaging video todays client-

will continue to drive rates in server data transmission applications Faster computer platforms up

the local environment as they make new high-speed applications possible

match the Higher-throughput wide-area network WAN pipes have been developed to ever-

increasing LAN speeds and to allow mainframe channel extension over WANs WAN technologies Service Network such as Frame Relay Switched Multimegabit Data SMDS Synchronous Optical

SONET and Broadband Integrated Services Digital Network Broadband ISDN or simply

to ensure that WANs are not BISDN take advantage of new digital and fiber-optic technologies communication areas See 13 significant bottleneck in end-to-end over large geographic Chapter information Frame Relay and Chapter 14 Switched Multimegabit Data Service for more on Frame Relay and SMDS respectively

and the wide-area data terminal With higher speeds being achieved in both the local environments these equipment DTE/data circuit-terminating equipment DCE interface that could bridge two worlds without becoming bottleneck became critical need Classical DTEIDCE interface that standards such as RS-232 and V.35 are not capable of supporting T3 digital WAN service

clear that DTEIDCE operates at 45 Mbps or similar rates By the late 1980s it was new protocol was needed

Cisco and The High-Speed Serial Interface HSSI is DTE/DCE interface developed by Systems links The HSSI T3plus Networking to address the need for high-speed communication over WAN HSSI So 150 of specification is available to any organization wishing to implement far over copies are the specification have been distributed and dozens of companies have implemented or currently

implementing an HSSI solution In less than three years HSSI has become de facto industry

standard

National Standards Institute Electronic Industries Association HSSI is now in the American ANSI

for formal standardization It has moved into the Consultative EIAITIA TR3O .2 committee recently International for Committee for International Telegraph and Telephone CCITT and Organization these bodies Standardization ISO organizations as well and is expected to be standardized by

TechnoHogy Bascs

to the HSSI defines both the electrical and the physical DTE/DCE interface It therefore corresponds

technical characteristics are summarized in physical layer of the OSI reference model HSSI Table 8-1

High-Speed Serial Interface 8-1 Technology Basics

Table 8-1 HSSI Technical Characteristics

Characteristic Value

Maximum signaling rate 52 Mbps

Maximum cable length 50 feet

Number of connector pins 50

Interface DTE-DCE

Electrical technology Differential ECL

Typical power consumption 610 mW

Topology Point-to-point

Cable type Shielded twisted pair

The maximum signaling rate of HSSI is 52 Mbps At this rate HSSI can handle the T3 speeds

of of fast the Channel -1 45 Mbps many todays WAN technologies Office OC-l speeds 52 of the and Mbps synchronous digital hierarchy SDH can easily provide high-speed connectivity between LANs such as Token Ring and Ethernet

The use of differential HSSI achieve data and emitter-coupled logic ECL helps high rates low noise levels has been ECL used in Cray interfaces for years and is also specified by the ANSI High- Parallel Performance Interface HIPPI communications standard for supercomputer LAN communications ECL is off-the-shelf technology that permits excellent retiming on the receiver

resulting in reliable timing margins

The flexibility of HSSIs clock and data signaling protocol makes user or vendor bandwidth allocation possible The DCE controls the clock by changing its speed or by deleting clock pulses

In this the way DCE can allocate bandwidth between applications For example PBX may require particular amount of bandwidth router another amount and channel extender third amount Bandwidth allocation is key to making T3 and other broadband services affordable and popular

HSSI uses subminiature FCC-approved 50-pin connector that is smaller than its V.35 counterpart To reduce the need for male-male and female-female adapters HSSI cable connectors are specified

as male The HSSI cable the uses same number of pins and wires as the Small Computer Systems

Interface SCSI-2 cable but the HSSI electrical specification is tighter

For high level of diagnostic input HSSI provides four loopback tests These tests are shown in

8-1 The first local cable Figure provides test as the signal loops back once it reaches the DTE port

The second test reaches the line of the local port DCE The third test reaches the line port of the

remote the fourth test is DCE Finally DCE-initiated test of the DTEs DCE port

8-2 Internetworking Technology Overview Technology Basics

DIE Local DCE

Cable test

DIE Local DCE

DCE test

Remote Local DCE DCE

Telco line test WAN ______

DIE Local DCE

DlEtest

Figure 8-1 HSSIs Four Loopback Tests

and The control is HSSI assumes peer-to-peer intelligence in the DCE DTE protocol simplified

with control available Both signals must be just two signals required DTE and DCE available

asserted before the data circuit is valid The DCE and DTE are expected to be able to manage the

networks behind their interfaces Reducing the number of control signals improves circuit reliability

by reducing the number of circuits that can fail

High-Speed Serial Interface 8-3 Technology Basics

8-4 Internetworking Technology Overview H-A 1- ER

Point4oPoint Protoco

Background

international research institutions In the late 980s the Internet large network connecting many

to growth in government agencies universities and private businesses began experience explosive Protocol The vast of these hosts were the number of hosts supporting the Internet IP majority Ethernet the most Most connected to local-area networks LANs of various types being common networks such as of the other hosts were connected through wide-area WANs X25-style public connected with that data networks PDNs Relatively few of these hosts were simple point-to-point oldest methods of data communications and is serial links Yet point-to-point links are among the connections For asynchronous RS-232-C almost every host supports point-to-point example

interfaces are essentially ubiquitous

the lack of standard Internet One reason for the small number of point-to-point IP links was Point-to-Point Protocol was to solve this problem In encapsulation protocol The PPP designed of IP links addition to solving the problem of standardized Internet encapsulation over point-to-point and of IF PPP was also designed to address other issues including assignment management

bit-oriented network protocol addresses asynchronous startlstop and synchronous encapsulation detection and negotiation for such multiplexing link configuration link quality testing error option and data PPP addresses capabilities as network-layer address negotiation compression negotiation Control Protocol and family of Network these issues by providing an extensible Link LCP and facilities PPP Control Protocols NCPs to negotiate optional configuration parameters Today besides IPX and DECnet supports other protocols IP including

PPP Components

serial links It has three main PPP provides method for transmitting datagrams over point-to-point

components

linksPPP the Data Link method for encapsulating datagrams over serial uses High-Level links See Control HDLC protocol as basis for encapsulating datagrams over point-to-point Link Control and Derivatives for more information on HDLC Chapter 11 Synchronous Data

data-link connection An extensible LCP to establish configure and test the

PPP is family of NCPs for establishing and configuring different network-layer protocols of designed to allow the simultaneous use multiple network-layer protocols

Point-to-Point Protocol 9-1 General Operation

GeneraH Operaton

In order to establish communications over point-to-point link the originating PPP first sends LCP

frames to configure and optionally test the data link After the link has been established and

optional facilities have been negotiated as needed by the LCP the originating PPP sends NCP frames

to choose and configure one or more network-layer protocols Once each of the chosen network-

layer protocols has been configured packets from each network-layer protocol can be sent over the

link The link will remain configured for communications until explicit LCP or NCP frames close

the link or until some external event occurs for example an inactivity timer expires or user intervenes

PhysicaD1ayer Requrements

PPP is capable of operating across any DTE/DCE interface for example EIA RS-232-C ETA

RS-422 ETA RS-423 and CCITT V.35 The only absolute requirement imposed by PPP is the

provision of duplex circuit either dedicated or switched that can operate in either an asynchronous

or synchronous bit-serial mode transparent to PPP link-layer frames PPP does not impose any

restrictions regarding transmission rate other than those imposed by the particular DTE/DCE

interface in use

The PPP Link Layer

PPP uses the principles terminology and frame structure of the International Organization for Standardizations ISOs HDLC procedures ISO 3309-1979 as modified by ISO

33091984/PDADI Addendum Startlstop transmission ISO 3309-1979 specifies the HDLC frame structure for use in synchronous environments ISO 3309 1984/PDAD1 specifies proposed modifications to ISO 3309-1979 to allow its use in asynchronous environments The PPP control

procedures use the definitions and control field encodings standardized in ISO 4335-1979 and ISO 4335-1979/Addendum 1-1979

The PPP frame format appears in Figure 9-1

Field length

in bytes Variable or

Flag Control Protocol Data Address FCS

Figure 9-1 PPP Frame Format

is Theflag sequence single byte and indicates the beginning or end of frame The flag sequence

consists of the binary sequence 01111110

The address field is single byte and contains the binary sequence 11111111 the standard broadcast

address PPP does not assign individual station addresses

The control field is single byte and contains the binary sequence 00000011 which calls for

transmission of user data in an unsequenced frame connectionless link service similar to that of Link Control Logical LLC Type is provided Refer to Chapter 11 Synchronous Data Link Control and Derivatives for more information on LLC types and frame types

9-2 Internetworking Technology Overview The PPP Link Control Protocol

The protocol field is two bytes and its value identifies the protocol encapsulated in the information

field of the frame The most up-to-date values of the protocol field are specified in the most recent Assigned Numbers Requestfor Comments RFC

The data field is zero or more bytes in length and contains the datagram for the protocol specified

in the protocol field The end of the information field is found by locating the closing flag sequence

and allowing two bytes for the FCS field The default maximum length of the information field is

1500 bytes By prior agreement consenting PPP implementations can use other values for the

maximum information field length

The frame check sequence FCS field is normally 16 bits two bytes By prior agreement detection consenting PPP implementations can use 32-bit four-byte FCS for improved error

The LCP can negotiate modifications to the standard PPP frame structure However modified

frames will always be clearly distinguishable from standard frames

The PPP Lnk Contro Protoco

The PPP LCP provides method of establishingconfiguringmaintaining and terminating the point-

connection four distinct to-point LCP goes through phases

and Link establishment configuration negotiationBefore any network-layer datagrams for connection and example IP can be exchanged LCP must first open the negotiate configuration frame has been both parameters This phase is complete when configuration acknowledgment sent and received

Link quality determinationLCP allows an optional link quality determination phase following

the link establishment and configuration negotiation phase In this phase the link is tested to

This is determine if the link quality is sufficient to bring up network-layer protocols phase

until this is optional LCP can delay transmission of network-layer protocol information phase

completed

finished the link Network-layer protocol configuration negotiation Once LCP has quality

the determination phase network-layer protocols can be separately configured by appropriate

it informs the NCP and can be brought up and taken down at any time If LCP closes the link

network-layer protocols so that they may take appropriate action

done the Link terminationLCP can terminate the link at any time This will usually be at

carrier the request of user but can happen because of physical event such as the loss of or

expiration of an idle-period timer

There are three classes of LCP frames

Link establishment framesUsed to establish and configure link

Link termination frames Used to terminate link

Link maintenance frames Used to manage and debug link

These frames are used to accomplish the work of each of the LCP phases

Point-to-Point Protocol 9-3 The PPP Link Control Protocol

9-4 Internetworking Technology Overview H-A 10

Integrated Services Digftal Network

Background

Services Network refers to set of services that are Integrated Digital ISDN digital becoming network that available to end users ISDN involves the digitization of the telephone so voice data end from text graphics music video and other source material can be provided to users single worldwide network end-user terminal over existing telephone wiring Proponents of ISDN imagine used and of much like the present telephone network except that digital transmission is variety new

services are available

and and ISDN is an effort to standardize subscriber services user/network interfaces network

level internetwork capabilities Standardizing subscriber services attempts to ensure of and intemational compatibility Standardizing the user/network interface stimulates development intemetwork marketing of these interfaces by third-party manufacturers Standardizing network and

that ISDN networks capabilities helps achieve the goal of worldwide connectivity by ensuring easily communicate with one another

IV additional ISDN applications include high-speed image applications such as Group facsimile

file and video telephone lines in homes to serve the telecommuting industry high-speed transfer

conferencing Voice of course will also be popular application for ISDN

North Many carriers are beginning to offer ISDN under tariff In America large local-exchange carriers LECs are beginning to provide ISDN service as an alternative to the connections

that bulk wide-area digital carrier facilities provided by telephone companies currently carry

telephone service WATS services

Components

ISDN components include terminals terminal adapters TAs network-termination devices line- termination equipment and exchange-termination equipment ISDN terminals come in two types Non-ISDN terminals Specialized ISDN terminals are referred to as terminal equipment type TEl referred terminal such as DTE that predate the ISDN standards are to as equipment type TE2

TE1s connect to the ISDN network through four-wire twisted-pair digital link TB2s connect to the

either be stand-alone device or ISDN network through terminal adapter The ISDN TA can

board inside the TE2 If the TE2 is implemented as stand-alone device it connects to the TA via

standard physical-layer interface for example EIA-232-C V.24 or V.35

Beyond the TEl and TE2 devices the next connection point in the ISDN network is the network

device These are network termination type NT1 or network termination type NT2 termination devices that connect the four-wire subscriber wiring to the conventional two-wire local device In most other loop In North America the NT1 is customer premises equipment CPE parts

The NT2 is more of the world the NT1 is part of the network provided by the carrier complicated

Integrated Services Digital Network 10-1 Services

device typically found in digital private branch that exchanges PBXs performs layer and

protocol functions and concentration services An NT1/2 device also exists it is single device that combines the functions of an NT1 and an NT2

number of reference points are in ISDN These reference specified points define logical interfaces between functional such TAs groupings as and NTis ISDN reference points include the reference point between non-ISDN and equipment TA the reference point between user terminals and the NT2 the reference point between Nil and NT2 devices and the reference point between

NT1 devices and line-termination in the carrier equipment network The reference point is relevant in only North America where the Nil function is not provided by the carrier network

sample ISDN configuration is shown in 10-1 This Figure figure shows three devices attached to an ISDN switch at the central office Two of these devices are ISDN-compatible so they can be attached an reference through point to Ni2 devices The third device astandard non-ISDN telephone attaches through the reference point to TA Any of these devices could also attach to NT1/2 device which would replace both the NT1 and the NT2 And although they are not shown similar user stations are attached to the right-most ISDN switch

TE2 device

standard telephone

Figure 10-1 Sample ISON Configuration

Se rv es

ISDNs Basic Rate Interface BRI service offers two channels and one channel 2BD BRI B-channel service at 64 and is operates kbps meant to carry user data BRI D-channel service

operates at 16 kbps and is meant to control carry and signaling information it although can support user data transmission under certain circumstances The channel signaling protocol comprises layers through of the OSI reference model BRI also provides for framing control and other

overhead bringing its total bit rate to 192kbps The BRJ physical layer specification is CCITT 1.430

10-2 Internetworking Technology Overview Layer

ISDN Primary Rate Interface PRI service offers 23 channels and one channel in North America and Japan yielding total bit rate of 1.544 Mbps the PRI channel runs at 64 kbps

ISDN PRI in Europe Australia and other parts of the world provides 30 plus one 64-kbps

channel and total interface rate of 2.048 Mbps The PRI physical-layer specification is CCITT 1.431

Layer

ISDN physical-layer layer frame formats differ depending on whether the frame is outbound

from terminal to network or inbound from network to terminal Both physical-layer interfaces

are shown in Figure 10-2 The frames are 48 bits long of which 36 bits represent data The bits used contention provide synchronization The bits adjust the average bit value The bits are for

resolution when several terminals on passive bus contend for channel The bit activates

devices The bits have not yet been assigned The Bl B2 and bits are for user data

Field length inbits 11 11111 111 111

B1 B2 Bi Ff LDL LDL

NT frame network to terminal

Field length In bits 11 11111 111 111

B2 B2 FL Bi EDS Bi EDS

TE frame terminal to network

Activation bit

Bi Bi channel bits

B2 B2 channel bits

channel bits 4000 frames/sec 16 kbps

Echo of previous bit

Framing bit

Load balancing Spare bit

Figure 10-2 ISDN Physical-Layer Frame Formats

circuit In this collisions Multiple ISDN user devices can be physically attached to one configuration determine can result if two terminals transmit simultaneously ISDN therefore provides features to E-bit link contention When an NT receives bit from the TE it echoes back the bit in the next transmitted bit position The TE expects the next bit to be the same as its last

Terminals cannot transmit into the channel unless they first detect specific number of ones

If the detects bit in the echo indicating no signal corresponding to pre-established priority TE This channel that is different from its bits it must stop transmitting immediately simple time After successful technique ensures that only one terminal can transmit its message at one

the terminal has its reduced it to detect more continuous message transmission priority by requiring

Integrated Services Digital Network 10-3 Layer

ones before transmitting Terminals may not raise their priority until all other devices on the same

line have had an opportunity to send message Telephone connections have higher priority than

all other services and signaling information has higher priority than nonsignaling information

Layer

Layer of the ISDN signaling protocol is LinkAccess Procedure channel also known as LAPD

LAPD is similar to High-Level Data Link Control HDLC and Link Access Procedure Balanced LAPB see Chapter 11 Synchronous Data Link Control and Derivatives and Chapter 12

.25 for more information on these protocols As LAPD acronym expansion indicates it is

used across the channel to ensure that control and signaling information flows and is received

properly LAPDs frame format see Figure 10-3 is very similar to that of HDLC and like HDLC

LAPD uses supervisory information and unnumbered frames The LAPD protocol is formally

specified in CCITT Q.920 and CCITT Q921

Field length

in bytes Variable

SAPI Service access point identifier bits C/R Command/response bit

EA Extended bits addressing CO TEl Terminal identifier endpoint Cl

Figure 10-3 LAPD Frame Format

The LAPD flag and control fields are identical to those of HDLC The LAPD address field can be

either one or two bytes long If the extended address bit of the first byte is set the address is one byte

if it is not set the address is two bytes The first address field byte contains the service access point

identUler SAPI which identifies the portal at which LAPD services are provided to layer The

C/R bit indicates whether the frame contains command or response The terminal end-point

identifier TEl field identifies either single terminal or multiple terminals TEl of all ones indicates broadcast

Layer

Two layer specifications are used for ISDN signaling CCITT 1.450 also known as CCITT Q.930

and CCITT 1.451 also known as CCITT .931 Together these protocols support user-to-user

circuit-switched and packet-switched connections variety of call establishment call termination

information and miscellaneous messages are specified including SETUP CONNECT RELEASE

USER INFORMATION CANCEL STATUS and DISCONNECT These messages are

10-4 Internetworking Technology Overview Layer

functionally similar to those provided by the X.25 protocol see Chapter 12 X.25 for more information Figure 1O-4from CCITT 1.451 shows the typical stages of an ISDN circuit-switched call

Router Calling Calling Called Called Called

call DTE DCE DCE DTE router

Pick up

Set up ACK

Call proceethn

Ringing lertiflg Aterting Pick up Connect

ConnecL_-i

Information Flow

Flow Information FloW Information

Disconnect

Release

leae complete Release complete

Figure 10-4 ISDN Circuit-Switched Call Stages

Integrated Services Digital rJetwork 10-5 Layer

10-6 Internetworking Technology Overview CHAPTER 11

Sync ron us ata Link Contro Derivatives

Background

in the mid-i 970s for in IBM developed the Synchronous Data Link Control SDLC protocol use of breed Systems Network Architecture SNA environments SDLC was the first an important new

of link-layer protocols based on synchronous bit-oriented operation Compared to synchronous

character-oriented for example Bisync from IBM and synchronous byte-count-oriented protocols

for example Digital Data Communications Message Protocol DDCMP from Digital Equipment and often faster Corporation bit-oriented synchronous protocols are more efficient more flexible

International After developing SDLC IBM submitted it to various standards committees The Link Control Organization for Standardization ISO modified SDLC to create the High-Level Data HDLC protocol The Consultative Committee for International Telegraph and Telephone CCITT Link subsequently modified HDLC to create Link Access Procedure LAP and then Access Procedure Balanced LAPB The Institute of Electrical and Electronic Engineers IEEE modified domain HDLC to create IEEE 802.2 Each of these protocols has become important in its own SDLC

remains SNAs primary link-layer protocol for wide-area network WAN links

Technoogy Basics

of link and It be used with and SDLC supports variety types topologies can point-to-point

and unbounded and transmission facilities multipoint links bounded media half-duplex full-duplex

and circuit-switched and packet-switched networks

SDLC identifies two types of network nodes

PrimaryControls the operation of other stations called secondaries The primary polls the

secondaries in predetermined order Secondaries can then transmit if they have outgoing data

links and the link while it is The primary also sets up and tears down manages operational

SecondaryAre controlled by primary Secondaries can only send information to the primary

but cannot do this unless the primary gives permission

basic SDLC primaries and secondaries can be connected in four configurations

Point-to-pointInvolves only two nodes one primary and one secondary

secondaries MultipointInvolves one primary and multiple

Synchronous Data Link Control and Derivatives 11-1 Frame Format

LoopInvolves ioop topology with the primary connected to the first and last secondaries Intermediate secondaries pass messages through one another as they respond to the primarys

requests

Hub go-aheadInvolves an inbound and an outbound channel The primary uses the outbound

channel to communicate with the secondaries The secondaries use the inbound channel to

communicate with the primary The inbound channel is daisy-chained back to the primary

through each secondary

Frame Format

The SDLC frame appears in Figure 11-1

Field length

in bytes or or Variable

Flag Address Control Data FCS Flag

Information

frame format

Receive Send Poll sequence sequence number final number

Supervisory frame format

Receive Poll Function sequence code number final

Unnumbered frame format

Function Poll Function code final code

Figure 11-1 SLJLC Frame Format

As the frames bounded figure shows SDLC are by unique flag pattern The address field always

contains the address of the involved secondary in the current communication Since the primary is either the communication source or destination there is no need to include the primarys address

it is already known by all secondaries

11-2 Internetworking Technology Overview Frame Format

The control field uses three different formats depending on the type of SDLC frame used The three

SDLC frames are described as follows

Information frames These frames carry upper-layer information and some control

information Send and receive sequence numbers and the poii final P/F bit perform flow and

error control The send sequence number refers to the number of the frame to be sent next The

receive sequence number provides the number of the frame to be received next Both the sender

and the receiver maintain send and receive sequence numbers The primary uses the P/F bit to

tell the secondary whether it requires an immediate response The secondary uses this bit to tell the primary whether the current frame is the last in its current response

Supervisory framesThese frames provide control information They request and suspend

transmission report on status and acknowledge the receipt of frames They do not have an information field

framesThese Unnumbered frames as the name suggests are not sequenced They are used control for control purposes For example they may specify either one- or two-byte field initialize secondaries and do other similar functions They may have an information field

The frame check sequence FCS precedes the ending flag delimiter The FCS is usually cyclic redundancy check CRC calculation remainder The CRC calculation is redone in the receiver If the result differs from the value in the senders frame an error is assumed

typical SDLC-based network configuration appears in Figure 11-2 As illustrated an IBM establishment controller formerly called cluster controller in remote site connects to dumb terminals and to Token Ring network In local site an IBM host connects via channel attach techniques to an IBM front-end processor FEP which can also have links to local Token Ring local-area networks LANs and an SNA backbone The two sites are connected through an SDLC based 56-kbps leased line

Synchronous Data Link Control and Derivatives 11-3 Derivative Protocols

Local site

Remote site

Figure 11-2 Typical SDLC-liased Network Configuration

Dervatve Protocos

the fact that it omits Despite several features used in SDLC HDLC is generally considered to be

compatible superset of SDLC LAP is subset of HDLC LAPB was created to ensure ongoing

compatibility with HDLC which had been modified in the early l980s IEEE 802.2 is modification

of HDLC for LAN environments Qualified Logical Link Control QLLC is link-layer protocol

defined by IBM that allows SNA data to be transported across X.25 networks

shares HDLC SDLCs frame format and HDLC fields provide the same functionality as those in

SDLC Also like SDLC HDLC supports synchronous full-duplex operation

HDLC differs from SDLC in several minor ways First HDLC has an option for 32-bit checksum

And unlike SDLC HDLC does not support the loop or hub go-ahead configurations

11-4 Internetworking Technology Overview Derivative Protocols

difference The major between HDLC and SDLC is that SDLC supports only one transfer mode

while HDLC supports three The three HDLC transfer modes are as follows

Normal response mode NRM This transfer mode is used by SDLC In this mode secondaries

cannot communicate with primary until the primary has given permission

Asynchronous response mode ARM This transfer mode allows secondaries to initiate

communication with primary without receiving permission

Asynchronous balanced mode ABM ABM introduces the combined node combined node

can act as primary or secondary depending on the situation All ABM communication is

between multiple combined nodes In ABM environments any combined station may initiate data transmission without from other permission any

LAPB

is best known for its in the shares the frame LAPB presence X.25 protocol stack LAPB same format

frame types and field functions as SDLC and HDLC Unlike either of these however LAPB is stations restricted to the ABM transfer mode and so is appropriate only for combined Also LAPB circuits can be established by either the data terminal equipment DTE or the data circuit-

terminating equipment DCE The station initiating the call is determined to be the primary while

the responding station is the secondary Finally LAPB use of the P/F bit is somewhat different from

that of the other protocols See Chapter 12 X.25 for details on LAPB

IEEE 802.2

IEEE 802.2 is often referred to as Logical Link Control LLC It is extremely popular in LAN

environments where it interoperates with protocols such as IEEE 802.3 IEEE 802.4 and IEEE 802.5

IEEE 802.2 offers three types of service Type provides unacknowledged connectionless service

Type provides connection-oriented service Type provides acknowledged connectionless service

As an unacknowledged connectionless service LLC Type does not confirm data transfers Because

many upper-layer protocols such as Transmission Control Protocol/Internet Protocol TCP/IP offer reliable data transfer that can compensate for unreliable lower-layer protocols Type is commonly used service

LLC Type often called LLC2 service establishes logical connections between sender and

is found receiver and is therefore connection-oriented LLC2 acknowledges data upon receipt and in IBM communication systems

establish Although LLC Type service supports acknowledged data transfer it does not logical connections As compromise between the other two LLC services LLC Type is useful in factory

automation environments where error detection is important but context storage space for virtual

circuits is extremely limited

service End stations can support multiple LLC service types Class device supports only Type both Class II device supports both Type and Type service Class III devices support Type

and Type service while Class IV devices support all three types of service

The Upper-layer processes use IEEE 802.2 services through service access points SAPs IEEE

identifies the 802.2 header begins with destination service access point DSAP field which

receiving upper-layer process In other words after the receiving nodes IEEE 802.2 implementation

its identified in the field receives the completes processingthe upper-layer process DSAP remaining which data Following the DSAP address is the source service access point SSAP address

identifies the sending upper-layer process

Synchronous Data Link Control and Derivatives 11-5 Derivative Protocols

QLLc

the data link control that to data .25 QLLC provides capabilities are required transport SNA across

networks Together QLLC and X.25 replace SDLC in the SNA protocol stack

QLLC uses the packet-level layer layer of the .25 protocol stack To indicate that layer .25

packet must be handled by QLLC special bit called the qual/ler bit in the general format

ident/ler GFI of the layer X.25 packet-level header is set to one The SNA data is carried as user

data in Layer X.25 packets

For more information about the X.25 protocol stack see Chapter 12 X.25

11-6 Internetworking Technology Overview

CHAPTER 12

X25

Background

In the 1970s set of protocols was needed to provide users with wide-area network WAN

connectivity across public data networks PDNs PDNs such as TELENET and TYMNET had

achieved remarkable success but it was felt that protocol standardization would increase

and lower The result of subscription to PDNs by providing improved equipment compatibility cost

which is X.25 the ensuing development effort was group of protocols the most popular of

.25 formally referred to as the Consultative Committee for International Telegraph and Telephone

CCITT Recommendation X.25 was developed by the common carriers phone companies

is therefore essentially rather than any single commercial enterprise The specification designed to with the work well regardless of users system type or manufacturer Users contract common Services carriers to use their packet-switched networks PSNs and are charged based on PSN use

offered and charges levied are regulated by the Federal Communications Commission FCC

One of .25s unique attributes is its international nature .25 and related protocols are

administered by an agency of the United Nations called the International Telecommunications Union

ITU The CCITT is the ITU committee responsible for voice and data communications CCITT

members include the FCC the European Postal Telephone and Telegraph organizations the common

carriers and many computer and data communications companies As result X.25 is truly global standard

Technoogy Bascs

X.25 defines telephone network for data communications To begin communication one computer

calls another to request communication session The called computer can accept or.refuse the

connection If the call is accepted the two systems can begin full-duplex information transfer Either

side can terminate the connection at any time

interaction data terminal The X.25 specification defines point-to-point between equipment DTE

and data circuit-terminating equipment DCE DThs terminals and hosts in the users facilities connect to DCEs modems packet switches and other ports into the PDN generally located in the

carriers facilities which connect to packet switching exchanges PSEs or simply switches and

other DCEs inside PSN and ultimately to another DTE The relationship between the entities in

an X.25 network is shown in Figure 12-1

X.25 12-1 Technology Basics

PSN

Figure 12-1 X.25 Model

DTE can be terminal that does not implement the complete X.25 functionality DTE is

connected to DCE through translation device called packet assembler/disassembler PAD The

operation of the terminal-to-PAD interface the services offered by the PAD and the interaction between the PAD and the host are defined by CCITT Recommendations X.28 X.3 and X29

respectively

X.25 the reference model X.25 The specification maps to layers through of OSI Layer entities describes packet formats and packet exchange procedures between peer layer Layer defines .25 is implemented by Link Access Procedure Balanced LAPB LAPB packet framing

for the DTE/DCE link Layer X.25 defines the electrical and mechanical procedures for activating

and deactivating the physical medium connecting the DTE and the DCE This relationship is shown

in Figure 12-2 Note that layers and are also referred to as the ISO standards ISO 7776 LAPB

and ISO 8208 X.25 packet layer

Os X.25 reference model

User- Packet-

defined switching process network

X.25 4- Packet interface packet level

X.25 4- Frame interface frame level

X.25 Physical interface physical level

DTE DTE/DCE DCE

interface

Figure 12-2 X.25 and the OSI Reference Model

12-2 Internetworking Technology Overview Frame Format

End-to-end communication between DTEs is accomplished through bidirectional association

called virtual circuit Virtual circuits permit communication between distinct network elements number of intermediate through any nodes without the dedication of portions of the physical

medium that characterizes physical circuits Virtual circuits can either be permanent or switched

temporary Permanent virtual circuits are commonly called PVCs switched virtual circuits are called commonly SVCs PVCs are typically used for the most-often-used data transfers while SVCs

are used for sporadic data transfers Layer X.25 is concerned with end-to-end communication

involving both PVCs and SVCs

Once virtual circuit is established the DTE sends packet to the other end of the connection by

sending it to the DCE using the proper virtual circuit The DCE looks at the virtual circuit number

to determine how to route the packet through the X.25 network The layer X.25 protocol

multiplexes between all the DTEs served by the DCE on the destination side of the network and the

packet is delivered to the destination DTE

Frame Format

An X.25 frame is composed of series of fields as shown in Figure 12-3 Layer X.25 fields make

up an X.25 packet and include header and user data Layer X.25 LAPB fields include frame-

level control and the embedded addressing fields layer packet and frame check sequence FCS

Packet

Packet- User Layer data X.25 header

Frame level Layer Flag control and Data FCS Flag X.25 address

Frame 11

Layer Bit stream

Figure 12-3 X.25 Frame

Layer

channel The layer X.25 header is made up of generalformat identifier GET logical identifier the format of LCI and packet type identifier PIT The GFT is 4-bit field that indicates general

the packet header The LCT is 12-bit field that identifies the virtual circuit The LCI is locally

significant at the DTE/DCE interface In other words the PDN connects two logical chaelseach

circuit The PTI field with an independent LCI on two DTE/DCE interfaces to establish virtual

identifies one of X.25s 17 packet types

These Addressing fields in call setup packets provide source and destination DTE addresses are

used to establish the virtual circuits that constitute X.25 communication CCIII Recommendation

referred X.121 specifies the source and destination address formats X.121 addresses also to as

International Data Numbers or IDNs vary in length and can be up to 14 decimal digits long Byte

X.25 12-3 Frame Format

four in the call setup packet specifies the source DTE and destination DTE address lengths The first

code The DNIC is divided four digits of an IDN are called the data network identification DNIC

into two parts the first three digits specifying the country and the last specifying the PSN itself and used The remaining digits are called the national terminal number NTN are to identify the

specific DTE on the PSN The X.121 address format is shown in Figure 12-4

DNIC NTN

digits up to 10 digits btIs bits

Called DTE Calling DTE National

address address Country PSN terminal length length number

International Data Number

Figure 124 X.121 Address Format

The addressing fields that make up the X.121 address are only necessary when an SVC is used and

then only during call setup Once the call is established the PSN uses the LCI field of the data packet

header to specify the particular virtual circuit to the remote DTE

Layer X.25 uses three virtual circuit operational procedures

Call setup

Data transfer

Call clearing

Execution of these procedures depends on the virtual circuit type being used For PVC layer

X.25 is always in data transfer mode because the circuit has been permanently established If an SVC

is used all three procedures are used

Data transfer is effected by data packets Layer X25 segments and reassembles user messages if

they are too long for the circuits maximum packet size Each data packet is given sequence

number so error and flow control can occur across the DTE/DCE interface

Layer

Layer .25 is implemented by LAPB LAPB allows both sides the DTE and the DCE to initiate

communication with the other During information transfer LAPB checks that the frames arrive at

the receiver in the correct sequence and error-free

12-4 Internetworking Technology Overview Frame Format

As with similar three link-layer protocols LAPB uses frame format types

frameThese frames Information carry upper-layer information and some control

information for necessary full-duplex operation Send and receive sequence numbers and the

final bit flow poll P/F perform control and error recovery The send sequence number refers to the number of the frame current The receive sequence number records the number of the frame

to be received next In full-duplex conversation both the sender and the receiver keep send and receive numbers sequence The poii bit is used to force final bit message in response this is

used for detection error and recovery

Supervisory framesThese frames provide control information They request and suspend

transmission report on status and acknowledge the receipt of frames They do not have an information field

Unnumbered framesThese frames as the name suggests are not sequenced They are used

for control purposes For example they may initiate connection using standard or extended disconnect the windowing modulo versus 128 link report protocol error or similar functions

The LAPB frame is shown in Figure 12-5

Field length Variable

in bytes

Figure 12-5 LAPB Frame

fields delimit Theflag the LAPB frame Bit stuffing is used to ensure that the flag pattern does not

occur within the body of the frame

The address field indicates whether the frame carries command or response

The control field further of command and provides qualifications response frames and also indicates the frame format or frame function for example receiver ready or disconnect and the

send/receive sequence number

The data field carries data Its size and format upper-layer vary depending on the layer packet type

The maximum length of this field is set by agreement between PSN administrator and the

subscriber at subscription time

The FCS field ensures the integrity of the transmitted data

Layer

Layer X.25 uses the X.21 bis physical-layer protocol which is roughly equivalent to RS-232-C

X.21 bis was derived from CCITT Recommendations V.24 and V.28 which identify the interchange

circuits and electrical characteristics respectively of DTE to DCE interface X.2l bis supports

point-to-point connections speeds of up to 19.2 kbps and synchronous full-duplex transmission

over four-wire media The maximum distance between DTE and DCE is 15 meters

X.25 12-5 Frame Format

12-6 Internetworking Technology Overview CHAPTER 13

Frame ReOay

Background

Frame Relay was originally conceived as protocol for use over ISDN interfaces and initial

proposals to this effect were submitted to the Consultative Committee for International Telegraph

and Telephone CCITT in 1984 Work on Frame Relay was also undertaken in the American

National Standards Institute ANSIaccredited Ti Si standards committee in the United States

There was major development in Frame Relays history in 1990 when Cisco Systems StrataCom

Northern Telecom and Digital Equipment Corporation formed consortium to focus Frame Relay

technology development and accelerate the introduction of interoperable Frame Relay products This

consortium developed specification conforming to the basic Frame Relay protocol being discussed

in Ti Si and CCITT but extended it with features that provide additional capabilities for complex

internetworking environments These Frame Relay extensions are referred to collectively as the local

management interface LMI

Technoogy Bascs

Frame Relay provides packet-switching data communications capability that is used across the interface between devices user for example routers bridges host machines and network

equipment for example switching nodes User devices are often referred to as data terminal while equipment DTE network equipment that interfaces to DTE is often referred to as data

circuit-terminating equipment DCE The network providing the Frame Relay interface can be

either carrier-provided public network or network of privately owned equipment serving single

enterprise

As interface an to network Frame Relay is the same type of protocol as X.25 see Chapter 12

differs in its In X.25 However Frame Relay significantly from X.25 functionality and format

particular Frame Relay is more streamlined protocol facilitating higher performance and greater

efficiency

As an interface between user and network equipment Frame Relay provides means for statistically

data conversations virtual multiplexing many logical referred to as circuits over single physical

transmission link This contrasts with systems that use only time-division-multiplexing TDM

techniques for supporting multiple data streams Frame Relays statistical multiplexing provides

more flexible and efficient use of available bandwidth It can be used without TDM techniques or on

top of channels provided by TDM systems

Another important characteristic of Frame Relay is that it exploits the recent advances in wide-area

network WAN transmission technology Earlier WAN protocols such as X.25 were developed when

transmission and media links less analog systems copper were predominant These are much reliable

than the fiber media/digital transmission links available today Over links such as these link-layer

protocols can forego time-consuming error correction algorithms leaving these to be performed at

Frame Relay 13-1 LMI Extensions

higher protocol layers Greater performance and efficiency is therefore possible without sacrificing data integrity Frame Relay is designed with this approach in mind It includes cyclic redundancy check CRC algorithm for detecting corrupted bits so the data can be discarded but it does not include any protocol mechanisms for correcting bad data for example by retransmitting it at this

level of protocol

Another difference between Frame Relay and .25 is the absence of explicit per-virtual-circuit flow

control in Frame that Relay Now many upper-layer protocols are effectively executing their own flow control algorithms the need for this functionality at the link layer has diminished Frame Relay does not include flow therefore explicit control procedures that duplicate those in higher layers

Instead very simple congestion notification mechanisms are provided to allow network to inform

user device that the network resources are close to congested state This notification can alert

higher-layer protocols that flow control may be needed

Current Frame standards Relay address permanent virtual circuits PVCs that are administratively configured and managed in Frame Relay network Another type switched virtual circuits SVC5 has also been proposed The Integrated Services Digital Network ISDN signaling protocol is the proposed as means by which DTE and DCE will communicate to establish terminate and SVCs manage dynamically See Chapter 10 Integrated Services Digital Network for more

information on Both Ti Si and CCITT have work in include SVCs in ISDN progress to Frame Relay standards

LM Extensoris

In addition to the basic Frame Relay protocol functions for transferring data the consortium Frame

Relay specification includes LMI extensions that make supporting large complex intemetworks

easier Some LMI extensions are referred to as common and are expected to be implemented by

everyone who adopts the specification Other LMI functions are referred to as optional summary of the LMI extensions follows

Virtual circuit status messages common Provide communication and synchronization

between the network and the user device periodically reporting the existence of new PVCs and

the deletion of already existing PVCs and generally providing information about PVC integrity

Virtual circuit status messages prevent the sending of data into black holes that is over PVCs

that no longer exist

Multicasting optional Allows sender to transmit single frame but have it delivered by the

network to multiple recipients Thus multicasting supports the efficient conveyance of routing and protocol messages address resolution procedures that typically must be sent to many

destinations simultaneously

Global addressing optional Gives connection identifiers global rather than local significance be allowing them to used to identify specific interface to the Frame Relay network Global addressing makes the Frame Relay network resemble local-area network LAN in terms of address addressing resolution protocols therefore perform over Frame Relay exactly as they do over LAN

Simple flow control optionalProvides for an XON/XOFF flow control mechanism that

to the entire applies Frame Relay interface It is intended for those devices whose higher layers

cannot use the congestion notification bits and that need some level of flow control

13-2 Internetworking Technology Overview Frame Format

Frame Format

The Frame frame is shown in Relay Figure 13-1 Flags delimit the frames beginning and end the two Following leading flags are bytes of address information Ten bits of these two bytes make

the actual circuit ID the up called DLCI for data link connection identifier

Field length Variable

in bytes

Figure 13-1 Frame Relay Frame

The 10-bit DLCI value is the heart of the Frame Relay header It identifies the logical connection

that is into multiplexed the physical channel In the basic that is not extended by the LMI mode of

addressing DLCIs have local significance that is the end devices at two different ends of connection may use different DLCI to refer to that same connection Figure 13-2 provides an

of the example use of DLCIs in nonextended Frame Relay addressing

San Jose Pittsburgh

Figure 13-2 Frame Relay Addressing

In Figure 13-2 assume two PVCs one between Atlanta and Los Angeles and one between San Jose and Pittsburgh Los Angeles may refer to its PVC with Atlanta using DLCI 12 while Atlanta refers

to the same with 82 PVC DLCI Similarly San Jose may refer to its PVC with Pittsburgh using

DLCI 12 The network uses internal proprietary mechanisms to keep the two locally significant

PVC identifiers distinct

At the end of each DLCI is extended address byte an EA bit If this bit is one the current byte is the last DLCI All byte implementations currently use two-byte DLCI but the presence of the EA

bits means that longer DLCIs may be agreed upon and used in the future

The bit marked CIR following the most significant DLCI byte is currently not used

Frame Relay 13-3 LMI Message Format

Finally three bits in the two-byte DLCI are fields related to congestion control The forward explicit

congestion notification FECN bit is set by the Frame Relay network in frame to tell the DTE

receiving that frame that congestion was experienced in the path from source to destination The

backward notification explicit congestion BECN bit is set by the Frame Relay network in frames

traveling in the opposite direction from frames encountering congested path The notion behind

both of these bits is that the FECN or BECN indication can be promoted to higher-level protocol

that can take flow control action as appropriate FECN bits are useful to higher-layer protocols that

use receiver-controlled flow control while BECN bits are significant to those that depend on emitter-controlled flow control

The discard eligibility DE bit is set by the DTE to tell the Frame Relay network that frame has

lower importance than other frames and should be discarded before other frames if the network becomes short of resources Thus it represents very simple priority mechanism This bit is usually

set only when the network is congested

LM Message Format

The previous section described the basic Frame Relay protocol format for carrying user data frames The consortium Frame Relay specification also includes the LMI procedures LMI messages are sent

in frames distinguished by an LMI-specific DLCI defined in the consortium specification as

DLCI 1023 The LMI message format is shown in Figure 13-3

Field length

in bytes Variable

FCS Flag

Figure 13-3 LMI Message Format

In LMI messages the basic protocol header is the same as in normal data frames The actual LMI

message begins with four mandatory bytes followed by variable number of information elements The format and TEs encoding of LMI messages is based on the ANSI T1S1 standard

The first of the mandatory bytes unnumbered information indicator has the same format as the

LAPB unnumbered frame indicator with the bit set to the information UI poll/final zero See

section in Layer Chapter 12 X.25 for more information on LAPB The next byte is referred

to the as protocol discriminator which is set to value that indicates LMI The third mandatory

byte call reference is always filled with zeros

The final is mandatory byte the message type field Two message types have been defined Status- allow enquiry messages the user device to inquire about network status Status messages respond to

status-enquiry messages Keepalives messages sent through connection to ensure that both sides

will continue to regard the connection as active and PVC status messages are examples of these

and are the common features that be of messages LMI are expected to part every implementation that conforms to the consortium specification

and Together status status-enquiry messages help verify the integrity of logical and physical links

This information is critical in routing environment because routing algorithms make decisions

based on link integrity

the Following message type field is some number of lEs Each IE consists of single-byte JE IE ident/ler an length field and one or more bytes containing actual data

13-4 Internetworking Technology Overview IMI Message Format

Global Addressing

In addition to the common LMI features there are several optional LMI extensions that are

extension is extremely useful in an internetworking environment The first important optional LMI

global addressing As noted earlier the basic nonextended Frame Relay specification only

supports values of the DLCI field that identify PVCs with local significance In this case there are

no addresses that identify network interfaces or nodes attached to these interfaces Because these

addresses do not exist they cannot be discovered by traditional address resolution and discovery

techniques This means that with normal Frame Relay addressing static maps must be created to tell

routers which DLCIs to use to find remote device and its associated internétwork address

The global addressing extension permits node identifiers With this extension the values inserted in

the DLCI field of frame are globally significant addresses of individual end-user devices for

example routers This is implemented as shown in Figure 13-4

San Jose Pittsburgh

DLCI 12 DLCI 13

OLCI 14 DLCI 15

Los Angeles

Figure 13-4 Global Addressing Exchange

send frame In Figure 13-4 note that each interface has its own identifier Suppose Pittsburgh must

field and sends to San Jose San Joses identifier is 12so Pittsburgh places the value 12 in the DLCI

the frame into the Frame Relay network At the exit point the DLCI field contents are changed by

the network to 13 to reflect the frames source node As each routers interface has distinct value

in as its node identifier individual devices can be distinguished This permits adaptive routing

complex environments

Global addressing provides significant benefits in large complex internetwork The Frame Relay

the its like No to network now appears to routers on periphery any LAN changes higher-layer

protocols are needed to take full advantage of their capabilities

Frame Relay 13-5 Network Implementation

Muticastig

is another valuable feature Multicast Multicasting optional LMI groups are designated by series of four reserved DLCI values 1019 to 1022 Frames sent by device using one of these reserved

DLCIs are replicated by the network and sent to all exit points in the designated set The multicasting

extension also defines LMI that devices of the messages notify user addition deletion and presence of multicast groups

In networks that take advantage of dynamic routing routing information must be exchanged among routers with many Routing messages can be sent efficiently by using frames multicast DLCI This

allows to be sent to messages specific groups of routers

Network mpementaton

Frame be used Relay can as an interface to either publicly available carrier-provided service or to network of privately owned equipment typical means of private network implementation is to

traditional equip multiplexers with Frame Relay interfaces for data devices as well as non-Frame

interfaces for Relay other applications such as voice and video-teleconferencing Figure 13-5 shows

this configuration

Frame Relay interface

Ti -Frame Relay MUXnterface

Non-Frame Relay interface

Video/teleconference

Ethernet

Figure 13-5 Hybrid Frame Relay Network

13-6 Internetworking Technology Overview Network Implementation

public Frame Relay service is deployed by putting Frame Relay switching equipment in the central offices of telecommunications carrier In this case users may realize economic benefits

traffic-sensitive relieved from charging rates and are from the work necessary to administer and maintain the network equipment and service

In either type of network the lines that connect user devices to the network equipment may operate

at speed selected from broad range of data rates Speeds between 56 kbps and Mbps are typical

although Frame Relay can support lower and higher speeds Implementations capable of operating over 45-Mbps DS3 links are expected to be available soon

Whether in public or private network the support of Frame Relay interfaces to user devices does not necessarily dictate that the Frame Relay protocol is used between the network devices No

standards for interconnecting equipment inside Frame Relay network currently exist Thus

traditional circuit-switching packet-switching or hybrid approach combining these technologies

can be used

Frame Relay 13-7 Network Implementation

13-8 Internetworking Technology Overview CHAPTER 14

Swftched Muftimegabft Data Service

Background

service for Switched Multimegabit Data Service SMDS is packet-switched datagram designed

wide-area data communications offers data that will be very high speed SMDS throughputs initially in in the 1- to 34-Mbps range and is being deployed in public networks by the carriers response to

two trends The first trend is the proliferation of distributed processing and other applications that

require high-performance networking The second trend is the decreasing cost and high-bandwidth

potential of fiber media making support of such applications over wide-area network WAN

viable

SMDS is described in series of specifications produced by Bell Communications Research

Beilcore and adopted by the telecommunications equipment providers and carriers One of these

which is the between user specifications describes the SMDS Interface Protocol SIP protocol and network device referred to as customer premises equipment or CPE SMDS equipment

The SIP is based on an IEEE standard protocol for metropolitan area networks MANs that is the

IEEE 802.6 Distributed Queue Dual Bus DQDB standard Using this protocol CPE such as routers

can be attached to an SMDS network and use SMDS service for high-speed intemetworking

Technogy Bascs

this to is Figure 14-1 shows an internetworking scenario using SMDS In figure access SMDS

provided over either 1.544-Mbps DS-1 or Digital Signal or 44.736-Mbps DS-3 or Digital fiber-based DS-l Signal transmission facility Although SMDS is usually described as service with access may be provided over either fiber or copper-based media sufficiently good error network and the customers characteristics The demarcation point between the carriers SMDS referred the subscriber network equipment is to as interface SNI

Switched Multimegahit Data Service 14-1 Addressing

Ethernet

DS-3 access

Ethernet CU

Figure 14-1 SMDS Internetworking Scenario

data units SMDS are capable of containing up to 9188 octets bytes of user information SMDS is

therefore capable of encapsulating entire IEEE 802.3 IEEE 802.4 IEEE 802.5 and FDDI frames

The size is large packet consistent with the high-performance objectives of the service

Addressing

Like other datagram protocols SMDS data units carry both source and destination address The

recipient of data unit can use the source address to return data to the sender and for functions such address as resolution discovering the mapping between higher-layer addresses and SMDS SMDS addresses addresses are 10-digit addresses that resemble conventional phone numbers

In addition SMDS supports group addresses that allow single data unit to be sent and then delivered the by network to multiple recipients Group addressing is analogous to multicasting on local-area networks LANs and is valuable feature in internetworking applications where it is

used for address and widely routing resolution dynamic discovery of network resources such as file servers

SMDS offers several other addressing features Source addresses are validated by the network to

that the ensure address in question is legitimately assigned to the SNI from which it originated Thus

users are protected against address spoofing that is sender pretending to be another user Source and destination address screening is also possible Source address screening acts on addresses as

data units are leaving the network while destination address screening acts on addresses as data

units are entering the network If the address is disallowed the data unit is not delivered With

14-2 Internetworking Technology Overview Access Classes

address screening subscriber can establish private virtual network that excludes unwanted traffic This provides the subscriber with an initial security screen and promotes efficiency because devices

attached to SMDS do not have to waste resources handling unwanted traffic

Access CHasses

To accommodate of traffic range requirements and equipment capabilities SMDS supports

variety of access classes Different access classes determine the various maximum sustained

information transfer well rates as as the degree of burstiness allowed when sending packets into the SMDS network

On DS-3-rate interfaces access classes are implemented through credit management algorithms

which track credit balances for each customer interface Credit is allocated on periodic basis up maximum the to some Then credit balance is decremented as packets are sent to the network

The of operation the credit management.scheme essentially constrains the customers equipment to sustained some or average rate of data transfer This average rate of transfer is less than the full

information carrying bandwidth of the DS-3 access facility Five access classes corresponding to

sustained information rates of 10 1625 and 34Mbps are supported for DS-3 access interface

The credit management scheme is not applied to DS-1-rate access interfaces

SMDS nterface ProtocoH SP

Access to the network is via is SMDS accomplished SIP The SIP based on the DQDB protocol

specified by the IEEE 802.6 MAN standard The DQDB protocol defines Media Access Control

that allows MAC protocol many systems to interconnect via two unidirectional logical buses

As designed by IEEE 802.6 the DQDB standard can be used to construct private fiberbased MANs

supporting variety of applications including data voice and video This protocol was chosen as

the basis for SIP because it was an open standard could support all the SMDS service features was designed for compatibility with carrier transmission standards and is aligned with emerging

standards for Broadband ISDN BISDN As BISDN technology matures and is deployed the

carriers intend to support not only SMDS but broadband video and voice services as well

To interface to SMDS networks only the connectionless data portion of the IEEE 802.6 protocol is needed SIP does Therefore not define voice or video application support

When used to gain access to an SMDS network operation of the DQDB protocol across the SNI

results in an access DQDB The term access DQDB distinguishes operation of DQDB across the SNI

from operation of DQDB in any other environment such as inside the SMDS network switch in

the network SMDS operates as one station on an access DQDB while customer equipment operates as one or more stations on the access DQDB

Because the DQDB protocol was designed to support variety of data and nondata applications and

because it is shared medium access control protocol it is relatively complex It has two parts

The protocol syntax

The distributed queuing algorithm that constitutes the shared medium access control

Switched Multimegabit Data Service 14-3 SMDS Interface Protocol SIP

CPE Configurations

There are two possible configurations of CPE on the SMDS access DQDB see Figure 14-2 In

single-CPE configuration the access DQDB simply connects the switch in the carrier network and one subscriber-owned station CPE In multi-CPE configuration the access DQDB consists of the

switch in the network and multiple interconnected CPE at the subscriber site In this latter

configuration all CPE must belong to the same subscriber

Single CPE

BusA

Bus

Figure 14-2 Single-CPE and Multi-CPE Configurations

In the single-CPE case the access DQDB is essentially just two-node DQDB subnetwork Each of nodes the the switch and the CPE transfer data to the other via unidirectional logical bus There

is no contention for this bus since there are no other stations Because of this the distributed

queueing algorithm need not be used Without the complexity of the distributed queuing algorithm

SIP for single-CPE configurations is much simpler than SIP for multi-CPE configurations

SP Leves

The SIP can be logically partitioned into three levels as shown in Figure 14-3

14-4 Internetworking Technology Overview SMDS Interface Protocol SIP

SMDS SDU

SIP level PDU HDR TRLR /N

SIP level PDU HDR TRLR HDR TRLR1 HDR TRLR1

HDR Header

PDU Protocol data unit

SDU Service data unit

TRLR Trailer

Figure 14-3 Encapsulation of User Information by SIP Levels

LeveI3

SIP level involves the operation encapsulation of SMDS service data units SDUs in level

header and trailer Level protocol data units PDUs are then broken into level PDUs as

appropriate to conform to level specifications

The SIP level PDU is reasonably complex It is shown in Figure 14-4

Number of octets Field length

in bytes bits bits 12 9188 04

lnfo1 RSVD BAsize DA HEL BEtag SA HE CRC Lenh HI Pad RSVDBEtag

BEtag Beginning-end tag BAsize Buffer allocation size

CRC Cyclic redundancy check DA Destination address

HE Header extension

HEL Header extension length

HLPI Higher-layer protocol identifier

lnfoPad Information padding to ensure that this field ends on 32-bit boundary SA Source address RSVD Reserved Carried across network unchanged

Figure 14-4 SIP Level PDU

Fields marked in the figure are not used in the provision of SMDSbut are present in the protocol

to ensure alignment of the SIP format with the DQDB protocol format Values placed in these fields by the CPE must be delivered unchanged by the network

Switched Multimegabit Data Service 14-5 SMDS Interface Protocol SIP

The two reserved fields must be populated with zeros The two BEtag fields contain an identical

value and are used to form an association between the first and last segments or level PDUs of

SIP level PDU These fields can be used to detect the condition where the last segment of one level

PDU and the first segment of the next level PDU are both lost resulting in receipt of an invalid level PDU

The BAsize field contains the buffer allocation size

and The destination and source addresses consist of two parts an address type an address In both

cases the address type occupies the four most significant bits of the field If the address is

destination address the address type may be either 1100 or 1110 The former indicates 60-bit

individual address the latter indicates 60-bit group address Tithe address is source address the

address type field can only indicate an individual address

Bellcore Technical Advisories specify how addresses consistent in format with the North American

Numbering Plan NANP are to be encoded in the source and destination address fields In this case

the four most significant bits of each of the source and destination address subfields contain the value

0001 which is the internationally defined country code for North America The next 40 bits

contains the binary coded decimal BCDencoded values of the 10-digit SMDS NANP-aligned

addresses The final 16 least-significant bits are populated with ones for padding

The higher-layer protocol identifier field indicates what type of protocol is encapsulated in the

information field This value is important to systems using the SMDS network such as Cisco

routers but is not processed or changed by the SMDS network

The header extension length HEL field indicates the number of 32-bit words in the header

extension field Currently the size of this field for SMDS is fixed at 12 bytes Therefore the HEL

value is always 0011

The header extension HE held is currently identified as having two uses One is to contain an

SMDS version number which is used to determine what version of the protocol is being used The

other use is to convey carrier selection value providing the ability to select particular

carrier interexchange to carry SMDS traffic from one local carrier network to another In the future other information may be defined to be conveyed in the header extension field if required

The CRC field contains cyclic redundancy check value

LeveI2

Level PDUs are segmented into uniformly sized 53-octet level PDUs often referred to as slots

or cells The format of the SIP level PDU is shown in Figure 14-5

Field length

in bits 32 14 352 10

Header Trailer

Figure 14-5 SIP Level PDU

14-6 Internetworking Technology Overview SMDS Interface Protocol SIP

The access control field of the SIP level PDU contains different values depending on the direction

of information flow If the slot is sent from the switch to the CPE only the indication of whether the

PDU contains information or not is important If the slot was sent from the CPE to the switch and

if the is configuration multi-CPE this field can also carry request bits that indicate bids for slots on

the bus from the switch going to the CPE Further detail on how these request bits are used to

implement distributed queuing media access control can be obtained from the IEEE 802.6 standard

The network control information field can contain only two possible values One particular bit

pattern is included when the PDU contains information another is used when it does not

The field segment type indicates whether this level PDU is the beginning slot the last slot or slot from the middle of level PDU Segment type values are shown in Table 14-1

Table 14-1 Segment Type Values

Value Meaning

00 Continuation of message

01 End of message

10 Beginning of message

11 Single segment message

The ID field allows association of level message PDUs with level PDU The message ID is the same for all segments of given level PDU On multi-CPE access DQDB level PDUs

originating from different CPE must have different message IDs This allows the SMDS network

receiving interleaved slots from different level PDUs to associate each level PDU with the

correct level PDU Successive level PDUs from the same CPE may have identical message IDs This since presents no ambiguity any single CPE must send all level PDUs from one level PDU

before it begins sending level PDUs of different level PDU

The segmentation unit field is the data portion of the PDU In the event of an empty level PDU

this field is populated with zeros

The field payload length indicates how many bytes of level PDU are actually contained in the

unit field segmentation If the level PDU is empty this field is also populated with zeros

the field contains 10-bit check value used Finally payload CRC cyclic redundancy CRC to detect the errors over segment type message ID segmentation unit payload length and payload CRC

fields This CRC does not cover the access-control or network-control information fields

Level

SIP level the provides physical link protocol which operates at DS-3 or DS-1 rates between the

CPE and the network SIP level is divided into two parts the transmission system sublayer and the

Physical Layer Convergence Protocol PLCP The transmission system sublayer defines the

characteristics and method of attachment to the transmission link that is the DS-3 or DS-1 The

PLCP how the level specifies PDUs or slots are to be arranged relative to the DS-3 or DS-1 frame and defines certain management information

the is Because SIP based on IEEE 802.6 it has the advantage of compatibility with future BISDN

interfaces that will support not only data but video and voice applications as well However this

compatibility does cost some protocol overheadwhich must be taken into account when calculating

overall data throughput that can be achieved using SIP Over DS-3 access DQDB the total

bandwidth available for level PDU user data is approximately 34 Mbps Over DS- access

approximately 1.2 Mbps can carry user data

Switched Multimegabit Data Service 14-7 SMDS Interface Protocol SIP

The use of the IEEE 802.6 MAN MAC protocol as the basis for the SMDS SIP means that local communication between CPE on the same access DQDB is possible Some of this local communication will be visible to the switch serving the SNI and some will not The switch therefore must use the destination address of data unit to differentiate between data units intended for

SMDS-based transfer and data units intended for local transmission among multiple CPE sharing an access DQDB

Network mpementaton

Inside the carrier network the high-speed packet-switching capability required by SMDS can be number of provided by different technologies In the near term switches based on MAN such the technology as DQDB standard are being included in number of networks series of Technical Advisories Beilcore produced by specify standard requirements on network equipment for such functions as the following

Network operations

Usage measurement for billing

Interface between local carrier network and long-distance carrier network

Interface between two switches inside the same carriers network

Customer network management

As has been noted the IEEE 802.6 and SIP protocol were intentionally designed to align with the BISDN referred principal protocol to as Asynchronous Transfer Mode ATM ATM and IEEE 802.6 belong to class of often referred to protocols as fast packet-switching or cell relay protocols These information protocols organize into small fixed-size cells level PDUs in SIP terminology Fixed-

size cells can be and switched in hardware processed at very high speeds This tightly constrains

delay characteristics cell useful making relay protocols for video and voice applications As ATM based switching equipment becomes available this technology will also be introduced into networks providing SMDS

14-8 Internetworking Technology Overview CHAPTER 15

Asynchronous Transfer Mode

Background

The foundational elements of Asynchronous Transfer Mode ATM were first synthesized by

researchers at ATT Bell Laboratories and France Telecoms Research Center in the early to mid

980s These researchers were interested in packetizing voice information so that one switching

fabric could be used for both data and voice Researchers believed that device capable of

packetizing and switching voice information would have to move at least one million packets per

second with millisecond-range queuing delays Because no existing packet-switching technology

was capable of these speeds the researchers were forced to consider new paradigms

researchers realized that scale Early ATM incorporating very large integration VLSI technology

into fabric enabled switches examine the of header and switching to and process contents packet

provide memory for buffering In particular the switch could quickly direct information through the

network after analyzing simple addresses contained in packet headers The researchers concluded

that networks of these switches could with minimal conceivably achieve very high performance delay

Another concept that was critical to the development of ATM was switching technique called fast

in that packet switching Fast packet switches differ from X.25-like packet-switching systems they

minimize storing processing and forwarding activity at each link For example error control and

flow control are performed on an end-to-end rather than on link-by-link basis By reducing the

activities at each link additional throughput is possible

As initially designed fast packet-switching systems handled variable-length packets The final

technical contribution toATMs development was the modification of fast packet switching to handle

small fixed-length packets called cells Short cells reduce queuing delay and increase the ability of

system elements to operate in parallel Fixed-size cells limit delay variance and ease buffer

allocation Limited delay variance is particularly important for supporting real-time traffic such as voice or video conversations

For wide-area networking ATM is currently being standardized for use in Broadband Integrated

Services Digital Networks BISDNs by the Consultative Committee for International Telegraph and Telephone CCITT and the American National Standards Institute ANSI Officially the ATM

layer of the BISDN model is defined by CCITT 1.36 one of many BISDN specifications

Although ATM was designed with wide-area networks WANs in mind many experts believe that another widespread use of ATM will be in campus network applications Local-area network LAN

managers need high throughput and improved scalability for network-intensive distributed

applications Large end users with low-delay high-bandwidth applications are seeking new network

technologies that can quickly move variety of source material for example data voice image and video between remote locations ATM has many of the characteristics these users want

Asynchronous Transfer Mode 15-1 Technology Basics

To promote ATM interoperability based on standards Cisco Systems and three other companies

NET/ADAPTIVE Northern Telecom and Sprint founded the ATM Forum in the fall of 1991 This

organization which now has over 300 members helps ensure ATM implementation compatibility

through various activities including publication of the ATM User-Network Interface Specfi cation

Tech noogy Basics

ATM is cell-switching and multiplexing technology that combines the benefits of circuit switching

constant transmission delay guaranteed capacity with those of packet switching flexibility

efficiency for intermittent traffic Like .25 and Frame Relay ATM defines the interface between

the user equipment and the network referred to as the User-Network Interface or UNJ This

definition supports the use of ATM switches and ATM switching techniques within both public and

private networks

Because it is an asynchronous mechanism ATM differs from synchronous transfer mode STM methods where time-division multiplexing TDM techniques are employed to preassign users to

time slots ATM time slots are made available on demand with labels identifying the source of the

transmission contained in each ATM cell TDM is inefficient relative to ATM because if station

has to transmit when its nothing time slot comes up that time slot is wasted The converse situation where station has lots one of information to transmit is also less efficient In this case that station

transmit when its can only turn comes up even though all the other time slots are empty With ATM station send labeled can cells whenever necessary Figure 15-1 contrasts TDM and ATM

multiplexing techniques

1DM Time slots

11/21/3 j/1 12/3/4/1 12/3/4/1 /21/3L4/1 IJ

Station data

fl Nothing to send

With TDM station can send only during preassigned time slot

ATM Cells

//p////PvIYP//1

Station data

Nothing to send

With station send labeled ATM can cells whenever necessary

15-1 Figure TDM and ATM Multiplexing Techniques

Another critical ATM design characteristic is its star topology The ATM switch acts as hub in the

with all ATM network devices attached directly This provides all the traditional benefits of star-

topology networks including easier troubleshooting and support for network configuration changes and additions

15-2 Internetworking Technology Overview Technology Basics

fabric Furthermore ATMs switching provides additive bandwidth As long as the switch can handle

the cell transfer additional aggregate rate connections to the switch can be made The total

bandwidth of the increases If switch cells system accordingly can pass among all its interfaces at the full rate of all interfaces it is described as nonbiocking For example an ATM switch with 16 ports each at 155 megabits second would about per Mbps require 2.5 gigabits per second Gbps aggregate throughput to be nonbiocking

consists of three functional ATM layersthe ATM physical layer the ATM layer and the ATM

adaptation to layerthat correspond roughly layer and parts of layer such as error control and data framing of the Open System Interconnection OSI reference model

The first layer is the ATM The physical layer ATM physical layer controls transmission and receipt

of bits on the medium It also track physical keeps of ATM cell boundaries and packages cells into

the of frame for the medium appropriate type physical being used Above the physical layer is the

ATM layer which is for responsible establishing virtual connections and passing ATM cells through the ATM network above the Immediately ATM layer is the ATM adaptation layer The ATM

translates between the adaptation layer larger service data units SDUs for example video streams and data of packets upper-layer processes and ATM cells Several ATM adaptation layers are and currently specified they are analyzed later in this chapter Finally aboe the ATM adaptation are layer higher-layer protocols representing traditional transports and applications

ATM Physica Layer

The ATM is divided into physical layer two parts the physical medium sublayer and the transmission convergence sublayer The physical medium sublayer is responsible for sending and

continuous flow of bits with receiving associated timing information to synchronize transmission

and Because it includes reception only physical-medium-dependent functions its specification depends on the physical medium used

can use medium ATM any physical capable of carrying ATM cells Some existing standards that can cells SONET carry ATM are Synchronous Optical Network/SDH DS-3/E3 100-Mbps local fiber

physical and local fiber Channel FDDI layer 55-Mbps Fiber physical layer Various proposals for use over twisted pair are also under consideration

The transmission convergence sublayer is responsible for the following

Cell delineationMaintains ATM cell boundaries

Header control error sequence generation and verificationGenerates and checks header

error control code to ensure valid data

Cell rate decouplingInserts or suppresses idle unassigned ATM cells to adapt the rate of valid ATM cells to the payload capacity of the transmission system

Transmission frame adaptationPackages ATM cells into frames acceptable to the particular

physical-layer implementation

Transmission frame generation and recoveryGenerates and maintains the appropriate

physical-layer frame structure

ATM Layer

The is ATM layer responsible for establishing connections and passing cells through the ATM network To do this it uses the information contained in the ATM cells Each ATM cell consists of

48 octets of payload and five octets of header information The five header octets contain

information the the identifying path through network as well as congestion indicators the payload

type and other parameters The payload portion carries upper-layer information

Asynchronous Transfer Mode 15-3 Technology asics

An ATM cell is shown in Figure 15-2 The header begins with bits of generic flow control GFC

information This field can be used to provide standardized local functions such as media access

control when multiple stations share single switch port Values within this field are not carried end

to end and are overwritten by the ATM network

Field length 48

in octects

Field length in bits 16 31

GFC Generic flow control

VPI Virtual path identifier

Vol Virtual channel identifier

PT Payload type Call loss CLP priority HEC Header error control

Figure 15-2 ATM Cell

Following the GFC field the ATM specification calls for bits of virtual path identUler VPI

information and 16 bits of virtual channel identifier VCI information These two fields are commonly referred to as one called the VPI/VCI field or value

Together the VPI and VCI provide ATM with two connection concepts virtual channel is simply

the classical notion of the virtual circuit providing logical connection between two users virtual

path defines bundle of virtual channels along some segment of their route through the network Many virtual channels can use the same virtual path

Using two-part connection identifier helps speed operations at each link Once virtual path is

established adding another virtual channel to that path involves very little overhead In addition

number of data transport functions such as traffic management can be performed at the virtual path

level simplifying the network architecture

ATM virtual connections are formed by linking VPIIVCI values on different ports as illustrated in

Figure 15-3 When cell with VPJJVCI 29 arrives at port of the ATM switch the switch looks in

its table and learns that it must translate the VPIIVCI value to 45 and output the cell on port

Similarly cell with VPIIVCI 64 arriving at port will be output on port with VPIJVCh29

Transit in the opposite directions over the same circuits results in full-duplex operations As this

example illustrates VPIIVCI values are unique only on single interface not throughout the ATM network

15-4 Internetworking Technology Overview ATM Adaptation Layers

Port

Port VPINCI Port VPINCI

______29J

Figure 15-3 Virtual Connections Through an ATM Switch

Following the VPI/VCI information is the 3-bit payload type PT field The first bit indicates user

data or control data if the first bit indicates user data the middle bit indicates congestion and the

last bit indicates the end of the frame

The next field is the 1-bit cell loss priority CLP field This field allows the user or network to

optionally indicate the explicit loss priority of the cell value of one means that the cell may be

discarded first if necessary value of zero means that the cell should not be discarded as readily

Discarding cells with both CLP values might be necessary when severe network congestion is

present

Finally the 8-bit header error control HEC field is used to detect multiple-bit errors and optionally

correct single-bit errors in the header It can also be used for cell delineation by searching the bit

stream for repeating pattern of valid HEC values

ATM Adaptation Layers

ATM adaptation layers AALs segment upper-layer information into cells at the transmitter and

reassemble them at the receiver Several AAL specifications exist including AAL1 and AAL2

which support voice video and similar traffic and AAL3/4 and AAL5 which support data communications

ATM AALs are used to support four service classes which are shown in Table 15-1 Class will

probably be used to transport the existing telephone digital hierarchy Class is similar to class

except that in class the bit rate is variable so it is more appropriate for compressed video where

the information rate changes with scene content Classes and will be used to transport data in

connection-oriented and connectionless environments respectively

Asynchronous Transler Mode 15-5 ATM Adaptation Layers

Table 15-1 BISDN Service Classes

Class Class Class Class Characteristic AAL1 AAL2 AAI 3/4 or AAL5 AAI3/4 or AAL5

Not Timing relationship Required Required Not required required

between source and

destination

Bit rate Constant Variable Variable Variable

Connection mode Connection- Connection- Connection- Connectionless

oriented oriented oriented

data AAL3/4 and AAL5 can each carry both connection-oriented and connectionless packets They

and is in its are essentially two different ways of doing the same thing Work on AAL AAL2 early

stages

AAL314

AAL3/4 is divided into two sublayers convergence sublayer CS and segmentation and

reassembly sublayer SAR The CS itself has two parts common part convergence sublayer

and The is not standardized CPCS service-specific convergence sublayer SSCS SSCS yet fully

The CPCS is designed primarily for error control

Figure 15-4 shows how AAL3/4 treats payload frame The CPCS encapsulates information within

4-octet header and 4-octet trailer Once encapsulated the CS protocol data unit PDU is broken

into 44-octet units with 2-octet header and 2-octet trailer inside the cell payload by the SAR

sublayer In the SAR header are two bits that indicate whether the cell is the beginning of message

continuation of message or end of message Single segment messages that begin and end in one cell are also possible message ident/ler MID in the SAR header allows multiple messages to

interleave on single virtual connection

Data frame

AAL3/4

convergence

sublayer

Adaptation AAL3/4

layer segmentation and

reassembly

sublayer

ATM layer

Figure 15-4 AAL3/4 Treatment of Payload Frame

15-6 Internetworking Technology Overview ATM Adaptation Layers

Finally the SAR PDU is inserted into the 48-octet payload of the ATM cell at the ATM layer The

distinguishing features of this are ten-bit cell technology CRC per rather than per frame and the fact that it is to frames possible multiplex onto single virtual connection Figure 15-5 shows AAL3/4 SAR state simplified diagram which tracks the progress of packet on single VPIIVCI and MID

Beginning of message

Continuation of message

fmessage

Single segment message

Figure 15-5 AAL3/4 SAR Sublayer State Diagram

AAL5

Packet delimiting in AAL5 is performed within the ATM cell header rather than within the SAR

PDU header as inAAL3/4 Also error detection is provided by length field and 32-bit-per-frame CRC rather than 10-bit by per-cell CRC as in AAL34 Payload frame treatment by AAL5 is shown in Figure 15-6

Data frame

Convergence

sublayer

AAL5

SAR

sublayer

ATM layer

I-

Figure 15-6 AAL5 Treatment of Payload Frame

Asynchronous Transfer Mode 15-7 ATM Architectures

trailer the frame The The AAL5 convergence sublayer appends pad and an 8-octet to payload pad

ensures that the AAL5 PDU falls exactly on 48-octet cell payload boundary The AAL5 and 32-bit convergence sublayer trailer includes the length of the data frame CRC computed across the data receiver the entire payload By checking that the length and CRC still match frame can

detect bit errors and lost or misordered cells

into 48-octet After processing by the convergence sublayer the AAL5 PDU is then segmented

blocks without the additional SAR header or trailer required by AAL3/4 Messages are not

Then data cells with interleaved instead empty cells are sent until the data frame is ready are sent

cell is with the the end-of-message EOM bit in the header set to zero and the last data sent BOM 15-7 these blocks bit set to one simplified illustration of this process is shown in Figure Finally

are placed directly into the ATM cell payload field OMOEOMO

Empty cell

Figure 15-7 AAL5 Convergence Sublayer State Diagram

AAL5 is gathering momentum because several computer vendors including Sun Microsystems

plan to support it in their products The applications on such computers will help drive the success

of ATM in data networks

Connecting computers that use different AALs is somewhat analogous to connecting computers on

different shared-media LANs foi example Ethernet and Token Ring router/bridge or other

internetworking device must convert between the two frame and cell types

ATM Architectures

As simplified in standards documents the ATM architecture consists of super terminals very fast

intelligent terminals with large graphics displays and multimedia capability that connect directly to

public ATM networks Unfortunately this model ignores the current heterogeneous installed base

and the economic necessity of at least some private networking

more practical ATM architecture calls for connectivity with todays wide variety of installed

networks through internetworking devices such as routers to an ATM network as shown in

Figure 15-8 The ATM network could consist of both public and private portions

15-8 Internetworking Technology Overview ATM Architectures

File server

switch

Ethernet

IBM mainframe with

front-end processor

Figure 15-8 Practical ATM Architecture

Network planners for data choose from considering ATM can among three ATM implementation TM techniques permanent-virtual-connection PVC service ATM switched-virtual-connection and ATM SVC service connectionless service In the following sections the term router is used to

refer to any ATM end point

ATM Permaieiit Virtual Ctnmection PVC Service

ATM PVC shown in service Figure 15-9 operates much like Frame Relaya virtual connection

mesh partial mesh or star is administratively established through the ATM network between the

routers ATM PVC service was the original focus of the ATMForum

Asynchronous Transfer Mode 15-9 ATM Architectures

Figure 15-9 ATM PVC Service

Advantages of ATM PVC service include direct ATM connection between routers and the

simplicity of the specification and subsequent implementation Disadvantages include static

connectivity and the administrative overhead of provisioning virtual connections manually

ATM Switched Virtua Connection SVC Service

ATM SVC service shown in Figure 15-10 operates much like X.25 SVC service although ATM

allows much higher throughput Virtual connections are created and released dynamically providing

user bandwidth on demand This service requires signaling protocol between the router and the

network The ATM Forum is currently drafting signaling implementation agreement based on

continuing CCITT standardization

Router

Signaling

Figure 15-10 ATM SVC Service

Advantages of the ATM SVC service include good general connectivity and simple administration

Its disadvantages include immature standards and potentially slow SVC setup

15-10 Internetworking Technology Overview ATM Architectures

ATM Coirnectionless Service

ATM connectionless service shown in Figure 15-11 operates much like Switched Multimegabit

Data Service SMDS In this scheme virtual connection is administratively established between

the router and connectionless server Jinction CLSF an ancillary part of the ATM switch The CLSF forwards data frames based on the destination address which can be multicast address

included in each frame not each cell No signaling is required because all connections to the CLSF

are preestablished Many telecommunications carriers are introducing metropolitan area network MAN trials and services and plan to migrate toward ATM connectionless service

Figure 15-11 ATM Connectionless Service

The advantages of ATM connectionless service include good connectivity and strong match with

many of todays popular connectionless protocols The Internet communitys Internet Protocol IP and Novells Internet Packet Exchange IPX are examples of these protocols The primary

disadvantage of this approach is that the CLSF can become throughput bottleneck or single point

of failure

Asynchronous Transfer Mode 15-11 ATM Architectures

15-12 Internetworking Technology Overview

CHAPTER 16

AppleTalk

Background

In the early 980s as Apple Computer Inc was preparing to introduce the Macintosh Apple

engineers knew that networks would become critical need They wanted to ensure that

Macintosh-based network was seamless extension of the revolutionary Macintosh user interface

With these two in decided goals mind Apple to build network interface into every Macintosh and

to integrate that interface into the desktop environment Apples new network architecture was called AppleTalk

Although AppleTalk is proprietary network Apple has published AppleTalk specifications in an

to attempt encourage third-party development Today many companies are successfully marketing AppleTalk-based products including Novell Inc and Microsoft Corporation

The of original implementation AppleTalk which was designed for local workgroups is now

commonly referred to as AppleTalk Phase With the installation of over 1.5 million Macintosh

in the first five computers years of the products life however Apple found that some large

corporations were exceeding the built-in limits of AppleTalk Phase so they enhanced the protocol The enhanced known protocols as AppleTalk Phase enhanced AppleTalks routing capabilities and allowed AppleTalk to run successfully in larger networks

TechnoHogy Basics

AppleTalk was designed as client-server distributed network system In other words users share

network resources such as files and printers with other users Computers supplying these network called resources are servers computers using servers network resources are called clients Interaction with servers is essentially transparent to the user because the computer itself determines

the location of the requested material and accesses it without further information from the user In

addition their to ease of use distributed systems also enjoy an economic advantage over peer-to-peer systems because important materials can be located in few rather than many locations

AppleTalk corresponds relatively well to the OSI reference model In Figure 16-1 AppleTalk

are shown to the OSI This differs protocols adjacent layers to which they map figure from some

other depictions of how the AppleTalk protocol stack relates to the OSI model in that it places the

Name Binding Protocol NBP Zone Information Protocol ZIP and Routing Table Maintenance Protocol RTMP at layer and the AppleTalk Echo Protocol AEP at layer Cisco believes that

NBP ZIP and RTMP are more closely aligned functionally to layer of the OSI model even

though they use the services of the Datagram Delivery Protocol DDP another layer protocol

Similarly Cisco believes that AEP should be listed as an application-layer protocol because it is

commonly used to provide application-layer functionality Specifically AEP helps determine the

ability of remote nodes to receive incoming connections

AppleTalk 16-1 Media Access

Other protocols shown in Figure 16-1 are the AppleTalk Transaction Protocol ATPAppleTalk Data Stream Protocol ADSP and AppleTalk Address Resolution Protocol AARP

OS Reference

Model AppleTalk Protocols

Application

AppleTalk Data Zone Information AppleTalk Printer Access Protocol Session Stream Protocol Protocol Session Protocol ADSP ZIP ASP PAP

Routing Table Name Binding Transport Maintenance Ech Protocol Transaction pPleTalk APPleTalk Protocol NBP Protocol RTMP AEP Protocol ATP

Datagram Delivery Protocol DDP Network

Address Resolution Protocol AARP

EtherTalk Link LocalTalk Link TokenTalk Link FDDITaIk Data Link Access Protocol Access Protocol Access Protocol ELAP LLAP TLAP FLAP

Ethernet LocalTalk TokenTalk FDDI Physical Hardware Hardware Hardware Hardware

Figure 16-1 AppleTalk and the OSI Reference Model

Meda Access

Apple constructed AppleTalk to be link-layer independent In other words it can theoretically run

on top of any link-layer implementation Apple supports variety of link-layer implementations including Ethernet Token Ring Fiber Distributed Data Interface FDDI and LocalTalk Apple

refers to AppleTalk over Ethernet as EtherTalk to AppleTalk over Token Ring as TokenTalk and to

AppleTalk over FDDI as FDDITa1k For more information on Ethernet Token Ring and FDDI

technical characteristics see Chapter Ethernet/IEEE 802.3 Chapter Token Ring/IEEE

802.5 and Chapter Fiber Distributed Data Interface respectively

LocalTalk is Apples proprietary media-access system It is based on contention access bus

topology and baseband signaling and runs on shielded twisted-pair media at 230.4 kbps The

physical interface is RS-422 balanced electrical interface supported by RS-449 LocalTalk nodes segments can span up to 300 meters and support maximum of 32

16-2 Internetworking Technology Overview Network Layer

Network Layer

This section describes AppleTalk network-layer concepts and protocols It includes discussion of

protocol address assignment network entities and AppleTalk protocols that provide OSI reference

model layer functionality

Protoco Address Assignment

To ensure minimal network administrator overhead AppleTalk node addresses are assigned

dynamically When Macintosh running AppleTalk starts up its chooses protocol network-layer

address and checks to see whether that address is currently in use If not the new node has

successfully assigned itself an address If the address is currently in use the node with the conflicting

address sends message indicating problem and the new node chooses another address and

repeats the process Figure 16-2 shows the AppleTalk address selection process

Id like

addre37 address 37

o0 00

Macintosh Macintosh

Macintosh

Figure 16-2 AppleTalk Address Selection Process

AppleTalk 16-3 Network Layer

The actual mechanics of AppleTalk address selection are media dependent The AppleTalk Address

Resolution Protocol is used to associate addresses with AARP AppleTalk particular media

addresses also AARP associates other protocol addresses with hardware addresses When either

AppleTalk or any other protocol stack must send packet to another network node the protocol

address is passed to AARP AARP first checks an address cache to see whether the relationship between the protocol and the hardware address is already known If so that relationship is passed

up to the inquiring protocol stack If notAARP initiates broadcast or multicast message inquiring

about the hardware address for the protocol address in question If the broadcast reaches node with

the specified protocol address that node replies with its hardware address This information is

passed up to the inquiring protocol stack which uses the hardware address in communications with

that node

Network Entites

identifies several network AppleTalk entities The most elemental is node which is simply any

device connected to an AppleTalk network The most common nodes are Macintosh computers and

laser but other printers many types of computers are also capable of AppleTalk communication IBM including PCs Digital Equipment Corporation VAX computers and variety of workstations The next defined entity by AppleTalk is the network An AppleTalk network is simply single cable the logical Although logical cable is frequently single physical cable some sites use bridges

to interconnect several physical cables Finally an AppleTalk zone is logical group of possibly

noncontiguous networks These AppleTalk entities are shown in Figure 16-3

16-4 Internetworking Technology Overview Network Layer

Zone

Figure 16-3 AppleTalk Entities

Datagram Delivery Protoco DDP

AppleTalks primary network-layer protocol is the Datagram Delivery Protocol DDP DDP

provides connectionless service between network sockets Sockets can be assigned either statically

or dynamically

AppleTalk addresses which are administered by the DDP consist of two components 16-bit

network number and an 8-bit node number The two components are usually written as decimal

numbers separated by period for example 10.1 means network 10 node .When an 8-bit socket

is network number and node identifying particular process added to the number unique process

on network is specified

AppleTalk Phase distinguishes between nonextended and extended networks In nonextended

network such as LocalTalk each AppleTalk node number is unique Nonextended networks were the

extended network such as EtherTalk and sole network type defined in AppleTalk Phase In an TokenTalk each network number/node number combination is unique

the router Each Zones are defined by the AppleTalk network manager during configuration process Extended networks can have node in an AppleTalk network belongs to single specific zone

networks to zone multiple zones associated with them Nodes on extended can belong any single associated with the extended network

AppleTalk 16-5 Network Layer

Routing Tabe Maintenance Protoco RTMP

The protocol that establishes and maintains AppleTalk routing tables is called the Routing Table

Maintenance Protocol RTMP RTMP routing tables contain an entry for each network that

datagram can reach Each entry includes the router port that leads to the destination network the

node ID of the next router to receive the packet the distance in hops to the destination network and

the current state of the entry good suspect or bad Periodic exchange of routing tables allows the

routers in an internet to ensure that they supply current and consistent information Figure 16-4

shows sample RTMP table and the corresponding network architecture

er1Routing Table

Network Distance Port Next router Entry state

Good

Router Good

Figure 16-4 Sample AppleTalk Routing Table

AppleTalks Name Binding Protocol NBP associates AppleTalk names expressed as network-

visible entities or NVEs with addresses An NVE is an AppleTalk network-addressable service

such as socket NVEs are associated with one or more entity names and attribute lists Entity names character such are strings as printer@ net while attribute lists specify NVE characteristics

Named associated NVEs are with network addresses through the process of name binding Name be done when the binding can user node is first started up or dynamically immediately before first orchestrates the use NBP name binding process which includes name registration name

confirmation name deletion and name iookup

Zones allow in name lookup group of logically related nodes To look up names within zone an

NBP lookup request is sent to local router which sends broadcast request to all networks that have nodes belonging to the target zone The Zone Information Protocol ZIP coordinates this effort

16-6 Internetworking Technology Overview Transport Layer

ZIP maintains network number to zone name mappings in zone information tables ZITs ZITs are

stored in routers which are the primary users of ZIP but end nodes use ZIP during the startup

process to choose their zone and to acquire internetwork zone information ZIP uses RTMP routing

tables to keep up with network topology changes When ZIP finds routing table entry that is not in

the ZIT it creates new ZIT entry Figure 16-5 shows sample ZIT

Network number Zone

Your

Marketing

Documentation

5-5 Sales

Figure 16-5 Sample AppleTalk ZIT

Transport Layer

AppleTalks transport layer is implemented by two primary Apple protocolsAppleTalk Transaction

Protocol ATP and AppleTalk Data Stream Protocol ADSP ATP is transaction oriented while

ADSP is data-stream oriented

AppeTak Transactoti Protoco AlP

ATP is one of AppleTalks transport-layer protocols ATP is suitable for transaction-based

applications such as those found in banks or retail stores

ATP transactions consist of requests from clients and replies from servers Each request/reply

pair has particular transaction ID Transactions occur between two socket clients ATP uses exactly once XO and at-least-once ALO transactions XO transactions are required in those situations

where accidentally performing the transaction more than once is unacceptable Bank transactions are

examples of such nonidempotent situationssituations where repeating transaction causes problems by invalidating the data involved in the transaction

ATP is capable of most important transport-layer functions including data acknowledgment and

retransmission packet sequencing and fragmentation and reassembly ATP limits message

segmentation to packets and ATP packets cannot contain more than 578 data bytes

AppDeTak Data Stream Protoco ADSP

ADSP is another important AppleTalk transport-layer protocol As its name implies ADSP is data-

stream rather than transaction oriented It establishes and maintains full-duplex data streams

between two sockets in an AppleTalk internetwork

AppleTalk 16-7 Upper-Layer Protocols

ADSP is reliable protocol in that it guarantees that data bytes will be delivered in the same order

as they were sent and that they are not duplicated ADSP numbers each data byte to keep track of

the individual elements of the data stream

ADSP also specifies flow-control mechanism The destination can essentially slow source

transmissions by reducing the size of its advertised receive window

ADSP also provides an out-of-band control message mechanism Attention packets are used as the vehicle for movement of out-of-band control messages between two AppleTalk entities These

number differentiate them from normal packets use separate sequence stream to ADSP data packets

UpperLayer ProtocoDs

AppleTalk supports several upper-layer protocols The AppleTalk Session Protocol ASP

establishes and maintains sessions logical conversations between an AppleTalk client and server

AppleTalks Printer Access Protocol PAP is connection-oriented protocol that establishes and maintains connections between clients and servers Use of the term printer in this protocols title is

purely historical The AppleTalk Echo Protocol AEP is an extremely simple protocol that

generates packets that can be used to test the reachability of various network nodes Finally the

AppleTalk Filing Protocol AFP helps clients share server files across network

16-8 Internetworking Technology Overview CHAPTER 17

DECnet

Background

Digital Equipment Corporation Digital developed the DECnet protocol family to provide well-

its The version of thought-out way for computers to communicate with one another first DECnet

released in 1975 allowed two directly attached PDP- 11 minicomputers to communicate In more remains recent years Digital has included support for nonproprietary protocols but DECnet the most

important of Digitals network product offerings

DECnet is currently in its fifth major product release sometimes called Phase and referred to as

DECnet/OSI in Digital literature DECnet Phase is superset of the OSI protocol suite and

supports all OSI protocols as well as several other proprietary and standard protocols that were

supported in previous versions of DECnet As with past changes to the protocol DECnet Phase is

compatible with the previous release Phase IV in this case

DgitaH Network Architecture DNA

Contrary to popular belief DECnet is not network architecture at all but is rather series of

products conforming to Digitals Digital Network Architecture DNA Like most comprehensive

network architectures from large systems vendors DNA supports large set of both proprietary and

standard protocols The list of DNA-supported technologies grows constantly as Digital implements

new protocols Figure 17-1 illustrates an incomplete snapshot of DNA and the relationship of some

of its components to the OSI reference model

DECnet 17-1 Media Access

OSI reference model DNA

Application DNA applications OSI applications

Presentation OSI presentation DNA DNA

name session

service control Session OSI session

Transport NSP TPO TP2 TP4

ES-IS IS-IS

Network Connectionless Connection-oriented CLNP CLNS X.25 CMNP

Link

Various link-access protocols

Physical

Figure 17-1 DNA and the OSI Reference Model

Meda Access

As 17-1 Figure shows DNA supports variety of media and link implementations Among these are well-known standards such as Ethernet Token Ring Fiber Distributed Data Interface FDDIIEEE and X.25 See 8022 ChapterS Ethernet/IEEE 802.3 Chapter Token Ring/IEEE 802.5

Chapter Fiber Distributed Data Interface Chapter 11 Synchronous Data Link Control and and Derivatives Chapter 12 .25 for more information on these protocols DNA also offers

traditional point-to-point link-layer protocol called Digital Data Communications Message Protocol DDCMP and 70-Mbps bus used in the VAXciuster called the computer-room interconnect bus CI bus

Network Layer

DECnet both connectionless and connection-oriented network supports layers Both network layers are implemented by OSI protocols The connectionless implementation uses the Connectionless Network Protocol CLNP and the Connectionless Network Service CLNS The connection-

oriented network uses the X.25 Packet-Level Protocol is layer PLPwhich also known as X.25 level and the Connection-Mode Network Protocol CMNP These OSI protocols are described more completely in Chapter 20 OSI Protocols

Although most of DNA was brought into OSI conformance with DECnet Phase DECnet Phase

IV routing was similar to OSI Phase already very routing DNA routing consists of OSI routing and ES-IS IS-IS plus continued support for the DECnet Phase IV routing protocol ES-IS and IS IS are described in Chapter 28 OSI Routing

17-2 Internetworking Technology Overview Network Layer

DECnet Phase Routing Frame Format

The DECnet Phase IV routing protocol differs from IS-IS in several ways One difference is in the

protocol header The DNA Phase IV routing layer header is shown in Figure 17-2 Is-Is packet

formats are shown in Chapter 28 OSI Routing

Field length mbytes

Routing Destination Source Nodes node flags node traversed .i

Figure 11-2 DNA Phase IV Routing Layer Header

The first field in DNA Phase IV routing header is the routing flags field which includes

return-to-sender bit which if set indicates that the packet is returning to the source

return-to-sender-request bit which if set indicates that request packets should be returned to

the source if they cannot be delivered to the destination

An intraLAN bit which is on by default If the router detects that the two communicating end

systems are not on the same subnetwork it turns the bit off

Other bits that indicate header format whether padding is being used and other functions

The destination node and source node fields identify the network addresses of the destination nodes

and the source node

The nodes traversed field shows the number of nodes the packet has traversed on its way to the

destination This field allows implementation of maximum hop count so that obsolete packets can

be removed from the network

DECnet identifies two types of nodes end nodes and routing nodes Both end nodes and routing

nodes can send and receive network information but only routing nodes can provide routing services

for other DECnet nodes

DECnet routing decisions are based on cost an arbitrary measure assigned by network

administrators to be used in comparing various paths through an internetwork environment Costs

are typically based on hop count media bandwidth or other measures The lower the cost the better

the path When network faults occur the DECnet Phase IV routing protocol uses cost values to

recalculate the best paths to each destination Figure 17-3 illustrates the calculation of costs in

DECnet Phase IV routing environment

DECnet 17-3 Network Layer

Best path to destination

Source LII Destination

17-3 Figure DECnet Phase IV Routing Protocol Cost Calculation

Addressing

DECnet addresses are not associated with the physical networks to which the nodes are connected Instead DECnet locates hosts area/node address An areas value using pairs ranges from to 63 inclusive node address be can between and 1023 inclusive Therefore each area can have nodes and 1023 approximately 65000 nodes can be addressed in DECnet network Areas can span many routers and single cable can support many areas Therefore if node has several network

interfaces it uses the area/node same address for each interface Figure 17-4 shows sample DECnet

network with several addressable entities

10.1

Area Node number number

Area 10 Area5

Figure 17-4 DECnet Addresses

DECnet hosts do not use manufacturer-assigned Media Access Control MAClayer addresses Instead network-level addresses are embedded in the MAC-layer address according to an algorithm that the multiplies area number by 1024 and adds the node number to the The product resulting

17-4 Internetworking Technology Overview Network Layer

16-bit decimal address is converted to hexadecimal number and appended to the address

AAOO.0400 in with byte-swapped order the least significant byte first For example DECnet address 12.75 becomes 12363 which base 10 equals 304B base 16 After this byte-swapped address is

to the standard DECnet appended MAC address prefix the resulting address is AAOO .0400 .4B30

Roung LeveOs

DECnet routing nodes are referred to as either level or level routers level router communicates with end nodes and with other level routers in particular area Level routers

communicate with level routers in the same area and with level routers in different areas

level and level Together routers form hierarchical routing scheme This relationship is

illustrated in Figure 17-5

Level Level router routet End

system ______

Level router

Area 10

Level router

Level C0 router CU

Area

Figure 17-5 DECnet Level and Level Routers

End systems send routing requests to designated level router The level router with the highest

priority is elected to be the designated router If two routers have the same priority the one with the

larger node number becomes the designated router routers priority can be manually configured

to force it to become the designated router

DECnet 17-5 Transport Layer

As shown in Figure 17-5 multiple level routers can exist in any area When level router wishes

level in the In to send packet outside its area it forwards the packet to router same area some cases the level router may not have the optimal path to the destination but the mesh network

the of level configuration offers degree of fault tolerance not provided by simple assignment one

router per area

Transport Layer

both and standard The DNA transport layer is implemented by variety of transports proprietary

described in detail in OSI transports TPO TP2 and TP4 are supported These are greater Chapter 20 OSI Protocols

similar in that it offers Digitals own Network Services Protocol NSP is functionally to TP4 connection-oriented flow-controlled service with message fragmentation and reassembly Two

subchannels are supportedone for normal data and one for expedited data and flow control

information Two flow control types are supporteda simple start/stop mechanism where the

receiver tells the sender when to terminate and resume data transmission and more complex flow

control technique where the receiver tells the sender how many messages it can accept NSP can also

respond to congestion notifications from the network layer by reducing the number of outstanding

messages it will tolerate

UpperLayer Protocolls

its well Above the transport layer DECnet supports own proprietary upper-layer protocols as as

standard OSI upper-layer protocols DECnet application protocols use the DNA session control

protocol and the DNA name service OSI application protocols are supported by OSI presentation

and session-layer implementations See Chapter 20 OSI Protocols for more information on these

OSI protocols

1-6 Internetworking Technology Overview CHAPTER 18

Internet Protocols

Background

In the mid-i 970s the Defense Advanced Research Projects Agency DARPA became interested in

establishing packet-switched network to provide communications between research institutions in

the United States DARPA and other government organizations understood the potential of packet-

switched technology and were just beginning to face the problem virtually all companies with networks now have communication between dissimilar computer systems

With the goal of heterogeneous connectivity in mind DARPA funded research by Stanford

University and Bolt Beranek and Newman BBN to create series of communication protocols

The result of this development effort completed in the late 1970s was the Internet protocol suite of

which the Transmission Control Protocol TCP and the Internet Protocol IP are the two best known

The Internet be used communicate of interconnected networks protocols can to across any set They are equally well suited for local-area network LAN as well as wide-area network WAN communications The Internet suite includes and not only lower-layer specifications like TCP IP

but also specifications for such common applications as mail terminal emulation and file transfer

Figure 18-1 shows some of the more important Internet protocols and their relationship to the OSI

reference model

Internet Protocols 18-1 Network Layer

OSI reference model The Internet orotocol suite

Application NFS

FTP Telnet Presentation XDR SMTP SNMP

Session RPC

Transport TCP UDP

Routing protocols ICMP Network lP

ARP RARP

Link

Not specified

Physical

______

Figure 18-1 Internet Protocol Suite and the OSI Reference Model

Creation and documentation of the Internet protocols closely resembles an academic research

project The protocols are specified in documents called Requestfor Comments RFCs RFCs are

published and then reviewed and analyzed by the Internet community Protocol refinements are

published in new RFCs Taken together the RFCs provide colorful history of the people

companies and trends that shaped the development of what is today the worlds most popular open

system protocol suite

Network Layer

IP is the primary layer protocol in the Internet suite In addition to internetwork routing IP

provides fragmentation and reassembly of datagrams and error reporting Along with TCP IP

represents the heart of the Internet protocol suite The IP packet format is shown in Figure 18-2

18-2 Internetworking Technology Overview Network Layer

32 bits

Version IHL Type of service Total length

Identification Flags Fragment offset

Time to Protocol Header checksum

live

Source address

Destination address

Options padding

Data variable

Figure 18-2 IP Packet Format

used The IP header begins with version number which indicates the version of IP currently

32-bit words The IP header length IHL field indicates the datagram header length in

The type-of-service field specifies how particular upper-layer protocol would like the current

this field datagram to be handled Datagrams can be assigned various levels of importance through

The total length field specifies the length of the entire IF packet including data and header in bytes

The identification field contains an integer that identifies the current datagram This field is used to help piece together datagram fragments

low-order bits control One bit The flags field is three-bit field of which the two fragmentation

second bit whether the is the specifies whether the packet can be fragmented the specifies packet last fragment in series of fragmented packets

The time-to-live field maintains counter that gradually decrements down to zero at which point the datagram is discarded This keeps packets from looping endlessly

receives after IP The protocol field indicates which upper-layer protocol incoming packets processing is complete

The header checksum field helps ensure IF header integrity

The source and destination address fields specify the sending and receiving nodes

such The options field allows IP to support various options as security

The data field contains upper-layer information

Internet Protocols 18-3 Network Layer

Addresshig

As with all network-layer protocols IPs addressing scheme is integral to the process of routing IP

datagrams through an intemetwork An IP address is 32 bits in length divided into either two or

three parts The first part designates the network address the second part if present designates the

subnet address and the final part designates the host address Subnet addresses are only present if

the network administrator has decided that the network should be divided into subnetworks The

lengths of the network subnet and host fields are all variable

IP addressing supports five different network classes The leftmost bits indicate the network class

Class networks are intended mainly for use with few very large networks since they provide

only seven bits for the network address field

Class networks allocate 14 bits for the network address field and 16 bits for the host address

field This address class offers good compromise between network and host address space

Class networks allocate 22 bits for the network address field Class networks only provide

eight bits for the host field however so the number of hosts per network may be limiting factor

Class addresses are reserved for multicast groups as described formally in RFC 1112 In class

addresses the four highest-order bits are set to and

Class addresses are also defined by IPbut are reserved for future use In class addresses the

four highest-order bits are all set to

IP addresses are written in dotted decimal formatfor example 34.10.2.1 Figure 18-3 shows the

address formats for class and IP networks

Class

Network Host

Class

Network Host

Class iLi

Host Network

Figure 18-3 Class and Address Formats

IP networks can also be divided into smaller units called subners Subnets provide extra flexibility

for network administrators For example assume that network has been assigned class address

and all the nodes on the network currently conform to class address format Then assume that

the dotted decimal representation of this networks address is 128.10.0.0 all zeros in the host field

all the addresses other basic of an address specifies the entire network Rather than change to some

18-4 Internetworking Technology Overview Network Layer

network number the administrator can subdivide the network using subnetting This is done by

borrowing bits from the host portion of the address and using them as subnet field as shown in

Figure 18-4

Class address before subnetting

Class

Network Host

Class address after subnetting

Class 10

Network Subnet Host

Figure 18-4 Subnet Addresses

If network administrator has chosen to use eight bits of subnetting the third octet of class IP

address provides the subnet number In our example address 128.10.1.0 refers to network 128.10

subnet address 128.10.2.0 refers to network 128.10 subnet and so on

The number of bits borrowed for the subnet address is variable To specify how many bits are used

format and as IP IP provides the subnet mask Subnet masks use the same representation technique

bits that the host field For addresses Subnet masks have ones in all bits except those specify

for class address 34.0.0.0 is example the subnet mask that specifies eight bits of subnetting

255.255.0.0 The subnet mask that specifies 16 bits of subnetting for class address 34.0.0.0 is

255.255.255.0 Both of these subnetmasks are shown in Figure 18-5

Class 34.0.0.0 address oOiooHi

Subnet mask 255.255.0.0 subnet bits

ClassA 34.0.0.0 address

Subnet mask 255.255.255.0 16 subnet bits

Figure 18-s Sample Subnet Mask

Internet Protocols 18-5 Network Layer

On some media such as IEEE 802 LANs media addresses and IP addresses are dynamically

discovered through the use of two other members of the Internet protocol suite the Address

Resolution Protocol ARP and the Reverse Address Resolution Protocol RARP ARP uses broadcast messages to determine the hardware Media Access Control MAC-layer address

corresponding to particular internetwork address ARP is sufficiently generic to allow use of IP with of virtually any type underlying media-access mechanism RARP uses broadcast messages to

determine the Internet address associated with particular hardware address RARP is particularly

to diskless important nodes which may not know their internetwork address when they boot

nterret Routig

devices in the Routing Internet have traditionally been called gateways an unfortunate term

because elsewhere in the industry the term applies to device with somewhat different

functionality Gateways which we will call routers from this point on within the Internet are

organized hierarchically Some routers are used to move information through one particular group of networks under the same administrative authority and control such an entity is called an

autonomous system Routers used for information exchange within autonomous systems are called

interior routers and they use variety of interior gateway protocols IGPs to accomplish this

purpose Routers that move information between autonomous systems are called exterior routers

and use an exterior for this they gateway protocol purpose The Internet architecture is shown in Figure 18-6

Autonomous system Autonomous system

EExterior gateway

Interior gateway

Figure 18-6 Internet Architecture

IP routing protocols are dynamic Dynamic routing calls for routes to be calculated at regular

intervals software in the by routing devices This contrasts with static routing where routes are

established by the network administrator and do until the not change network administrator changes

them An IP table consists of destination address/next routing hop pairs sample entry shown in Figure 18-7 is interpreted as meaning to get to network 34.1.0.0 subnet on network 34 the next stop is the node at address 54.34.23.12

18-6 Internetworking Technology Overview Network Layer

Destination Next address hop

34.1.0.0 54.34.23.12

78.2.0.0 54.34.23.12

147.9.5.0

17.12.0.0

54.32.12.10

Figure 18-1 IP Routing Table

IP routing specifies that IP datagrams travel through internetworks one hop at time The entire

route is not known at the outset of the journey Instead at each stop the next destination is calculated

by matching the destination address within the datagram with an entry in the current nodes routing

table Each nodes involvement in the routing process consists only of forwarding packets based on

internal information regardless of whether the packets get to their final destination In other words

IP does not provide for error reporting back to the source when routing anomalies occur This task

is left to another Internet protocol the Internet Control Message Protocol ICMP

UCMP

ICMP performs number of tasks within an IP internetwork The principal reason it was created was

for reporting routing failures back to the source In addition ICMP provides helpful messages such

as the following

Echo and reply messages to test node reachability across an internetwork

Redirect messages to stimulate more efficient routing

Time exceeded messages to inform sources that datagram has exceeded its allocated time to

exist within the internetwork

Router advertisement and router solicitation messages to determine the addresses of routers on

directly attached subnetworks

discover the subnet mask more recent addition to ICMP provides way for new nodes to currently IP used in an internetwork All in all ICMP is an integral part of any implementation particularly

those that run in routers

RIP is discussed in Other chapters of this book discuss specific IP routing protocols Chapter 23 Interior Routing Information Protocol IGRP is discussed in Chapter 24 Gateway Routing Protocol and Enhanced Interior Gateway Routing Protocol OSPF is discussed in Chapter 25 Exterior and Open Shortest Path First EGP is discussed in Chapter 26 Gateway Protocol BGP

is also official IP is discussed in Chapter 27 Border Gateway Protocol IS-IS an routing protocol

and is discussed in Chapter 28 OSI Routing

RDP

and solicitation The ICMP Router Discovery Protocol IRDP uses router advertisement router discover addresses of attached subnets messages to routers on directly

Internet Protocols 18-7 Transport Layer

The way IRDP works is that each router periodically multicasts router advertisement messages from

each of its interfaces Hosts discover the addresses of routers on the directly attached subnet by

listening for these messages Hosts can use router solicitation messages to request immediate

advertisements rather than waiting for unsolicited messages

IRDP offers several advantages over other methods of discovering addresses of neighboring routers

Primarily it does not require hosts to recognize routing protocols nor does not it require manual

configuration by an administrator

Router advertisement messages allow hosts to discover the existence of neighboring routers but not

which router is best to reach destination If host particular uses poor first-hop router to reach

it receives redirect better choice particular destination message identifying

Transport Layer

The Internet transport layer is implemented by TCP and the User Data gram Protocol UDP TCP

provides connection-oriented data transport while UDP operation is connectionless

Transrnisson ControU Protoc TCP

TCP provides full-duplex acknowledged and flow-controlled service to upper-layer protocols It

in moves data continuous unstructured byte stream where bytes are identified by sequence

numbers TCP can also support numerous simultaneous upper-layer conversations The TCP packet

format is shown in Figure 18-8

Source port Destination port

Sequence number

Acknowledgment number

Data offset Reserved Flags Window

Checksum Urgent pointer

Options padding

Data variable

Figure 188 TCP Packet Format

The source port and destination port fields identify the points at which upper-layer source and

destination processes receive TCP services

18-8 Internetworking Technology Overview Upper-Layer Protocols

The sequence number field usually specifies the number assigned to the first byte of data in the

current Under certain it can also be used to initial message circumstances identify an sequence number to be used in the upcoming transmission

The number acknowledgment field contains the sequence number of the next byte of data the sender

of the packet expects to receive

The data offset field indicates the number of 32-bit words in the TCP header

The reserved field is reserved for future use by protocol designers

The flags field carries variety of control information

The window field the size of the senders receive window buffer specifies that is space available for incoming data

The checksum field indicates whether the header was damaged in transit

The urgent pointer field points to the first urgent data byte in the packet

The options field specifies various TCP options

The data field contains upper-layer information

User Datagram Protocol UDP

UDP is much simpler protocol than TCP and is useful in situations where TCPs powerful mechanisms reliability are not necessary The UDP header has only four fields source port destination and port length UDP checksum The source and destination port fields serve the same

functions as they do in the TCP header The length field specifies the length of the UDP header and and the checksum data field allows packet integrity checking The UDP checksum is optional

Upper4ayer ProtocoQs

The Internet protocol suite includes many upper-layer protocols representing wide variety of

applications including network management file transfer distributed file services terminal

emulation and electronic mail Table 18-1 maps the best-known Internet upper-layer protocols to

the applications they support

Table 18-1 Internet Protocol/Application Mapping

Application Protocols

File transfer FTP

Terminal emulation Telnet

Electronic mail SMTP

Network management SNTvIP

Distributed file services NFS XDR RPC Windows

The File Transfer Protocol FTP provides way to move files between computer systems Telnet

allows virtual terminal emulation The Simple Net-work Management Protocol SNMP is network

management protocol used for reporting anomalous network conditions and setting network

threshold values Windows is popular protocol that permits intelligent terminals to communicate

with remote computers as if they were directly attached Network File System SExternal Data

Representation XDR and Remote Procedure Call RPC combine to allow transparent access to

Internet Protocols 18-9 Upper-Layer Protocols

remote network resources The Simple Mail Transfer Protocol SMTP provides an electronic mail

transport mechanism These and other network applications use the services of TCP/IP and other

lower-layer Internet protocols to provide users with basic network services

18-10 Internetworking Technology Overview 19

NetWare ProtocoDs

Background

NetWare is network operating system NOS and related support services environment created by

Novell Inc and introduced to the market in the early 980s Then networks were small and

predominantly homogeneous local-area network LAN workgroup communication was new and the idea of personal computer PC was just becoming popular

Much of NetWares networking technology was derived from Xerox Network Systems XNS networking system created by Xerox Corporation in the late 970s For more information on XNS

see Chapter 22 Xerox Network Systems

By the early 1990s NetWares NOS market share had risen to between 50 and 75 percent With over

500000 NetWare networks installed worldwide and an accelerating movement to connect networks

to other networks NetWare and its supporting protocols often coexist on the same physical channel

with many other popular protocols including TCP/IP DECnet and AppleTalk

Technoogy Basics

As NOS environment NetWare specifies the upper five layers of the OSI reference model It

provides file and printer sharing support for various applications such as electronic mail transfer and

database access and other services Like other NOSs such as the Network File System NFS from

Sun Microsystems Inc and LAN Manager from Microsoft Corporation NetWare is based on

client-server architecture In such architectures clients sometimes called workstations request

certain services such as file and printer access from servers

Originally NetWare clients were small PCs while servers were slightly more powerful PCs As

NetWare became more popular it was ported to other computing platforms Currently NetWare

clients kind of and servers may be represented by virtually any computer system from PCs to mainframes

primary characteristic of the client-server system is that remote access is transparent to the user

This is which local accomplished through remote procedure calls process by computer program

running on client sends procedure call to remote server The server executes the remote

procedure call and returns the requested information to the local computer client

Figure 19-1 illustrates simplified view of NetWares best-known protocols and their relationship to

the OSI reference model With appropriate drivers NetWare can run on any media-access protocol

The figure lists those media-access protocols currently supported with NetWare drivers

NetWare Protocols 19-1 Media Access

OSI reference model NetWare

Applications RPC based

NetWare application Core LU 62 NetWare Protocol support NetBlOS shell emulator NCP client RPC

IPX

Token Ethernet Ring/ IEEE FDDI ARCnet PPP IEEE 8023 802.5

Figure 19-1 NetWare and the OSI Reference Model

Metha Access

NetWare runs on Ethernet/IEEE 802.3 Token Ring/IEEE 802.5 Fiber Distributed Data Interface FDDI and ARCnet For information on Ethernet/IEEE 802.3 see Chapter Ethernet/IEEE 802.3 For information on Token Ring/IEEE 802.5 see Chapter Token Ring/IEEE 802.5 For

Interface NetWare also works information on FDDI see Chapter Fiber Distributed Data over

Protocol is synchronous wide-area network WAN links using the Point-to-Point PPP PPP

discussed in more detail in Chapter Point-to-Point Protocol

all three Attached Resource Computer Network ARCnet is simple network system that supports and primary media twisted pair coaxial cable and fiber-optic cable and two topologies bus star

It was developed by Datapoint Corporation and introduced in 1977 Although ARCnet has not

attained the popularity enjoyed by Ethernet and Token Ring its low cost and flexibility have resulted

in many loyal supporters

Network Layer

device to be Internet Packet Exchange IPX is Novells original network-layer protocol When

communicated with is located on different network IPX routes the information to the destination

through any intermediate networks Figure 19-2 shows the IPX packet format

19-2 Internetworking Technology Overview Network Layer

IPX packet structure

Checksum

Packet length

Transport control Packet type

Destination network

Destination node

Destination socket

Source network

Source node

Source socket

Upper-layer data

Figure 19-2 IPX Packet Format

The IPX packet begins with 16-bit checksum field that is set to is

16-bit packet length field specifies the lengthin bytesof the complete IPX datagram IPX packets can be any length up to the media maximum transfer unit MTU size There is no packet fragmentation

field the has The 8-bit transport control indicates the number of routers packet passed through

When the value of this field reaches 15 the packet is discarded under the assumption that routing loop might be occurring

receive the information The 8-bit packet type field specifies the upper-layer protocol to packets

values for this field are Packet and Two common which specifies Sequenced Exchange SPX 17 the Protocol which specifies NetWare Core NCP

The destination network destination node and destination socket fields specify destination information

The source network source node and source socket fields specify source information

The upper-layer data field contains information for upper-layer processes

of Although IPX was derived from XNSit has several unique features From the standpoint routing difference the encapsulation mechanisms of these two protocols are the most important

and data into Encapsulation is the process of packaging upper-layer protocol information frame

in For Ethernet XNS uses standard Ethernet encapsulation whereas IPX packets are encapsulated

Ethernet Version 2.0 or IEEE 802.3 without the IEEE 802.2 information that typically accompanies these frames Figure 19-3 illustrates Ethernet standard IEEE 802.3 and IPX encapsulation

in standard IEEE 802.3 frames It also Note NetWare 4.0 supports encapsulation of IPX packets which extends the IEEE 802.2 supports SubNetwork Access Protocol SNAP encapsulation Ethernet headers by providing type code similar to that defined in the specification

NetWare Protocols 19-3 Transport Layer

Ethernet Standard IEEE 802.3 IPX

Destination address Destination address Destination address

Source address Source address Source address

Type Length Length

Upper-layer 802.2 header

data IPX data

802.2 data

CRC CRC CRC

Figure 19-3 Ethernet IEEE 8a2.3 and IPX Encapsulation Formats

To route packets in an internetwork IPX uses dynamic routing protocol called the Routing

Information Protocol RIP Like XNS RIP derived from work done at Xerox for the XNS protocol

family Today RIP is the most commonly used interior gateway protocol IGP in the Internet

community large international network environment providing connectivity to virtually every

research institution government agency and university and many private businesses in the United

States as well as many foreign organizations For more detailed information on RIP see Chapter 23 Routing Information Protocol

In addition to the difference in encapsulation mechanisms Novell also added protocol called the Service Advertisement Protocol allows nodes SAP to its IPX protocol family SAP that provide

services such as file servers and print servers to advertise their addresses and the services they provide

Novell also supports IBMs Logical Unit LU 6.2 network addressable unit NAU LU 6.2 allows

peer-to-peer connectivity across IBM communication environments Using NetWares LU 6.2

capability NetWare nodes can exchange information across an IBM network NetWare packets are

encapsulated within LU 6.2 packets for transit across the IBM network

Transport Layer

Packet Sequenced Exchange SPX is the most commonly used NetWare transport protocol Novell derived this protocol from XNS Sequenced Packet Protocol SPP As with the Transmission Control Protocol and TCP many other transport protocols SPX is reliable connection-oriented

protocol that supplements the datagram service provided by layer protocols

Novell also offers Internet Protocol IF support in the form of User Datagram Protocol UDPIP

encapsulation of other Novell packets such as SPXIPX packets IPX datagrams are encapsulated

inside UDP/IP headers for transport across an IF-based internetwork For more information on UDP

and the Internet protocols in general see Chapter 18 Internet Protocols

UpperLayer Protocos

NetWare wide supports variety of upper-layer protocols but several are somewhat more popular than others The NetWare shell runs in clients often called workstations in the NetWare community

and intercepts application I/O calls to determine whether they require network access for

satisfaction If the so NetWare shell packages the requests and sends them to lower-layer software

for processing and network transmission If not they are simply passed to local 110 resources Client

19-4 Internetworking Technology Overview Upper-Layer Protocols

calls applications are unaware of any network access required for completion of application redirection NetWare Remote Procedure Call NetWare RPC is another more general mechanism

supported by Novell

The NetWare Core Protocol NCP is series of server routines designed to satisfy application requests coming from for example the NetWare shell Services provided by NCP include file

acess printer access name management accounting security and file synchronization

NetWare also supports the Network Basic Input/Output System NetBIOS session-layer interface

specification from IBM and Microsoft NetWares NetBIOS emulation software allows programs

written to the industry-standard NetBIOS interface to run within the NetWare system

NetWare application-layer services include NetWare Message Handling Service NetWare MHS

Btrieve NetWare Loadable Modules NLMs and various IBM connectivity features NetWare

electronic mail Btrieve is Novells MHS is message delivery system that provides transport

implementation of the binary tree btree database access mechanism NLMs are implemented as

add-on modules that attach into the NetWare system NLMs for alternate protocol stacks

communication services database services and many other services are currently available from

Novell and third parties

NetWare Protocols 19-5 Upper-Layer Protocols

19-6 Internetworking Technology Overview CHAPTER 20

OS ProtocoDs

Background

In the early days of intercomputer communication networking software was created in haphazard

ad hoc fashion When networks grew sufficiently popular the need to standardize the by-products of

network software and hardware development became clear Standardization it was believed would

allow vendors to create hardware and software systems that could communicate with one another

even if the underlying architectures were dissimilar With this goal in mind the International

Organization for Standardization ISO began development of the Open Systems Interconnection OSI reference model The OSI reference model was completed and released in 1984

Today the OSI reference model discussed in detail in Chapter Introduction to Internetworking

is the worlds most promInent networking architecture model It is also the most popular tool for

learning about networks The OSI protocols on the other hand have had long gestation period

While OSI implementations are not unheard of the OSI protocols have not yet attained the

popularity of many proprietary for example DECnet and AppleTalk and de facto for example the

Internet protocols standards

TechnoHogy Bascs

The world of OSI networking has unique terminology

End system ES refers to any nonrouting network device

Intermediate system IS refers to router

be Area is group of contiguous networks and attached hosts that are specified to an area by

network administrator or manager

Domain is collection of connected areas Routing domains provide full connectivity to all end

systems within them

Media Access

Like several other modem seven-layer protocol stacks the OSI stack includes many of todays

popular media-access protocols This allows other protocol stacks to exist alongside OSI on the same media OSI includes IEEE 802.2 IEEE 802.3 IEEE 802.5 FDDI X.21 V.35 X.25 and others.Most

of these OSI media-access protocols are discussed elsewhere in this publication

OSI Protocols 20-1 Network Layer

Network Layer

OSI offers both connectionless and connection-oriented network layer service The

connectionless service is described in ISO 8473 usually referred to as Connectionless Network Protocol or CLNP The connection-oriented service sometimes called Connection-Oriented Packet-Level Network Service or CONS is described in ISO 8208 X.25 Protocol sometimes referred to as Connection-Mode Net-work Protocol or CMNP and ISO 8878 which describes how

to use ISO 8208 to provide OSI connection-oriented service An additional document ISO 8881 describes how to run the X.25 Packet-Level Protocol over IEEE 802 local-area networks LANs

OSI also specifies several routing protocols which are discussed in Chapter 28 OSI Routing

X.25 is discussed in Chapter 12 X.25

In addition to the previously mentioned protocol andservice specifications other relevant OSI

network-layer documents include

ISO 8648 This document is usually referred to as the internal organization of the network layer

IONL It describes how the network layer can be divided into three separate and distinct

sublayers to allow support for different subnetwork types

ISO 8348This document is usually called the network service definition It describes the

connection-oriented and connectionless services provided by the OSI network layer Network

layer addressing is also defined in this document The connectionless-mode service definition

and the addressing definition were previously published as separate addenda to ISO 8348

however the 1993 version of ISO 8348 folds all of the addenda into single document

ISO TR 9575This document describes the framework concepts and terminology used in OSI

routing protocols

ISO TR 9577This document describes how to discriminate between multiple network-layer

protocols running on the same medium Such discrimination is necessary because unlike other

protocols051 network-layer protocols cannot be identified through protocol ID or similarfield

at the link layer

Connectioness Servce

As its name suggests CLNP is connectionless datagram protocol used to carry data and error indications Functionally it is quite similar to the Internet Protocol IP described in Chapter 18 Internet Protocols It has no facilities for error detection or correction relying on the transport

layer to provide these services as appropriate It has only one phase called data transfer Each

invocation of service primitive is independent of all other invocations requiring all address

information to be completely contained within the service primitive

While CLNP defines the actual protocol performing typical network-layer functions Connectionless

Network Service CLNS describes service provided to the transport layer in which request to

transfer data receives best effort delivery Such delivery does not guarantee that data will not be

lost corrupted misordered or duplicated Connectionless service assumes that the transport layer

will correct such problems as necessary CLNS does not provide any form of connection information and or state connection setup is not performed Because CLNS provides transport layers with the service interface to CLNP CLNS and CLNP are often discussed together

In the United States federal agencies use the Government Open Systems Interconnection Profile

GOSIP specification to ensure interoperability of CLNS network products GOSJP requires certification of CLNP over LANs andX.25

20-2 Internetworking Technology Overview Network Layer

Connection-Oriented Service

OSI connection-oriented network service is specified by ISO 8208 and ISO 8878 OSI uses the X.25

Packet-Level Protocol for connection-oriented data movement and error indications Six services are

provided to transport-layer entities one for connection establishment one for connection release

and four for data Services invoked combination transfer are by some of four primitives request

indication response and confirmation The four primitives interact as shown in Figure 20-1

ES1 ES2

Figure 20-1 OSI Primitives

At time t- ES ls transport layer sends request primitive to ES ls network layer This request is

placed onto ES ls subnetwork by lower-layer subnetwork protocols and is eventually received by

ES which sends the information up to the network layer At time t-2 ES 2s network layer sends

an indication primitive to its transport layer After required upper-layer processing for this packet is

initiates sent from the complete ES response to ES by using response primitive transport

layer to the network layer The response which occurs at time t-3travels back to ES which sends the information up to the network layer where confirm primitive is generated and sent to the

transport layer at time t-4

Addressing

the The OSI network service is provided to the transport layer through conceptual point on

There is network/transport layer boundary known as network service access point NSAP one

NSAP per transport entity

Each NSAP can be individually addressed in the global OSI internetwork through its NSAP address end have often colloquially and imprecisely known as an NSAP An OSI system can multiple

NSAP addresses in which case the addresses usually differ only in the last byte known as the

n-selector

associated with It is also useful to address systems network layer without being specific transport when entityfor instance when system participates in routing protocols or addressing an network address intermediate system router Such addressing is done via special known as

title is identical to an but uses the network entity NET NET structurally NSAP address special have unlike n-selector value 00 Most end systems and intermediate systems only single NET

intermediate that is IP routers which usually have one address per interface However an system NETs participating in multiple areas or domains can choose to have multiple

OSI Protocols 20-3 Transport Layer

NETs and NSAP addresses are hierarchical addresses Addressing hierarchies facilitate both administration by allowing multiple levels of address administration and routing by encoding network topology information An NSAP address is first separated into two parts the initial domain

part IDP and the dwnain specic part DSP The IDP is then further divided into the authority

and format identifier AFI and the initial domain identifier IDI

The AR provides information about the structure and content of the IDI and DSP fields including

whether the WI is of variable length and whether the DSP uses decimal or binary notation The IDI

specifies an entity that can assign values to the DSP portion of the address

The DSP is then further subdivided by the authority responsible for its administration Typically

another administrative authority identifier follows allowing address administration to be further

delegated to subauthorities Following that comes information used for routing such as the routing

domain the area with the routing domain the station ID within the area and the selector within the

station Figure 20-2 illustrates the OSI address format

IDP DSP

AFI IDI Area Station Selector

Fiqure 20-2 OSI Address Format

Transport Layer

As with the OSI network both layer connectionless and connection-oriented transport services are offered There are actually five connection-oriented OSI transport protocols TPO TP1 TP2 TP3

and TP4 All but TP4 work only with OSIs connection-oriented network service TP4 works with

both connection-oriented and connectionless services

TPO is the OSI simplest comiection-oriented transport protocol Of the classical transport layer

functions it performs only segmentation and reassembly This means that TPO will note the smallest

maximum size protocol data unit PDU supported by the underlying subnetworks and will break

the transport packet into smaller pieces that are not too big for network transmission

In addition to segmentation and reassembly TP1 offers basic error recovery It numbers all PDUs

and resends those that are unacknowledged TP1 can also reinitiate connections when excessive unacknowledged PDUs occur

TP2 can multiplex and demultiplex data streams over single virtual circuit This capability makes TP2 particularly useful over public data networks PDNs where each virtual circuit incurs Like separate charge TPO and TP TP2 also segments and reassembles PDUs

TP3 combines the features or TP1 and TP2

TP4 is the most popular 051 transport protocol TP4 is similar to the Internet protocol suites Transmission Control Protocol TCP and in fact was based on TCP In addition to TP3s features

TP4 reliable provides transport service It assumes network in which problems are not detected

20-4 Internetworking Technology Overview Upper-Layer Protocols

Upper4ayer Protocos

Principal OSI upper-layer protocols are shown in Figure 20-3

OSI reference model

CMIP DS FTAM MHS VTP Application

ASN.1 ACSE ROSE RTSE

Presentation 051 presentation layer

Session OSI session layer

Figure 20-3 Principal OSI Upper-Layer Protocols

Session Layer

The OSI session-layer protocol turns the data streams provided by the lower four layers into sessions mechanisms include conversation by implementing various control mechanisms These accounting

control that is determining who can talk when and session parameter negotiation

of which the Session conversation control is implemented by use of token the possession provides

that right to communicate The token can be requested and ESs can be given priorities provide for

unequal token use

Presentation Layer

The OSI presentation layer is typically just pass-through protocol for information from adjacent

layers Although many people believe that Abstract Syntax Notation ASN.1 is OSIs

presentation-layer protocol ASN.1 is used for expressing data formats in machine-independent

format This allows communication between applications on diverse computer systems ESs in

manner transparent to the applications

Application Layer

well service elements The OSI application layer includes actual applications as as application

lower The three most ASEs ASEs allows easy communication from applications to layers Remote Service important ASEs are Association Control Service Element ACSE Operations Element ROSE and Reliable Transfer Service Element RTSE ACSE associates application communication names with one another in preparation for application-to-application ROSE

in similar implements generic request-reply mechanism that permits remote operations manner

to that of remote procedure calls RPCs RTSE aids reliable delivery by making session-layer

constructs easy to use

OSI Protocols 20-5 Upper-Layer Protocols

Five OSI applications receive the most attention

Common Protocol network Management Information CMIPOSIs management protocol Like SNMP see Chapter 32 Simple Network Management Protocol for more information and NetView see Chapter 33 IBM Network Management for more information it allows of exchange management information between ESs and management stations which are also ESs

Services Derived from the Consultative Directory DS Committee for International Telegraph and Telephone CCITT X.500 specification this service provides distributed database useful capabilities for upper-layer node identification and addressing

File and Transfer Access Management FTAMOSIs file transfer service In addition to

classical file transfer for which FTAM provides numerous options FTAM also offers distributed

file access facilities in the of NetWare spirit from Novell Inc or Network File System NFS from Sun Microsystems Inc

Message Handling Systems MHS Provides an underlying transport mechanism for electronic messaging applications and other applications desiring store-and-forward services Although similar they accomplish purposes MHS is not to be confused with Novells NetWare MHS see Chapter 19 NetWare Protocols for more information

Virtual Terminal Protocol VTP Provides terminal emulation In other words it allows

to to remote if it computer system appear ES as were directly attached terminal With VTP users can for example run remote jobs on mainframes

20-0 Internetworking Technology Overview CHA TER 21

Banyan VINES

Background

Banyan Virtual Network System VINES implements distributed network operating system based

on proprietary protocol family derived from Xerox Corporations Xerox Network Systems XNS

protocols see Chapter 22 Xerox Network Systems VINES uses client-server architecture in

such file and from with which clients request certain services as printer access servers Along Novells NetWare IBMs LAN Server and Microsofts LAN Manager VINES is one of the best- networks known distributed system environments for microcomputer-based

TechnoHogy Bascs

The VINES protocol stack is shown in Figure 21-1

OSI

reference

model VINES protocol

File Print Other StreetTalk services services applications

RPC

IPC SPP datagram stream

ARP

VIP RTP

ICP

Media-access protocols

Figure 21-1 VINES Protocol Stack

Banyan VINES 21-1 Media Access

Meda Access

The lower two layers of the VINES stack are implemented with variety of well-known media- access Data mechanisms including High-Level Link Control HDLC see Chapter 11 Data Control and Synchronous Link DerivativesX.25 see Chapter 12 X.25 Ethernet see Chapter Ethernet/IEEE 802.3 and Token Ring see Chapter Token Ring/IEEE 802.5

Network Layer

VINES uses the VINES Intern etwork Protocol VIP to perform layer activities including

internetwork routing VINES also its own Address Resolution Protocol supports ARP its own version of the Protocol Routing Information RIP called the Routing Table Protocol RTP and the Internet Control Protocol which ICP provides exception handling and special routing cost

information ARP ICP and RTP packets are encapsulated in VIP header

VNES nternetwork Protoc VP VINES network-layer addresses are 48-bit entities subdivided into network 32 bits and subnetwork The 16 bits portions network number is better described as server number since it is derived from the directly servers key hardware module that identifies unique number and the software

for that options server The subnetwork portion of VINES address is better described as host

since it is number used to identify hosts on VINES networks Figure 21-2 illustrates the VINES address format

32 33 48

Network number Subnet number

Server number Host number

Figure 21-2 VINES Address Format

The network number identifies VINES logical network which is represented as two-level tree

with the root at service node Service nodes which are usually servers provide address resolution

and services to routing clients which represent the leaves of the tree The service node assigns VIP

addresses to clients

When client is powered it broadcasts for All on request servers servers that hear the request The client chooses the respond first response and requests subnetwork host address from that server The server responds with an address consisting of its own network address derived from its concatenated with key subnetwork host address of its own choosing Client subnetwork addresses are typically assigned sequentially starting with 8001H Server subnetwork addresses are The VINES always address selection process is shown in Figure 21-3

21-2 Internetworking Technology Overview Network Layer

Broadcast

any servers

______

Client Server

Server Please

assign me an address

Client Server Server2

Your address is Server Node 8001

Client Server Server

Figure 21-3 VINES Address Selection Process

Dynamic address assignment is not unique in the industry AppleTalk also uses this processbut it is certainly not as common as static address assignment Since addresses are chosen exclusively by the of the there particular server whose address is unique as result of uniqueness hardware key Internet Protocol is very little chance of duplicate address potentially devastating problem on IP and other networks

In the VINES network scheme all servers with multiple interfaces are essentially routers Clients always choose their own server as first-hop router even if another server on the same cable about other routers provides better route to the ultimate destination Clients can learn by receiving for redirect messages from their own server Since clients rely on their servers first-hop routing

VINES servers maintain routing tables to help them find remote nodes

Banyan VINES 21-3 Network Layer

VINES routing tables consist of hosticost where host pairs corresponds to network node that can be reached and cost corresponds to in delay expressed milliseconds to get to that node RTP helps VINES servers find neighboring clients servers and routers

Periodically all clients advertise both their network-layer and their Media Access Control MAClayer addresses with the equivalent of hello packet Hello packets indicate that the client is still operating and network-ready The servers themselves send routing updates to other servers

periodically Routing updates alert other routers to in node changes addresses and network topology

When VINES server receives it checks to if the packet see packet is destined for another server

or if its broadcast If the current server is the the destination server handles the request

appropriately If another server is the the destination current server either forwards the packet the directly if server is neighbor or routes it to the next server in line If the packet is broadcast the current server checks to see if the from the packet came least-cost path If not the packet is discarded If so the packet is forwarded on all interfaces except the one on which it was received This approach helps diminish the number of broadcast storms common problem in other network environments The VINES routing algorithm is shown in Figure 21-4

Figure 21-4 VINES flouting Algorithm

21-4 Internetworking Technology Overview Network Layer

The VIP packet format is shown in Figure 21-5

Field length Variable in bytes

Trans- Destination Destination Source Source Check- Packet Protocol port network subnetwork network subnetwork Data sum length control type number number number number

Figure 21-5 VIP Packet Format

The VIP packet begins with checksum field which is used to detect packet corruption

The packet length field indicates the length of the entire VIP packet

broadcast The transport control field consists of several subfields If the packet is packet two

subfield subfields are provided the class subfield bits through and the hop-count bits through the If the packet is not broadcast packet four subfields are provided the error subfield metric

subfield the redirect subfield and the hop count subfield The class subfield specifies the type of

node that should receive the broadcast For this purpose nodes are broken into various categories

of link the node is the of nodes having to do with the type of node and the type on By specifying type

to receive broadcasts the class subfield reduces the disruption caused by broadcasts The hop count

the has been The error subfield represents the number of hops router traversals packet through

subfield specifies whether the ICP protocol should send an exception notification packet to the

packets source if packet turns out to be unroutable The metric subfield is set to one by transport

entity when it needs to learn the routing cost of moving packets between service node and

neighbor The redirect subfield specifies whether the router should generate redirect when

appropriate

for which the metric or The protocol type field indicates the network- or transport-layer protocol

exception notification packet is destined

The destination network number destination subnetwork number source network number and

source subnetwork number fields provide VIP address information

Routing Tahe Protocol RIP

RTP distributes network topology information Routing update packets are broadcast periodically

by both client and service nodes These packets inform neighbors of nodes existence and also

indicate whether the node is client or service node Service nodes also include in each routing

associated with those update packet list of all known networks and the cost factors reaching networks

and table For Two routing tables are maintained table of all known networks of neighbors

service nodes the table of all known networks contains an entry for each known network except the and service nodes own network Each entry contains network number routing metric pointer

The table of contains to the entry for the next hop to the network in the table of neighbors neighbors Entries include network an entry for each neighbor service node and client node number

used to reach that subnetwork number the media-access protocol for example Ethernet node local-area network LAN address if the medium connecting the neighbor is LAN and neighbor metric

Banyan VINES 21-5 Network Layer

RTP specifies four packet types

Routing update packetsIssued periodically to notify neighbors of an entitys existence

Routing request packetsExchanged by entities when they need to learn the networks topology

quickly

information and used service nodes Routing response packets Contain topological are by to

respond to routing request packets

Routing redirect packetsProvide better path information to nodes using inefficient paths

RTP packets have four-byte header consisting of the following fields

one-byte operation type field which indicates the packet type

one-byte node type field which indicates whether the packet came from service node or nonservice node

one-byte controller type field which indicates whether the controller in the node transmitting

the RTP packet has multibuffer controller

one-byte machine type field which indicates whether the processor in the RTP sender is fast

or slow

Both the controller type and the machine type fields are used for pacing

Address Resokitou ProtocoD ARP

ARP protocol entities are classified as either address resolution clients or address resolution

services Address resolution clients are usually implemented in client nodes whereas address

resolution services are typically provided by service nodes

ARP packets have an 8-byte header consisting of two-byte packet type four-byte network

number and two-byte subnetwork number There are four packet types query request which is

for which is request an ARP service service response response to query request an

assignment request which is sent to an ARP service to request VINES internetwork address and

which is service the an assignment response sent by the ARP as response to assignment request

The network number and fields have in subnet number only meaning an assignment response packet

ARP clients and services implement the following algorithm when client starts up First the client

broadcasts the client query request packets Then each service that is neighbor of responds with service response packet The client then issues an assignment request packet to the first service that

responded to its query request packet The service responds with an assignment response packet

containing the assigned internet address

nternet Contro ProtocoD DCP

ICP defines exception notification and metric notification packets Exception notification packets

provide information about network-layer exceptions metric notification packets contain

information about the final transmission used to reach client node

Exception notifications are sent when VIP packet cannot be routed properly and the error subfield

in the VIP headers transport control field is enabled These packets also contain field identifying

the particular exception by its error code

ICP entities in service nodes generate metric notification messages when the metric subfield in the

VIP headers transport control field is enabled and the destination address in the service nodes

packet specifies one of the service nodes neighbors

21-6 Internetworking Technology Overview Transport Layer

Transport Layer

VINES provides three transport-layer services

Unreliable datagram serviceSends packets that are routed on best-effort basis but not

acknowledged at the destination

Reliable message serviceA virtual-circuit service that provides reliable sequenced and

acknowledged delivery of messages between network nodes reliable message may be

transmitted in maximum of four VIP packets

Data stream serviceSupports the controlled flow of data between two processes The data

stream service is an acknowledged virtual circuit service that supports the transmission of

messages of unlimited size

UpperLayer Protocos

As distributed network VINES uses the remote procedure call RPC model for communication

between clients and servers RPC is the foundation of distributed service environments The NetRPC

that allows to remote protocol layers and provides high-level programming language access

services in manner transparent to both the user and the application

well which At layer VINES offers file-service and print-service applications as as StreetTalk

provides globally consistent name service for an entire internetwork

under several VINES also provides an integrated applications development environment operating

third systems including DOS and UNIX This development environment allows parties to develop

both clients and services that run in the VINES environment

Banyan VINES 21-7 Upper-Layer Protocols

21-8 Internetworking Technology Overview CHAPTER 22

Xerox Network Systems

Background

The Xerox Network Systems XNS protocols were created by Xerox Corporation in the late 1970s

and early l980s They were designed to be used across variety of communication media

and Several resemble the Internet Protocol and processors office applications XNS protocols IP Transmission Control Protocol TCP protocols developed by the Defense Advanced Research Projects Agency DARPA for the U.S Department of Defense DoD See Chapter 18 Internet

Protocols for more information on these and related protocols All XNS protocols meet the basic

design objectives of the OSI reference model

Because of its availability and early entry into the market XNS was adopted by most of the early

LAN companies including Novell Inc Ungermann-B ass Inc now part of Tandem Computers

and 3Com Corporation Each of these companies has since made various changes to the XNS

protocols Novell added the Service Advertisement Protocol SAP to permit resource advertisement

and modified the OSI layer protocols which Novell renamed IPX for Internetwork Packet modified Exchange to run on IEEE 802.3 rather than Ethernet networks Ungermann-B ass RIP to

also made the support delay as well as hop count Other small changes were Over time XNS

implementations for PC networking have become more popular than XNS as it was designed by Xerox

Technoogy Basics

the of Although the XNS design objectives are the same as the OSI reference model XNS concept the reference model protocol hierarchy is somewhat different from that provided by OSI rough

comparison is shown in Figure 22-1

Xerox Network Systems 22-1 Media Access

XNS

OSI Level

Level

______

Level

Figure 22-1 XNS and the OSI Reference Model

As seen in Xerox Figure 22-1 provided five-level model of packet communications Level

corresponds to OSI and link roughly layers handling access and bit-stream manipulation Level corresponds roughly to the portion of OSI layer that pertains to network traffic Level

corresponds to the of OSI that roughly portion layer pertains to internetwork routing and to OSI layer which handles interprocess communication Levels and correspond roughly to the upper two layers of the OSI data model handling structuring process-to-process interaction and XNS has applications no protocol corresponding to OSI layer the session layer

Media Access

Although XNS documentation mentions X.25 Ethernet and High-Level Data Link Control

XNS does not define what it HDLC expressly refers to as level protocol Like many other protocol suites XNS leaves media access an issue open implicitly allowing any such protocol to host the of transport XNS packets over physical medium

Network Layer

The XNS network-layer protocol is called the Internet Data Protocol gram IDP IDP performs standard layer functions including and end-to-end logical addressing datagram delivery across an internetwork The format of an IDP packet is shown in Figure 22-2

22-2 Internetworking Technology Overview Network Layer

Field length in bytes 0-546

ABCD Data

Checksum

Length

Transport control

Packet type Destination network

Destination host

Destination socket Source network

Source host

Source socket

Figure 22-2 lOP Packet Format

The first field in an IDP packet is 16-bit checksum field which helps gauge the integrity of the packet after it traverses the internetwork

The 16-bit length field carries the complete length including checksum of the current datagram

The 8-bit control field contains and subfields transport hop count maximumpacket lifetime MPL

The hop count subfield is initialized to zero by the source and incremented by one as the datagram

reaches the is discarded the passes through router When the hop count field 16 datagram on assumption that routing ioop is occurring The MPL subfield provides the maximum amount of time in seconds that packet can remain on the intemetwork

The 8-bit packet type field specifies the format of the data field

XNS source and destination network addresses each have three fields 32-bit network number that uniquely identifies network in an internetwork 48-bit host number that is unique across all hosts ever manufactured and 16-bit socket number that uniquely identifies socket process within particular host IEEE 802 addresses are equivalent to host numbers so hosts that are connected to more than one IEEE 802 network have the same address on each segment This makes network numbers redundant but nevertheless useful for routing Certain socket numbers are well known meaning that the service performed by the software using them is statically defined All other socket numbers are reusable

XNS supports Ethernet Version 2.0 encapsulation for Ethernet and three types of encapsulation for Token Ring 3Com SubNet Access Protocol SNAP and Ungermann-Bass

XNS supports unicast point-to-point multicast and broadcast packets Multicast and broadcast addresses are further divided into directed and global types Directed multicasts deliver packets to destination multicast members of the multicast group on the network specified in the network address Directed broadcasts deliver packets to all members of specified network Global

entire whereas multicasts deliver packets to all members of the group within the internetwork global broadcasts deliver packets to all internetwork addresses One bit in the host number indicates single versus multicast address All ones in the host field indicate broadcast address

To route packets in an internetwork XNS uses dynamic routing scheme called the Routing Protocol Information Protocol RIP Today RIP is the most commonly used Interior Gateway

IGP in the Internet community which is large international network environment providing

Xerox Network Systems 22-3 Transport Layer

connectivity to many research institutions government agencies and universities and private

businesses in the United States See Chapter 23 Routing Information Protocol for more information on RIP

Transport Layer

OSI transport-layer functions are implemented by several protocols Each of the following protocols

is described in the XNS specification as level protocol

The Sequenced Packet Protocol SPP provides reliable connection-based flow-controlled packet

transmission behalf of client It is similar in function the Internet Protocol suites on processes to Transmission Control Protocol TCP and the OSI protocol suites Transport Protocol TP4 See

Chapter 18 Internet Protocols for more information on TCP and Chapter 20 OSI Protocols for more information on TP4

SPP includes which is used order and determine if Each packet sequence number to packets to any

have been duplicated or missed SPP packets also contain two 16-bit connection identifiers One

connection identifier is specified by each end of the connection Together the two connection

identifiers client uniquely identify logical connection between processes

SPP packets cannot be longer than 576 bytes Client processes can negotiate use of different packet

size during connection establishment but SPP does not define the nature of this negotiation

The Packet Exchange Protocol PEP is request-response protocol designed to have greater

reliability than simple datagram service as provided by IDP for example but less reliability than

SPP PEP is functionally similarto the Internet Protocol suites User Data gram Protocol UDP See

Chapter 18 Internet Protocols for more information on UDP PEP is single-packet based

providing retransmissions but no duplicate packet detection As such it is useful in applications

where request-response transactions are idempotent repeatable without damaging data or where

reliable transfer is executed at another layer

The Error Protocol EP can be used by any client process to notify another client process that

network error has occurred This protocol is used for example in situations where an SPP

implementation has identified duplicate packet

Upper4ayer ProtocoDs

XNS offers several upper-layer protocols The Printing Protocol provides print services The Filing

Protocol provides file-access services The Clearinghouse Protocol provides name services Each of

these three protocols runs on top of the Courier Protocol which provides conventions for data

structuring and process interaction

XNS also defines level protocols These are application protocols but since they have little to do

with actual communication functions the XNS specification does not include any pertinent definitions

the Echo Protocol is used of network nodes Finally to test the reachability XNS It is used to support

functions such as that provided by the ping command found in UNIX and other environments The

XNS specification describes the Echo Protocol as level protocol

22-4 Internetworking Technology Overview

CHAPTER 23

Routing Information Protocol

Background

The Routing Information Protocol RIP is routing protocol originally designed for Xerox PARC

and used in the Universal Protocol where it was called GWINFO Xerox Network Systems XNS and Transmission Control Protocol/Internet protocol suite RIP became associated with both UNIX Protocol TCP/IP in 1982 when the Berkeley Software Distribution BSD version of UNIX began

route which is shipping with RIP implementation referred to as routed pronounced dee RIP

is defined in the still very popular routing protocol in the Internet community formally XNS 1058 Internet Transport Protocols publication 1981 and inRequestfor Comments RFC 1988

for in their RIP has been widely adopted by personal computer PC manufacturers use networking

Maintenance also products For example AppleTalks routing protocol Routing Table Protocol basis the of known as RTMP is modified version of RIP RIP was also the for routing protocols Novell 3Com Ungennann-Bass and Banyan The Novell and 3Com RIPs are basically standard their needs Xerox RIP Ungermann-B ass and Banyan made minor modifications to RIP to serve own

Routng Tabe Format

table of the ultimate Each entry in RIP routing provides vaiiety information including metric indicates the destination the next hop on the way to that destination and metric The be in the distance in number of hops to the destination Other information can also present routing

table is shown in table including various timers associated with the route typical RIP routing

Figure 23-1

Destination Next hop Distance Timers Flags

Network Router tl 12 t3

Network Router ti t2 13

Network Router 11 t2 t3

Figure 23-1 Typical RIP Routing Table

Routing Information Protocol 23-1 Packet Format IP Implementations

RIP maintains only the best route to destination When new information provides better route

this information replaces old route information Network topology changes can provoke changes to

routes causing for example new route to become the best route to particular destination When

network topology changes occur they are reflected in routing update messages For example when

router detects link failure or router failure it recalculates its routes and sends routing update Each messages router receiving routing update message that includes change updates its tables

and propagates the change

Packet Format mpementations

Figure 23-2 shows the RIP packet format for IF implementations as specified by RFC 1058

Note Figure 23-2 shows the RIP format used for IP networks in the Internet Some other RIP

variations make slight modifications to the format and/or to the field names listed here but the basic

routing algorithm is functionally the same

Field length mbytes

Command request or response Version number Zero

Address family identifier Address

Metric

Figure 23-2 RIP Packet Format

The first field in an IP RIP packet is the command field This field carries an integer indicating either or The command the request response request requests responding system to send all or part of

its table Destinations for which is listed later in routing response requested are the packet The

response command represents reply to request or more frequently an unsolicited regular routing

update In the response packet responding system includes all or part of its routing table Regular

routing update messages include the entire routing table

The version number field the RIP version With specifies being implemented the potential for many

RIP implementations in an intemetwork this field can be used to signal different potentially

incompatible implementations

Following 16-bit field of all zeros is the address family identifier field which specifies the

particular address family being used On the Internet large international network connecting

research institutions government institutions universities and private businesses this address

family is typically IF value but other network types may also be represented

After another 16-bit field of zeros is 32-bit address field In Internet RIP implementationsthis field

typically contains an IP address

23-2 Internetworking Technology Overview Stability Features

Following two more 32-bit fields of zeros is the RIP metric which is hop count It indicates how

many internetwork hops routers must be traversed before the destination can be reached

Up to 25 occurrences of the address family identifier through metric fields are permitted to occur in

any single IP RIP packet In other words up to 25 destinations may be listed in any single RIP

packet Multiple RIP packets.are used to convey information from larger routing tables

Like other routing protocols RIP uses certain timers to regulate its performance The RIP routing

update timer is generally set to 30 seconds ensuring that each router will send complete copy of

its routing table to all neighbors every 30 seconds The route invalid timer determines how much

time must expire without router having heard about particular route before that route is

considered invalid When route is marked invalid neighbors are notified of this fact This

notification must occur prior to expiration of the route flush timer When the route flush timer

expires the route is removed from the routing table Typical initial values for these timers are 90

seconds for the route invalid timer and 270 seconds for the route flush timer

Stabilty Features

RIP specifies number of features designed to make its operation more stable in the face of rapid

network topology changes These include hop-count limit hold-downs split horizons and poison

reverse updates

HopCount Umt

RIP permits maximum hop count of 15 Any destination greater than 15 hops away is tagged as

unreachable RIPs maximum hop count greatly restricts its use in large internetworks but prevents

problem called count to infinity from causing endless network routing loops The count-to-infinity

problem is shown in Figure 23-3

Figure 23-3 Count-To-Infinity Problem

In Figure 23-3 consider what will happen if Router ls Rl link link to Network fails Ri

link Network Since examines its infonnation and sees that Router R2 has one-hop to Ri Network and knows it is directly connected to R2 it advertises two-hop path to begins routing

all traffic to Network through R2 This creates routing loop When R2 sees that Ri can now get

show that it has to Network in two hops it changes its own routing table entry to three-hop path

to Network This problem and the routing loop will continue indefinitely or until some external

boundary condition is imposed That boundary condition is RIPs hop-count maximum When the

is removed from the hop count exceeds 15 the route is marked unreachable Over time the route table

Routing Information Protocol 23-3 Stability Features

ol d- Downs

Hold-downs are used to prevent regular update messages from inappropriately reinstating route

that has gone bad When route goes down neighboring routers will detect this These routers then calculate new routes and send out routing update messages to inform their neighbors of the route

change This activity begins wave of routing updates that filter through the network

Triggered updates do not instantly arrive at every network device It is therefore possible that device that has yet to be informed of network failure may send regular update message

indicating that route that has just gone down is still good to device that has just been notified

of the network failure In this case the latter device now contains and potentially advertises

incorrect routing information

Hold-downs tell routers to hold down any changes that might affect recently removed routes for

some period of time The hold-down period is usually calculated to be just greater than the period of

time necessary to update the entire network with routing change Hold-down prevents the count-

to-infinity problem

Split Horizons

Split horizons derive from the fact that it is never useful to send information about route back in

the direction which from it came For example consider Figure 23-4

Network Network

Figure 23-4 Split Horizons

Router Ri initially advertises that it has route to Network There is no reason for Router

R2 to include this route in its update back to Ri as Ri is closer to Network The split-horizon

rule says that R2 should strike this route from any updates it sends to Ri

The split-horizon rule helps prevent two-node routing loops For example consider the case where

Ris interface to Network goes down Without split horizons R2 continues to inform Ri that it

can get to Network through Ri If Ri does not have sufficient intelligence it might actually pick

up R2s route as an alternative to its failed direct connection causing routing ioop Although hold-

downs should prevent this split horizon provides extra algorithm stability

Poison Reverse Updates

Whereas split horizons should prevent routing loops between adjacent routers poison reverse

updates are intended to defeat larger routing loops The idea is that increases in routing metrics indicate generally routing loops Poison reverse updates are then sent to remove the route and place

it in hold-down

23-4 Internetworking Technology Overview CHAPTER 24

Interior Gateway Routing Protocol and

Enhanced Interior Gateway Routing Protocol

Background

in the mid-i 980s The Interior Gateway Routing Protocol IGRP is routing protocol developed by

Cisco Systems Inc Ciscos principal goal in creating IGRP was to provide robust protocol for and of routing within an autonomous system AS having arbitrarily complex topology consisting

media with diverse bandwidth and delay characteristics An AS is collection of networks under

common administration that share common routing strategy ASs are typically given unique Center 16-bit number that is assigned by the Defense Data Network DDN Network Information NIC

Protocol In the mid-1980s the most popular intra-AS routing protocol was the Routing Information

RIP Although RIP was quite useful for routing within small- to moderate-sized relatively homogeneous internetworks its limits were being pushed by network growth In particular RIPs metric did small hop-count limit 16 restricted the size of internetworks and its single hop count information not allow for much routing flexibility in complex environments For more on RIP see robustness of Chapter 23 Routing Information Protocol The popularity of Cisco routers and the with IGRP IGRP have encouraged many organizations with large internetworks to replace RIP

Ciscos initial IGRP implementation worked in Internet Protocol IP networks IGRP was designed

to run in any network environment however and Cisco soon ported it to run in Open System Interconnection OSI Connectionless Network Protocol CLNP networks

of Cisco developed Enhanced IGRP EIGRP in the early 990s to improve the operating efficiency

IGRP EIGRP is discussed in detail later in this chapter

Tech no gy

call for IGRP is distance vector interior-gateway protocol IGP Distance vector routing protocols

intervals each router to send all or portion of its routing table in routing update message at regular

to each of its neighboring routers As routing information proliferates through the network routers

can calculate distances to all nodes within the internetwork

which send Distance vector routing protocols are often contrasted with link state routing protocols Shortest Path local connection information to all nodes in the internetwork See Chapter 25 Open Path First First and Chapter 28 OSI Routing respectively for discussion of Open Shortest

link OSPF and Intermediate System-to-Intermediate System IS-IS two popular state routing

algorithms

and load IGRP uses combination vector of metrics Internetwork delay bandwidth reliability are

factors for each all factored into the routing decision Network administrators can set the weighting

of these metrics IGRP uses either the administrator-set or the default weightings to automatically

calculate optimal routes

Interior Gateway Routing Protocol and Enhanced Interior Gateway Routing Protocol 24-1 Stability Features

and load take value IGRP provides wide range for its metrics For example reliability can on any

to 10 between and 255 bandwidth can take on values reflecting speeds from 1200 bps gigabits the 24th Wide metric per second while delay can take on any value from to to power ranges

allow satisfactory metric setting in intemetworks with widely varying performance characteristics user-definable As Most importantly the metric components are combined in algorithm result

network administrators can influence route selection in an intuitive fashion

Dual lines To provide additional flexibility IGRP permits multipath routing equal-bandwidth may

switchover the second line if run single stream of traffic in round-robin fashion with automatic to

metrics the different one line goes down Also multiple paths can be used even if the for paths are

metric is times For example if one path is three times better than another because its three lower

within certain the better path will be used three times as often Only routes with metrics that are

range of the best route are used as multiple paths

Stabilty Features

IGRP provides number of features that are designed to enhance its stability These include hold-

downs split horizons and poison reverse updates

HodDowros

Hold-downs are used to prevent regular update messages from inappropriately reinstating route

detect this via the lack of that may have gone bad When router goes down neighboring routers and send regularly scheduled update messages These routers then calculate new routes routing This of update messages to inform their neighbors of the route change activity begins wave

triggered updates that filter through the network

therefore that These triggered updates do not instantly arrive at every network device It is possible

device that has yet to be informed of network failure may send regular update message

notified indicating that route that has just gone down is still good to device that has just been of the network failure In this case the latter device would now contain and potentially advertise

incorrect routing information

Hold-downs tell routers to hold down any changes that might affect routes for some period of time

The hold-down period is usually calculated to be just greater than the period of time necessary to

update the entire network with routing change

SpUt Horzorls

Split horizons derive from the fact that it is never useful to send information about route back in

the direction from which it came For example consider Figure 24-1

Network Network

Figure 24-1 Split Horizons

24-2 Internetworking Technology Overview EIGRP

Router Ri initially advertises that it has route to Network There is no reason for Router

to include this route in its is closer R2 update back to Ri as Ri to Network The split-horizon

rule that R2 should strike this from it sends says route any updates to Ri

The split-horizon rule helps prevent routing loops For example consider the case where Ris

interface to Network down continues inform goes Without split horizons R2 to Ri that it can get to Network through If Ri does not have sufficient intelligence it may actually pick up R2s

route as an alternative to its failed direct connection causing routing loop Aithough hold-downs

should prevent this split horizons are implemented in IGRP because they provide extra algorithm

stability

Poison Reverse Updates

Whereas split horizons should prevent routing loops between adjacent routers poison reverse

updates are intended to defeat larger routing loops Increases in routing metrics generally indicate

routing loops Poison reverse updates are then sent to remove the route and place it in hold-down

In Ciscos implementation of IGRP poison reverse updates are sent if route metric has increased

by factor of .1 or greater

Timers

IGRP maintains number of timers and variables containing time intervals These include an update

timer an invalid timer hold-time period and flush timer The update timer specifies how

frequently routing update messages should be sent The IGRP default for this variable is 90 seconds

invalid in The timer specifies how long router should wait the absence of routing update messages

about specific route before declaring that route invalid The IGRP default for this variable is three

times the update period The hold-time variable specifies the hold-down period The IGRP default

for this variable is three times the update timer period plus ten seconds Finally the flush timer

indicates how much time should pass before route should be flushed from the routing table The

IGRP default is seven times the routing update period

UGRP

With Software Release 9.21 Cisco introduced an enhanced version of IGRP that combines the

advantages of link state protocols with the advantages of distance vector protocols EIGRP

incorporates the Diffusing Update Algorithm DUAL developed at SRI International by Dr J.J

Garcia-Luna-Aceves EIGRP includes the following features

Fast convergenceEIGRP uses DUAL to achieve convergence quickly router running

EIGRP stores all of its neighbors routing tables so that it can quickly adapt to alternate routes

If no appropriate route exists EIGRP queries its neighbors to discover an alternate route These

queries propagate until an alternate route is found

Variable length subnet masksEIGRP includes full support for variable length subnet masks

Subnet routes are automatically summarized on network number boundary In addition

Enhance IGRP can be configured to summarize on any bit boundary at any interface

Partial bounded updates EIGRP does not make periodic updates Instead it sends partial

updates only when the metric for route changes Propagation of partial updates is automatically

bounded so that only those routers that need the information are updated.As result of these two

capabilities EIGRP consumes significantly less bandwidth than IGRP

Interior Gateway Routing Protocol and Enhanced Interior Gateway Routing Protocol 24-3 EIGRP Technology

and Novell Multiple network-layer supportEIGRP includes support for AppleTalk IP Maintenance Protocol NetWare The AppleTalk implementation uses Routing Table RTMP to Protocol redistribute routes The IP implementation can use OSPF RIP I-JSExterior Gateway EGPor Border Gateway Protocol BGP to redistribute routes The Novell implementation can use Novell RIP or Service Advertisement Protocol SAP to redistribute routes

Compatibility with UGRP

automatic EIGRP provides compatibility and seamless interoperation with IGRP routers An

redistribution mechanism allows IGRP routes to be imported into EIGRP and EIGRP routes to be

imported into IGRP so it is possible to add EIGRP gradually into an existing IGRP network

Because the metrics for both protocols are directly translatable they are as easily comparable as if

they were routes that originated in their own ASs In addition EIGRP treats IGRP routes as extemal

routes and provides way for the network administrator to customize them

EGRP Tech noogy

EIGRP features four new technologies

Neighbor discovery/recovery

Reliable Transport Protocol

DUAL finite state machine

Protocol-dependent modules

Neighbor discovery/recovery is the process that routers use to dynamically learn about other routers

on their directly attached networks Routers must also discover when their neighbors become

unreachable or inoperative This process is achieved with low overhead by periodically sending

small hello packets As long as router receives hello packets from neighboring router it assumes

that the neighbor is functioning and they can exchange routing information

The Reliable Transport Protocol RTP is responsible for guaranteed ordered delivery of EIGRP

packets to all neighbors It supports intermixed transmission of multicast or unicast packets For

efficiency only certain EIGRP packets are transmitted reliably For example on multiaccess

network that has multicast capabilities such as Ethernet it is not necessary to send hello packets

reliably to all neighbors individually For that reason EIGRP sends single multicast hello packet

containing an indicator that informs the receivers that the packet need not be acknowledged Other

types of packets such as updates indicate in the packet that acknowledgment is required RTP has

provision for sending multicast packets quickly when unacknowledged packets are pending which links helps ensure that convergence time remains low in the presence of varying speed

all tracks The DUAL finite state machine embodies the decision process for route computations It

all routes advertised by all neighbors DUAL uses distance information to select efficient loop-free

paths and selects routes for insertion in routing table based on feasible successors Afeasible

successor is neighboring router used for packet forwarding that is least-cost path to destination

which is guaranteed not to be part of routing loop When neighbor changes metric or when

topology change occurs DUAL tests for feasible successors If one is found DUAL uses it to avoid

recomputing the route unnecessarily When there are no feasible successors but there are neighbors

advertising the destination recomputation also known as diffusing computation must occur to

determine new successor Although recomputation is not processor intensive it does affect

convergence time so it is advantageous to avoid unnecessary recomputations

The protocol-dependent modules are responsible for network-layer protocol-specific requirements

For example the IP-EIGRP module is responsible for sending and receiving EIGRP packets that are

encapsulated in IP IP-EIGRP is also responsible for parsing EIGRP packets and informing DUAL

24-4 Internetworking Technology Overview EIGRP Technology

of the new information that has been received IP-EIGRP asks DUAL to make routing decisionsthe

results of which are stored in the IP routing table IP-EIGRP is responsible for redistributing routes

learned by other IP routing protocols

The consistent and superior performance of EIGRP relies on several new features

Packet types

Neighbor tables

Topology tables

Route states

Route tagging

Packet Types

EIGRP uses five packet types

Hello/acknowledgment

Update

Query

Request

An Hello packets are multicast for neighbor discovery/recovery and do not require acknowledgment contain acknowledgment packet is hello packet that has no data Acknowledgment packets

nonzero acknowledgment number and they are always sent using unicast address

Update packets are used to convey reachability of destinations When new neighbor is discovered

unicast update packets are sent so the neighbor can build up its topology table In other cases such

as link cost change updates are multicast Updates are always transmitted reliably

Query and reply packets are sent when destination has no feasible successors Query packets are

in to indicate to the always multicast Reply packets are sent response to query packets originator that the originator does not need to recompute the route because there are feasible successors Reply Both and transmitted packets are unicast to the originator of the query query reply packets are

reliably

Request packets are used to get specific information from one or more neighbors Request packets unicast transmitted are used in route server applications and can be multicast or Request packets are

unreliably

Neighbor Tabes

address and interface When router discovers new neighbor it records the neighbors as an entry module When in the neighbor table There is one neighbor table for each protocol-dependent

the of time router treats neighbor sends hello packet it advertises hold time which is amount received within the hold hold neighbor as reachable and operational If hello packet isnt timethe

time expires and DUAL is informed of the topology change

numbers The neighbor table entry also includes information required by RTP Sequence are number received from employed to match acknowledgments with data packets The last sequence

transmission list is used the neighbor is recorded so out-of-order packets can be detected to queue

timers in the packets for possible retransmission on per-neighbor basis Round-trip are kept retransmission interval neighbor table entry to estimate an optimal

Protocol 24-5 Interior Gateway Routing Protocol and Enhanced Interior Gateway Routing EIGRP Technology

Topology Tables

The topology table contains all destinations advertised by neighboring routers The protocol-

dependent modules populate the table and the table is acted on by the DUAL finite state machine

Each entry in the topology table includes the destination address and list of neighbors that have advertised the destination For each neighbor the entry records the advertised metric which the

in neighbor stores its routing table An important rule that distance vector protocols must follow is

that if the neighbor is advertising this destination it must be using the route to forward packets

The metric that the router uses to reach the destination is also associated with the destination The

metric that the router uses in the routing table and to advertise to other routers is the sum of the best

advertised metric from all neighbors plus the link cost to the best neighbor

Route States

topology table entry for destination can be in one of two states active or passive destination

is in the passive state when the router is not performing recomputation or in the active state when

the router is performing recomputation If feasible successors are always available destination

never has to go into the active state thereby avoiding recomputation

recomputation occurs when destination has no feasible successors The router initiates the

recomputation by sending query packet to each of its neighboring routers The neighboring router

can send reply packet indicating it has feasible successor for the destination or it can send

query packet indicating that it is participating in the recomputation While destination is in the

active state router cannot change the destinations routing table information Once the router has received reply from each neighboring router the topology table entry for the destination returns to

the passive state and the router can select successor

Route Tagging

EIGRP supports internal and external routes Internal routes originate within an EIGRP AS

Therefore directly attached network that is configured to run EIGRP is considered an internal

route and is propagated with this information throughout the EIGRP AS External routes are learned

by another routing protocol or reside in the routing table as static routes These routes are tagged

individually with the identity of their origin

External routes are tagged with the following information

The router ID of the EIGRP router that redistributed the route

The AS number of the destination

configurable administrator tag

The ID of the external protocol

The metric from the external protocol

Bit flags for default routing

Route allows the network administrator tagging to customize routing and maintain flexible policy

controls Route tagging is particularly useful in transit ASs where EIGRP typically interacts with an

interdomain that routing protocol implements more global policies resulting in very scalable

policy-based routing

24-6 lnternetworking Technology Overview CH pTE 25

Open Shortest Path First

Background

Open Shortest Path First OSPF is routing protocol developed for Internet Protocol IF networks

by the interior gateway protocol IGP working group of the Internet Engineering Task Force IETF

in IGP based the shortest The working group was formed 1988 to design an on path first SPF

algorithm for use in the Internet large international network connecting research institutions

government agencies universities and private businesses Like the Interior Gateway Routing Protocol IGRP see Chapter 24 Interior Gateway Routing Protocol and Enhanced Interior

Gateway Routing Protocol for more information OSPF was created because the Routing unable Information Protocol RIP was in the mid-1980s increasingly to serve large heterogeneous Protocol for information RIP internetworks See Chapter 23 Routing Information more on

OSPF was derived from several research efforts including

Bolt Beranek and Newmans BBNs SPF algorithm developed in 1978 for the ARPANET

landmark packet-switching network developed in the early 1970s by BBN

Dr Perlmans research on fault-tolerant broadcasting of routing information 1988

BBNs work on area routing 1986

An early version of OSIs Intermediate System-to-Intermediate System IS-IS routing protocol

See Chapter 28 OSI Routing for more information on IS-IS

that it is in that As indicated by its acronym OSPF has two primary characteristics The first is open For its specification is in the public domain The OSPF specification is published as Request

second characteristic is that it is based on the SPF Comments RFC 1247 The principal algorithm

credited with its which is sometimes referred to as the Dijkstra algorithm named for the person

creation

Technoogy Bascs

advertisements OSPF is link state routing protocol As such it calls for the sending of link state within the hierarchical Information on attached interfaces LSA5 to all other routers same area

metrics used and other variables is included in OSPF LSAs As OSPF routers accumulate link state node information they use the SFF algorithm to calculate the shortest path to each

As link state algorithm OSPF contrasts with RIP and IGRP which are distance vector routing

their tables protocols Routers running the distance vector algorithm send all or portion of routing

in routing update messages but only to their neighbors

Open Shortest Path First 25-1 Routing Hierarchy

Routing Herarchy

Unlike RIP OSPF can operate within hierarchy The largest entity within the hierarchy is the

autonomous system AS An AS is collection of networks under common administration sharing

common routing strategy OSPF is an intra-AS interior gateway routing protocol although it is

capable of receiving routes from and sending routes to other ASs

An AS be divided into number of An is of can areas area group contiguous networks and

attached hosts Routers with multiple interfaces can participate in multiple areas These routers

which are called area border routers maintain separate topological databases for each area

topological database is essentially an overall picture of networks in relationship to routers The

topological database contains the collection of LSAs received from all routers in the same area

Because within the routers same area share the same information they have identical topological databases

The term domain is sometimes used to describe portion of the network in which all routers have

identical topological databases Domain is frequently used interchangeably with AS

An areas topology is invisible to entities outside the area By keeping area topologies separate

OSPF passes less routing traffic than it would if the AS were not partitioned

Area partitioning creates two different types of OSPF routing depending on whether the source and

destination are in the same or different areas Intra-area routing occurs when the source and

destination are in the same area interarea routing occurs when they are in different areas

An OSPF backbone is responsible for distributing routing information between areas It consists of

all area border routers networks not wholly contained in any area and their attached routers Figure 25-1 shows an example of an intemetwork with several areas

25-2 Internetworking Technology Overview Routing Hierarchy

Routérl

Router 11

Autonomous system

Figure 25-1 Hierarchical OSPF Internetwork

In this figure Routers 56 10 11 and 12 make up the backbone If host Hi in Area wishes to

send packet to host H2 in Area the packet is sent to Router 13 which forwards the packet to

Router 12 which sends the packet to Router ii Router ii forwards the packet along the backbone

to area border router Router 10 which sends the packet through two intra-area routers Router and

Router to be forwarded to host H2

The backbone itself is an OSPF area so all backbone routers use the same procedures and algorithms

to maintain routing information within the backbone that any area router would The backbone

topology is invisible to all intra-area routers as are individual area topologies to the backbone

Areas can be defined in such way that the backbone is not contiguous In this case backbone

connectivity must be restored through virtual links Virtual links are configured between any

backbone routers that share link to nonbackbone area and function as if they were direct links

AS border routers running OSPF learn about exterior routes through exterior gateway protocols Border Protocol EGPs such as Exterior Gateway Protocol EGP or Gateway BGP or through

configuration information See Chapter 26 Exterior Gateway Protocol and Chapter 27 Border

Gateway Protocol respectively for more information on these protocols

Open Shortest Path First 25-3 The SPF Algorithm

The SPF AHgorthm

The SPF routing algorithm is the basis for OSPF operations When an SPF router is powered up it

initializes its routing protocol data structures and then waits for indications from lower-layer

protocols that its interfaces are functional

Once router is assured that its interfaces are functioningit uses the OSPF Hello protocol to acquire

neighbors Neighbors are routers with interfaces to common network The router sends hello

packets to its neighbors and receives their hello packets In addition to helping acquire neighbors

hello packets also act as keepalives to let routers know that other routers are still functional

On multiaccess networks networks supporting more than two routers the Hello protocol elects

designated router and backup designated router The designated router is responsible among other

things for generating LSAs for the entire multiaccess network Designated routers allow reduction

in network traffic and in the size of the topological database

When the link state databases of two neighboring routers are synchronized the routers are said to be

adjacent On multiaccess networks the designated router determines which routers should become

adjacent Topological databases are synchronized between pairs of adjacent routers Adjacencies

control the distribution of routing protocol packets These packets are sent and received only on

adjacencies

Each router periodically sends an LSA LSAs are also sent when.a routers state changes LSAs

include information on routers adjacencies By comparing established adjacencies to link states

failed routers can be quickly detected and the networks topology altered appropriately From the

topological database generated from LSAs each router calculates shortest-path tree with itself as

root The shortest-path tree in turn yields routing table

Packet Format

All OSPF packets begin with 24-byte header as shown in Figure 25-2

Field length

in bytes Variable

Authent Version Packet Check- Type Router ID Area ID ication Authentication Data number length sum type

Figure 25-2 OSPF Header Format

The first field in the OSPF header is the OSPF version number The version number identifies the

particular OSPF implementation being used

Following the version number is the type field There are five OSPF packet types

Hello Sent at regular intervals to establish and maintain neighbor relationships

Database description Describes the contents of the topological database and are exchanged

when an adjacency is being initialized

Link state requestRequests pieces of neighbors topological database They are exchanged

after router has discovered through examination of database description packets that parts of

its topological database are out of date

25-4 Internetworking Technology Overview Additional OSPF Features

Link state updateResponses to link state request packets They are also used for the regular

dispersal of LSAs Several LSAs maybe included within single packet

Link state acknowledgmentAcknowledges link state update packets Link state update packets

must be explicitly acknowledged to ensure that link state flooding throughout an area is reliable process

Each LSA in link state update packet contains type field There are four LSA types

Router links advertisements RLAsDescribe the collected states of the routers links to

specific area router sends an RLA for each area to which it belongs RLAs are flooded

throughout the entire area and no further

Network links advertisements NLAsSent by the designated routers They describe all the

routers that are attached to .multiaccess network and are flooded throughout the area containing

the multiaccess network

Summary links advertisements SLAsSummarize routes to destinations outside an area but

within the AS They are generated by area border routers and are flooded throughout the area

Only intra-area routes are advertised into the backbone Both intra-area and interarea routes are

advertised into the other areas

AS external links advertisementsDescribe route to destination that is external to the AS AS

external links advertisements are originated by AS boundary routers This type of advertisement

is the only type that is forwarded everywhere in the AS all others are forwarded only within

specific areas

Following the OPSF packet headers type field is packet length field which provides the packets

length including the OSPF header in bytes

The router ID field identifies the packets source

The area ID field identifies the area to which the packet belongs All OSPF packets are associated

with single area

standard IP checksum field checks the entire packet contents for potential damage suffered in

transit

The authentication type field contains an authentication type Simple password is an example of

an authentication type All OSPF protocol exchanges are authenticated The authentication type is

configurable on per-area basis

The authentication field is 64 bits in length and contains authentication information

Additona OSPF Features

Additional OSPF features include equal-cost multipath routing and routing based on upper-layer

type of service TOS requests TOS-based routing supports those upper-layer protocols that can

specify particular types of service For example an application might specify that certain data is

urgent If OSPF has high-priority links at its disposal these can be used to transport the urgent datagram

OSPF supports one or more metrics If only one metric is used it is considered to be arbitrary and

lOS is not supported If more than one metric is used TOS is optionally supported through the use for each of the combinations of separate metric and therefore separate routing table eight

created by the three IP TOS bits the delay throughput and reliability bits For example if the IP

calculates routes to all TOS bits specify low delay low throughput and high reliability OSPF

destinations based on this TOS designation

Open Shortest Path First 25-5 Additional OSPF Features

IP subnet masks are included with each advertised destination enabling variable-length subnet

masks With variable-length subnet masks an IP network can be broken into many subnets of

various sizes This provides network administrators with extra network configuration flexibility

25-6 Internetworking Technology Overview 26

Exterior Gateway Protocol

Background

used in the The Exterior Gateway Protocol EGP is an interdomain reachability protocol Internet and large international network connecting research institutions government agencies universities

private commercial businesses EGP is documented in Request For Comments RFC 904 published

in April 1984

As the first exterior gateway protocol to gain widespread acceptance in the Internet EGP served

valuable purpose Unfortunately EGPs weaknesses have become more apparent as the Internet has grown and matured Because of these weaknesses EGP is currently being phased out of the Internet

and is being replaced by other exterior gateway protocols such as the Border Gateway Protocol

BGP and the Interdomain Routing Protocol IDRP For more information on these protocols see

Chapter 27 Border Gateway Protocol and Chapter 28 OSI Routing

Technoogy Bascs

EGP was originally designed to communicate reachability to and from the ARPANET core routers

in distinct administrative domains Information was passed from individual source nodes ntemet

which the information the called autonomous systems ASs up to the core routers passed through network within another This backbone until it could be passed down to the destination AS in 26-1 relationship between EGP and other ARPANET components is shown Figure

Core roUteu

Figure 26-1 EGP and the ARPANET

does metrics Although EGP is dynamic routing protocol it uses very simple design It not use contain network and therefore cannot make intelligent routing decisions EGP routing updates reachable reachability information In other words they specify that certain networks are through

certain routers

Exterior Gateway Protocol 26-1 Packet Format

EGP has three primary functions First routers running EGP establish set of neighbors These

neighbors are simply routers with which an EGP router wishes to share reachability information

there is no implication of geographic proximity Second EGP routers polls their neighbors to see if

they are alive Third EGP routers send update messages containing information about the

reachability of networks within their ASs

Packet Format

An EGP packet is shown in Figure 26-2

Field length in bytes Variable

EGP Autonomous Sequence version Type Code Status Checksum system Data number number number

Figure 26-2 EGP Packet Format

The first field in the EGP packet header is the EGP version number field This field identifies the

current EGP version and is checked by recipients to determine whether there is match between the

sender and recipient version numbers

field identifies the defines five shown in Table The type message type EGP separate message types 26-1

Table 26-1 EGP Message Types

Message Function

Neighbor acquisition Establishes/de-establishes neighbors

Neighbor reachability Determines if neighbors are alive

Poll Determines reachability of particular network

Routing update Provides routing updates

Error Indicates error conditions

The code field distinguishes among message subtypes

The status field contains message-dependent status information Status codes include insufficient

resources parameter problemprotocol violation and others

The checksum field is used to detect possible problems that may have developed with the packet in

transit

The autonomous system number field identifies the AS to which the sending router belongs

The sequence number field is the last field in the EGP packet header This field allows two EGP

routers exchanging messages to match requests with replies The sequence number is initialized to

zero when neighbor is established and incremented by one with each request-response transaction

26-2 Internetworking Technology Overview Message Types

Message Types

fields the Additional fields follow the EGP header The contents of these vary depending on message

type as specified by the type field

Neighbor Acquisition

field The hello The neighbor acquisition message includes hello interval field and poll interval

interval interval field specifies the interval period for testing whether neighbors are alive The p011

field specifies the routing update frequency

Neighbor Reachability

The neighbor reachability message adds no extra fields to the EGP header These messages use the code field to indicate whether the message is hello message or response to hello message

Separating the reachability assessment function from the routing update function reduces network

traffic because network reachability changes usually occur more often than routing parameter have been received does an changes Only after specified percentage of reachability messages not

EGP node declare neighbor to be down

Poll

relative location of remote hosts The To provide correct routing between ASs EGP must know the information about the networks which poll message allows EGP routers to acquire reachability on these hosts reside These messages only have one field beyond the common headerthe IP source

for the network field This field specifies the network to be used as reference point request

Ronting Update

locations of various Routing update messages provide way for EGP routers to indicate the include networks within their ASs In addition to the common header these messages many

of interior additional fields The number of interior gateways field indicates the number gateways number of exterior appearing in the message The number of exterior gateways field indicates the IP address of the gateways appearing in the message The IP source network field provides the of blocks network from which reachability is measured Following this field is series gateway and distances Each gateway block provides the IF address of gateway and list of networks

associated with reaching those networks

distance there Within the gateway block EGP lists networks by distances In other words at three of networks may be four networks These networks are then listed by address The next group may be those that are distance four away and so on

EGP does not interpret the distance metrics that are contained within the routing update messages distance value In essence EGP uses the distance field to indicate whether path exists the can only

if this EGP is be used to compare paths those paths exist wholly within particular AS For reason limitations more reachability protocol than routing protocol This restriction also places topology

be tree structure on the structure of the Internet Specifically an EGP portion of the Internet must within the This in which core gateway is the root and there are no loops among other ASs tree

restriction is primary limitation of EGP and provides an impetus for its gradual replacement by

other more capable exterior gateway protocols

Exterior Gateway Protocol 26-3 Message Types

Error

Error messages identify various EGP error conditions In addition to the common EGP header EGP

error messages provide reason field followed by an error message header Typical EGP errors

reasons include bad EGP header format bad EGP data field format excessive polling rate and

the unavailability of reachability information The error message header consists of the first three

32-bit words of the EGP header

26-4 lnternetworking Technology Overview CHAPTER 27

Border Gateway Protoco

Background

Exterior gateway protocols are designed to route between routing domains In the terminology of the

Internet large international network connecting research institutions government agencies

universities and private businesses routing domain is called an autonomous system AS .The first

exterior gateway protocol to achieve widespread acceptance in the Internet was the Exterior

Gateway Protocol EGP See Chapter 26 Exterior Gateway Protocol for more information on

EGP Although EGP is useful technology it has several weaknesses including the fact that it is

more reachability protocol than routing protocol

The Border Gateway Protocol BGP represents an attempt to address the most serious of EGPs

problems BGP is an inter-AS routing protocol created for use in the Internet Unlike EGP BGP was

designed to detect routing loops BGP may be thought of as next-generation EGP Indeed BGP and

other inter-AS routing protocols are slowly replacing EGP in the Internet BGP Version is

specified in Request For Comments RFC 1163

To address the needs of the growing Internet BGP continues to evolve future version of BGP will

give it the ability to aggregate or summarize groups of similar routes into one route

TechnoHogy Bascs

within and between Although BGP was designed as an inter-AS protocol it can be used both ASs

Two BGP neighbors communicating between ASs must reside on the same physical network BGP

routers within the same AS communicate with one another to ensure that they have consistent view

of the AS and to determine which BGP router within that AS will serve as the connection point to or

from certain external ASs

Some ASs are merely pass-through channels for network traffic In other words some ASs carry with network traffic that did not originate within and is not destined for them BGP must interact

whatever intra-AS routing protocols exist within these pass-through ASs

BGP update messages consist of network number/AS path pairs The AS path contains the string of the ASs through which the specified network may be reached These update messages are sent over

Transmission Control Protocol transport mechanism to ensure reliable delivery

The initial data exchange between two routers is the entire BGP routing table Incremental updates

are sent out as the routing tables change Unlike some other routing protocols BGP does not require

periodic refresh of the entire routing table Instead routers running BGP retain the latest version of

each table maintains table with all feasible to peer routing Although BGP routing paths particular

network it only advertises the primary optimal path in its update messages

Border Gateway Protocol 27-1 Packet Format

The BGP metric is an arbitrary unit number specifying the degree of preference of particular path

These metrics are typically assigned by the network administrator through configuration files

Degree 91 preference may be based on any number of criteria including AS count paths with smaller AS link link stable fast count are generally better type of is the reliable and other factors

Packet Format

The BGP packet format is shown in Figure 27-1

Held length

in bytes

Figure 27-1 BGP Packet Format

BGP packets have common 19-byte header consisting of three fields

The marker field is 16 bytes long and contains value that the receiver of the message can

predict.This field is used for authentication

The length field contains the total length of the message in bytes

The field the type specifies message type

Messages

Four message types are specified in RFC 1163

Open

Update

Notification

Keepalive

Open

After transport protocol connection is established the first message sent by each side is an open

message If the open message is acceptable to the recipient keepalive message confirming the open message is sent back Upon successful confirmation of the open message updates keepalives and notifications may be exchanged

In addition to the common BGP packet header open messages define several fields The version field

provides BGP version number and allows the recipient to check that it is running the same version the sender as The autonomous system field provides the AS number of the sender The hold-time

field indicates the maximum number of seconds that may elapse without receipt of message before

the transmitter is assumed to be dead The authentication code field indicates the authentication type being used if any The authentication data field contains actual authentication data if any

27-2 Internetworking Technology Overview Messages

Update

BGP update messages provide routing updates to other BGP systems Information in these messages

is used to construct graph describing the relationships of the various ASs In addition to the

common BGP header update messages have several additional fields These fields provide routing

information by listing path attributes corresponding to each network

BGP currently defines five attributes

OriginCan take on one of three values IGP EGP and incomplete The TOP attribute means

that the network is part of the AS The EGP attribute means that the information was originally

learned from the EGP BGP implementations would be inclined to prefer IGP routes over EGP

fails The attribute is used routes since EGP in the presence of routing loops incomplete to

indicate that the network is known via some other means

AS pathProvides the actual list of ASs on the path to the destination

Next hopProvides the IP address of the router that should be used as the next hop to the

networks listed in the update message

UnreachableIf present indicates that route is no longer reachable

Inter-AS metricProvides way for BOP router to advertise its cost to destinations within its

own AS This information can be used by routers external to the advertisers AS to select an

optimal route into the AS to particular destination

Notificaton

Notification messages are sent when an error condition has been detected and one router wishes to

tell another why it is closing the connection between them Aside from the common BGP header

notification messages have an error code field an error subcode field and error data The error code

field indicates the type of error and can be one of the following

Message header errorIndicates problem with the message header such as an unacceptable

message length an unacceptable marker field value or an unacceptable message type

Open message errorIndicates problem with an open message such as an unsupported version

number an unacceptable AS number or IP address or an unsupported authentication code

Update message errorIndicates problem with the update message Examples include

malformed attribute list an attribute list error and an invalid next-hop attribute

Hold time expiredIndicates hold-time expiration after which BGP node will be declared dead

KeepaUive

in the header Keepalive messages do not contain any additional fields beyond those common BGP These messages are sent often enough to keep the hold-time timer from expiring

Border Gateway Protocol 27-3 Messages

21-4 Internetworking Technology Overview 28

OS Routing

Background

Several routing protocols have been or are being developed under the auspices of the International

Organization for Standardization ISO ISO refers to the Intermediate System to Intermediate National System Intradomain Routing Exchange Protocol IS-IS as ISO 10589 The American

Standards Institute ANSI X3S3 .3 network and transport layers committee was the motivating

force behind ISO standardization of IS-IS Other ISO protocols associated with routing include ISO

9542 End System-to-Intermediate System or ES-IS and ISO 10747 IS-IS Interdomain Routing

Protocol or IDRP Both of these protocols are discussed briefly in this chapter but the focus is on

the intradomain version of IS-IS

IS-IS is based on work originally done at Digital Equipment Corporation for Phase DECnet

Although IS-IS was created to route in ISO Connectionless Network Protocol CLNP networks

version has since been created to support both CLNP and Internet Protocol IF networks This

variety of IS-IS is usually referred to as Integrated IS-IS and has also been called Dual IS-IS

Integrated IS-IS is also discussed briefly

Term no gy

The world of OSI internetworking has unique terminology The term end system ES refers to any

nonrouting network node the term intermediate system IS refers to router These terms are the

basis for the OSI protocols ES-IS which allows ESs and ISs to discover each other and IS-IS which

provides routing between ISs Several other important OSI internetworking terms are defined as

follows

and attached hosts that to be AreaA group of contiguous networks are specified an area by

network administrator or manager

Domain collection of connected areas Routing domains provide full connectivity to all end

systems within them

Level routingRouting within level area

Level routingRouting between level areas

Figure 28-1 shows the relationship between these terms

OSI Routing 28-1 ES-IS

Domain

Figure 28-1 Hierarchies in OSI Internetworks

From purely technological standpoint IS-IS is quite similar to the Open Shortest Path First

OSPF routing protocol see Chapter 25 Open Shortest Path First for more information on of the OSPF Both are link state protocols Both offer variety f7eatures not provided by Routing Information Protocol RIP including routing hierarchiespath splitting type-of-service TOS

support authentication support for multiple network-layer protocols and with Integrated IS-IS

support for variable length subnet masks

ESiS

ES-IS is more discovery protocol than routing protocol Through ES-IS ESs and ISs learn about

each other This process is known as configuration And because configuration must happen before

routing between ESs can occur ES-IS is discussed here

ES-IS distinguishes between three different types of subnetworks

Point-to-point subnet-worksProvide point-to-point link between two systems Many wide-

area network WAN serial links are point-to-point networks

Broadcast subnetworksDirect single physical message to all nodes on the subnetwork

Ethernet and IEEE 802.3 are examples of broadcast subnetworks For more information about

Ethernet and IEEE 802.3 see Chapter Ethernet/IEEE 802.3

General-topology subnetworks Support an arbitrary number of systems However unlike

broadcast subnetworks the cost of an n-way transmission scales directly with the subnetwork

size on general-topology subnetwork X.25 is an example of general-topology subnetwork

For more information about X.25 see Chapter 12 X.25

Configuration information is transmitted at regular intervals through two types of messages ES hello

messages ESHs are generated by ESs and sent to every IS on the subnetwork IS hello messages

ISHs are generated by ISs and sent to all ESs on the subnetwork These hello messages are

primarily intended to convey the subnetwork and network-layer addresses of the systems that

generate them

28-2 Internetworking Technology Overview Is-Is

information Where possible ES-IS attempts to send configuration to many systems simultaneously

all ISs multicast On broadcast subnetworks ES-IS hello messages are sent to through special address ISs send hello messages to special multicast address designating all end systems When does transmit operating on general-topology subnetwork ES-IS generally not configuration

information because of the high cost of multicast transmissions

OSI ES-IS conveys both network-layer addresses and subnetwork addresses network-layer

addresses either the service which is the interface between identify network access point NSAP

and the title is the in an OSI IS layer layer or network entity NET which network layer entity

OSI subnetwork addresses sometimes called subneiwork point of attachment addresses or SNPAs address are the points at which an ES or IS is physically attached to subnetwork The SNPA the uniquely identifies each system attached to the subnetwork In an Ethernet network for example information SNPA is the 48-bit Media Access Control MAC address Part of the configuration transmitted by ES-IS is the NSAP-to-SNPA or NET-to-SNPA mapping

Figure 28-2 shows the frame formats of both ESH and ISH packets

ESH

Field length in bytes bits Variable

Network Version Number of Source Source layer Length protocol Type of Holding Check- Reserved source address addresses protocol indicator ID packet time sum addresses length identifier extensions

May be

ISH repeated

Field length Variable in bytes bits

Network Version

layer Length protocol Type of Holding Check- Net Reserved NET protocol indicator ID packet time sum length

identifier extensions

Figure 28-2 ESH and ISH Packet Formats

s.is

IS-IS is link state routing protocol It floods the network with link state information in order to

build complete consistent picture of network topology

Routing Hierarchy

between level and level ISs Level To simplify router design and operation IS-IS distinguishes

ISs know how to communicate with other level ISs in the same area Level ISs know how to

communicate with ISs in other areas To summarize level lISs form level areas level ISs route

between level areas

Level 2ISs form an intradomain routing backbone In other words level ISs can get to other level

because level ISs now need ISs by traversing only level ISs The backbone simplifies design only

can also without to know how to get to the nearest level 21S The backbone routing protocol change

impacting the intra-area routing protocol

OSI Routing 28-3 Is-Is

kiter-ES Communication

OSI routing is accomplished as follows Each ES lives in particular area ESs discover the nearest

IS by listening to ISH packets When an ES wants to send packet to another ES it sends the packet

to one of the ISs on its directly attached network The router looks up the destination address and

forwards the packet along the best route If the destination ES is on the same subnetwork the local

IS will know this from listening to ESHs and will forward the packet appropriately In this case the

IS may also provide redirect RD message back to the source to tell it that more direct route is

available If the destination address is an ES on another subnetwork in the same area the IS will

know the correct route and will forward the packet appropriately If the destination address is an ES

in another area the level IS sends the packet to the nearest level IS Forwarding through level

ISs continues until the packet reaches level IS in the destination area Within the destination area

ISs forward the packet along the best path until the destination ES is reached

and which it is well the Each IS generates an update specifying the ESs ISs to connected as as

associated metrics The update is sent to all neighboring ISs which forward flood it to their

neighbors and so on sequence numbers terminate the flood and distinguish old updates from new

ones Because all ISs receive link state updates from all other ISs each IS can build complete full

topology database When the topology changes new updates are sent

Metrics

The metric is IS-IS uses single required default metric with maximum path value of 1024

link have maximum arbitrary and is typically assigned by network administrator Any single can metric values value of 64 Path lengths are calculated by summing link values Maximum were set time at these levels to provide the granularity to support various link types while at the same

ensuring that the shortest path algorithm used for route computation would be reasonably efficient

IS-IS also defines three additional metrics costs as an option for those administrators who feel they

The reflects the of the link The cost reflects the are necessary delay cost amount delay on expense

communications cost associated with using the link The error cost reflects the error rate of the link

IS-IS maintains mapping of these four metrics to the quality of service QOS option in the CLNP

packet header Using these mappings IS-IS can compute routes through the internetwork

Packet Format

Is-IS uses three basic packet formats

IS-IS hello packets

Link state packets LSPs

Sequence numbers packets SNPs

Each of the three IS-IS packets has complex format with three different logical parts The first part

is an eight-byte fixed header shared by all three packet types The second part is packet-type-

specific portion with fixed format The third logical part is also packet-type-specific but is of

variable length The logical format of IS-IS packets is shown in Figure 28-3

Packet-type- Packet-type-

Common header specific specific variable-

fixed header length header ______

Figure 28-3 IS-IS Logical Packet Format

28-4 Internetworking Technology Overview Integrated IS-IS

Each of the three packet types shares common header as shown in Figure 28-4

Field length

mbytes

Figure 28-4 IS-IS Common Header Format

The first field in the IS-IS common header is the protocol identfler which identifies the IS-IS

protocol This field contains constant 131

The header length field contains the fixed header length The length is always equal to eight bytes

but is included so that IS-IS packets wont differ significantly from CLNP packets

The version field is equal to one in the current IS-IS specification

The ID length field specifies the size of the ID portion of an NSAP if between one and eight

inclusive If the field contains zero the ID portion equals six bytes If the field contains 255 all

ones the ID portion is zero bytes

field the of IS-IS The packet type specifies type packet hello LSP or SNP

The version field is repeated after the packet type field

The reserved field is equal to zero and is ignored by the receiver

The maximum area addresses field specifies the number of addresses permitted in this area

Following the common header each packet type has different additional fixed portion followed

by variable portion

ntegrated SIS

Integrated IS-IS is version of IS-IS that uses single routing algorithm to support more network-

layer protocols than just CLNP Integrated IS-IS is sometimes called Dual IS-IS after version

designed for IP and CLNP networks

Several fields are added to IS-IS packets to allow IS-IS to support additional network layers These

fields inform routers about

The reachability of network addresses from other protocol suites

Which protocols are supported by which routers

Other information required by specific protocol suite

network in Integrated IS-IS represents one of two ways of supporting multiple layer protocols

router the other being the ships-in-the-night approach Ships-in-the-night advocates the use of

that the completely separate and distinct routing protocol for each network protocol so multiple

routing protocols essentially exist independently with different types of routing information passing

tables like ships in the night The ability to route multiple network-layer protocols through

calculated by single routing protocol saves some router resources

OSI Routing 28-5 Interdomain Routing Protocol IDUP

nterdoman Routng Protoc DRP

domains As it is IDRP is the OSI protocol designed to move information between routing such

and IS-IS IDRP is based on the Border designed to operate seamlessly with CLNP ES-IS Gateway Protocol BGP an interdomain routing protocol that originated in the IP community For more information on BGP see Chapter 27 Border Gateway Protocol

IDRP introduces several new terms including

in interdomain As such it Border intermediate system BISAn IS that participates routing

uses IDRP

under the set of administrative Routing domain RDA group of ESs and ISs operating same

rules including the sharing of common routing plan

identifier Routing domain identUler RDIA unique RD

used IDRP RIBs built each Routing information base RIBThe routing database by are by

BIS from information received from within the RD and from other BISs RIB contains the set

of routes chosen for use by particular BIS

The confederation to RDs outside the confederation as Confederation group of RDs appears the confederation single RD confederations topology is not visible to RDs outside and be Confederations help reduce network traffic by acting as intemetwork firewalls may

nested within one another

of these RDIs can be confederations Each BIS is An IDRP route is sequence of RDIs Some about other configured to know the RD and confederations to which it belongs and learns BISs with distance RDs and confederations through information exchanges with each neighbor As vector that routing routes to particular destination accumulate outward from the destination Only routes

satisfy BISs local policies and have been selected for use will be passed on to other BISs Route

recalculation is partial and occurs when one of three events occurs an incremental routing update

with new routes is received BIS neighbor goes down or BIS neighbor comes up

IDRP features include

Support for CLNP QOS

traversed route Loop suppression by keeping track of all RDs by

Reduction of route information and processing by using confederations the compression of RD

path information and other means

Reliability by using built-in reliable transport

basis Security by using cryptographic signatures on per-packet

Route servers

RIB refresh packets

2U-6 Internetworking Technology Overview

CHAPTER 29

Transparent Bridging

Background

Transparent bridges were first developed at Digital Equipment Corporation Digital in the early

Electrical and Electronic 1980s Digital submitted its work to the Institute of Engineers IEEE

which incorporated the work into the IEEE 802.1 standard Transparent bridges are very popular in

Ethernet/IEEE 802.3 networks

Technoogy Basics

network Transparent bridges are so named because their presence and operation are transparent to

the hosts When transparent bridges are powered on they learn the networks topology by analyzing

source address of incoming frames from all attached networks If for example bridge sees frame

arrive on line from Host the bridge concludes that Host can be reached through the network

in connected to line Through this process transparent bridges build table such as the one

Figure 29-1

Host address Network number

Figure 29-1 Transparent Bridging Table

The bridge uses its table as the basis for traffic forwarding When frame is received on one of the

bridges inteacesthe bridge looks up the frames destination address in its internal table If the table

contains an association between the destination address and any of the bridges ports aside from the

one on which the frame was received the frame is forwarded out the indicated port If no association

is found the frame is flooded to all ports except the inbound port Broadcasts and multicasts are also flooded in this way

Transparent Bridging 29-1 Bridging Loops

Transparent bridges successfully isolate intrasegment traffic thereby reducing the traffic seen on individual each segment This usually improves network response times as seen by the user The

extent to which traffic is reduced and response times are improved depends on the volume of

intersegment traffic relative to the total traffic as well as the volume of broadcast and multicast

traffic

Bridgng Loops

Without bridge-to-bridge protocol the transparent bridge algorithm fails when there are multiple

paths of bridges and local-area networks LAN5 between any two LANs in the intemetwork

Figure 29-2 illustrates such bridging ioop

Network

Figure 29-2 Inaccurate Forwarding and Learning in Transparent Bridging Environments

Suppose Host sends frame to Host Both bridges receive the frame and correctly conclude that

Host is on Network Unfortunately after Host receives two copies of Host As frame both

bridges will again receive the frame on their Network interfaces because all hosts receive all

messages on broadcast LANs In some cases the bridges will then change their internal tables to indicate that Host is on Network If so when Host replies to Host As frame both bridges will

receive and subsequently drop the replies since their tables will indicate that the destination Host

is on the same network segment as the frames source

In addition to basic connectivity problems such as the one just described the proliferation of

broadcast messages in networks with loops represents potentially serious network problem

Referring again to Figure 29-2 assume that Host As initial frame is broadcast Both bridges will

forward the frames endlessly using all available network bandwidth and blocking the transmission

of other packets on both segments

topology with loops such as that shown in Figure 29-2 can be useful as well as potentially harmful

loop implies the existence of multiple paths through the internetwork network with multiple

paths from source to destination can increase overall network fault tolerance through improved

topological flexibility

29-2 Internetworking Technology Overview Spanning-Tree Algorithm STA

Spanning-Tree Agodthm STA

The Ethernet spanning-tree algorithm STA was developed by Digital key vendor to preserve the

benefits of loops while eliminating their problems Digitals algorithm was subsequently revised by

the IEEE 802 committee and published in the IEEE 802.ld specification The Digital algorithm and

the IEEE 802.ld algorithm are not the same nor are they compatible

The STA subset of the designates loop-free networks topology by placing those bridge ports that

if would into active create loops standby blocking condition Blocking bridge ports can be

activated in the event of primary link failure providing new path through the internetwork

The STA uses conclusion from graph theory as basis for constructing loop-free subset of the

networks topology Graph theory states the following

For any connected graph consisting of nodes and edges connecting pairs of nodes there is

spanning tree of edges that maintains the connectivity of the graph but contains no loops

Figure 29-3 illustrates how the STA eliminates ioops The STA calls for each bridge to be assigned

unique identifier Typically this identifier is one of the bridges Media Access Control MAC

addresses plus priority Each port in every bridge is also assigned unique within that bridge

identifier typically its own MAC address Finally each bridge port is associated with path cost

The path cost represents the cost of transmitting frame onto LAN through that port In

Figure 29-3 path costs are noted on the lines emanating from each bridge Path costs are usually

defaulted but can be assigned manually by network administrators

Designated port Root port

through LANs

Figure 29-3 Transparent Bridge Network Before Running STA

The first activity in spanning-tree computation is the selection of the root bridgewhich is the bridge

with the lowest value bridge identifier In Figure 29-3the root bridge is Bridge Next the root port

all other on bridges is determined bridges root port is the port through which the root bridge may

be reached with the least aggregate path cost This value the least aggregate path cost to the root is

called the root path cost

Finally designated bridges and their designated ports are determined designated bridge is the

bridge on each LAN that provides the minimum root path cost LANs designated bridge is the

only bridge allowed to forward frames to and from the LAN for which it is the designated bridge

LANs designated port is that port which connects it to the designated bridge

Transparent Bridging 29-3 Frame Format

In some cases two or more bridges may have the same root path cost For example in Figure 29-3

Bridges and can both reach Bridge the root bridge with path cost of 10 In this case the

bridge identifiers are used again this time to determine the designated bridges Bridge 4s LAN

port is selected over Bridge Ss LAN port

connected to each Using this process all but one of the bridges directly LAN are eliminated thereby

removing all two-LAN loops The STA also eliminates loops involving more than two LANs while

still preserving connectivity Figure 29-4 shows the results of applying the STA to the network

shown in Figure 29-3 Figure 29-4 shows the tree topology more clearly Comparing this figure to

the pre-spanning-tree figure shows that the STAhas placed both Bridge 3s and Bridge 5s ports to

LAN in standby mode

Active port

Blocking port

Figure 29-4 Transparent Bridge Network After Running STA

The spanning-tree calculation occurs when the bridge is powered up and whenever topology

change is detected The calculation requires communication between the spanning-tree bridges

which is effected through configuration messages sometimes called bridge protocol data units or

BPDUs Configuration messages contain information identifying the bridge that is presumed to be

the root root identifier and the distance from the sending bridge to the root bridge root path cost

Configuration messages also contain the bridge and port identifier of the sending bridge and the age of information contained in the configuration message

Bridges exchange configuration messages at regular intervals typically one to four seconds If

bridge fails causing topology change neighboring bridges will soon detect the lack of

configuration messages and initiate spanning-tree recalculation

All transparent bridge topology decisions are made locally Configuration messages are exchanged

between neighboring bridges There is no central authority on network topology or administration

Frame Format

Transparent bridges exchange configuration messages and topology change messages

Configuration messages are sent between bridges to establish network topology Topology change

messages are sent after topology change has been detected to indicate that the STA should be rerun

The transparent bridge configuration message format is shown in Figure 29-5

29-4 Internetworking Technology Overview Frame Format

Field length in bytes

Protocol Message Message Maximum Hello Forward Version Flags Root ID path Bridge ID Po ID identifier type age age time delay cost

Figure 29-5 Transparent Bridge Configuration Message Format

The protocol identifier field contains the value zero

The version field contains the value zero

The message type field contains the value zero

Theflags field is one-byte field of which only the first two bits are used The topology change TC

bit signals topology change The topology change acknowledgment TCA bit is set to acknowledge receipt of configuration message with the IC bit set

The root ID field identifies the root bridge by listing its two-byte priority followed by its six-byte ID

The root path cost field contains the cost of the path from the bridge sending the configuration

message to the root bridge

The bridge ID field identifies the priority and ID of the bridge sending the message

The port ID field identifies the port from which the configuration message was sent This field allows

loops created by multiply attached bridges to be detected and dealt with

The message age field specifies the amount of time since the root sent the configuration message on

which the current configuration message is based

The maximum age field indicates when the current configuration message should be deleted

The hello time field provides the time period between root bridge configuration messages

The forward delay field provides the length of time that bridges should wait before transitioning to

new state after topology change If bridge transitions too soon not all network links may be

ready to change their state and ioops can result

Topological change messages consist of only four bytes They include protocol identijier field

which contains the value zero version field which contains the value zero and message type

field which contains the value 128

Transparent Bridging 29-5 Frame Format

29-6 Internetworking Technology Overview CHAPTER 30

SourceRoute Bridging

Background

The source-route bridging SRB algorithm was developed by IBM and proposed to the IEEE 802.1

committee as the means to bridge between all local-area networks LANs The IEEE 802.1

committee selected competing standard see Chapter 29 Transparent Bridging for more

information on the transparent bridging standard SRB supporters proposed SRB to the IEEE 8025

committee which subsequently adopted SRB into the IEEE 802.5 Token Ring LAN specification

Since its initial proposal IBM has offered new bridging standard to the IEEE 802 committee the

source-route transparent SRT bridging solution See Chapter 31 Mixed-Media Bridging for information more on SRT bridging SRT bridging eliminates pure SRBs entirely proposing that the

two types of LAN bridges be transparent bridges and SRT bridges Although SRT bridging has

achieved support SRBs are still widely deployed

SRB APgorthm

SRBs are so named because they assume that the complete source-to-destination route is placed in

all inter-LAN frames sent by the source SRBs store and forward the frames as indicated by the route appearing in the appropriate frame field Figure 30-1 illustrates sample SRB network

Source-Route Bridging 30-1 SRI3 Algorithm

Figure 30-1 Sample SRB Network

wishes send frame to Host Host does Referring to Figure 30-1 assume that Host to Initially sends not know whether Host resides on the same or different LAN To determine this Host has out test frame If that frame returns to Host without positive indication that Host seen it

Host must assume that Host is on remote segment

To determine the exact remote location of Host Host sends an explorer frame Each bridge

the frame onto all outbound receiving the explorer frame Bridges and in this example copies

information is added to the frames as travel through the internetwork ports Route explorer they each the When Host Xs explorer frames reach Host Host replies to individually using Host choose accumulated route information Upon receipt of all response frames may path

based on some predetermined criteria

this will two routes In the example in Figure 30-1 process yield

LAN Bridge LAN Bridge LAN

does mandate the Host must select one of these two routes The IEEE 802.5 specification not

the criteria Host should use in choosing route but it does make several suggestions including

following

First frame received

Response with the minimum number of hops

size Response with the largest allowed frame

Various combinations of the above criteria

received will be used In most cases the path contained in the first frame

30-2 Internetworking Technology Overview Frame Format

After route is selected it is inserted into frames destined for Host Yin the form of routing

RIF is included in those frames destined for other LANs The information field RIF only of the presence of routing information within the frame is indicated by the setting most significant bit bit within the source address field called the routing information indicator Ru

Frame Format

The IEEE 802.5 R1F is structured as shown in Figure 30-2

802.5 MAC frame

// 7/ 7/7/ .7

Ring Bridge Not used TYPe Length Largest number number

Figure 30-2 IEEE 802.5 RIF

routed The type subfield in the RIP indicates whether the frame should be to single node group

The first is called of nodes that make up spanning tree of the intemetwork or all nodes type

and the third is specifically routed frame the second type is called spanning-tree explorer type

transit mechanism for called an all-paths explorer The spanning-tree explorer can be used as

in outbound multicast frames It can also be used as replacement for the all-paths explorer route

queries In this case the destination responds with an all-paths explorer

The length subfield indicates the total length in bytes of the RIP

The bit indicates the direction of the frame forward or reverse

The largest field indicates the largest frame that can be handled along this route

number that There can be multiple route descriptor fields Each carries ring number-bridge pair of LAN and specifies portion of route Routes then are simply alternating sequences bridge

numbers that start and end with LAN numbers

Source-Route Bridging 30-3 Frame Format

30-4 Internetworking Technology Overview CHAPTER 31

MixedMedia Bridging

Background

Transparent bridges are found predominantly in Ethernet networks and source-route bridges

SRBs are found almost exclusively in Token Ring networks See Chapter 29 Transparent

Bridging for more information on transparent bridges see Chapter 30 Source-Route Bridging

for more information on SRBs Both transparent bridges and SRBs are popular so it is reasonable to

ask whether method exists to bridge between them This basic question is illustrated in Figure 31-1

Transparent

bridge Transparent .-

bridge

______p

Transparent

bridge

SRB bridge environment TB bridge environment

Figure 31-1 Bridging Between Transparent Bridging and SRB Domains

Technoogy Basics

Translational bridging provides relatively inexpensive solution to some of the many problems

involved with bridging between transparent bridging and SRB domains Translational bridging first

appeared in the mid- to late-1980s but has not been championed by any standards organization As

result many aspects of translational bridging are left to the implementor

Mixed-Media Bridging 31-1 Technology Basics

In 1990 IBM addressed some of the weaknesses of translational bridging by introducing source-

route transparent SRT bridging SRT bridges can forward traffic from both transparent and source-

route end nodes and form common spanning tree with transparent bridges thereby allowing end

stations of each type to communicate with end stations of the same type in network of arbitrary

topology

Ultimately the goal of connecting transparent bridging and SRB domains is to allow communication

between transparent bridges and SRB end stations This chapter describes the technical problems

that be addressed must by algorithms attempting to do this and presents two possible solutions

translational bridging and SRT bridging

TrausIaton Chaflenges

There are number of challenges associated with allowing end stations from the Ethernet

transparent bridging domain to communicate with end stations from the SRB/Token Ring domain

including the following

Incompatible bit orderingAlthough both Ethernet and Token Ring support 48-bit Media

Access Control MAC addresses the internal hardware representation of these addresses differs

In serial bit stream representing an address Token Ring considers the first bit encountered to

be the high-order bit of byte Ethernet on the other hand considers the first bit encountered to

be the low-order bit

Embedded MAC addressesIn some cases MAC addresses are actually carried in the data

portion of frame For example the Address Resolution Protocol ARP popular protocol in

Transmission Control Protocol/Internet Protocol TCP/IP networks places hardware addresses

in the data of frame Conversion of addresses that in portion link-layer may or may not appear

the data portion of frame is difficult because they must be handled on case-by-case basis

Incompatible maximum transfer unit MTU sizesToken Ring and Ethernet support different

maximum frame sizes Ethernets MTU is approximately 1500 bytes whereas Token Ring

frames can be much larger As bridges are not capable of frame fragmentation and reassembly

packets that exceed the MTU of given network must be dropped

Handling of frame status bit actions Token Ring frames include three frame status bits

and The of these bits is tell purpose to the frames source whether the destination saw the frame

bit setcopied the frame bit set and/or found errors in the frame bit set Since Ethernet

does not support these bits the question of how to deal with them is left to the Ethernet-Token

Ring bridge manufacturer

Handling of exclusive Token Ring functionsCertain Token Ring bits have no corollary in

Ethernet For example Ethernet has no priority mechanism whereas Token Ring does Other

Token Ring bits that must be thrown out when Token Ring frame is converted to an Ethernet

frame include the token bit the monitor bit and the reservation bits

Handling of explorer framesTransparent bridges do not inherently understand what to do with

SRB explorer frames Transparent bridges learn about the networks topology through analysis

of the source address of incoming frames They have no knowledge of the SRB route discovery

process

Handling of routing information field RIF information within Token Ring frames The SRB

algorithm places routing information in the RIF field The transparent bridging algorithm has no

R1F equivalent and the idea of placing routing information in frame is foreign to transparent

bridging

31-2 Internetworking Technology Overview Translational Bridging

Incompatible spanning-tree algorithms Transparent bridging and SRB both use the spanning-

tree algorithm to try to avoid loops but the particular algorithms employed by the two bridging

methods are incompatible

Handling of frames without route information SRBs expect all inter-LAN frames to contain

route information When frame without RIF field including transparent bridging

configuration and topology change messages as well as MAC frames sent from the transparent

bridging domain arrives at an SRB bridge it is simply ignored

Transatonai Brdgng

Because there has been real in no standardization how communication between two media types

should occur there is no single translational bridging implementation that can be called correct The

following describes several popular methods for implementing translational bridging

Translational bridges reorder source and destination address bits when translating between Ethernet

and Token Ring frame formats The problem of embedded MAC addresses can be solved by

programming the bridge to check for various types of MAC addresses but this solution must be with adapted each new type of embedded MAC address Some translational bridging solutions

simply check for the most popular embedded addresses If translational bridging software runs in

multiprotocol router the router can successfully route these protocols and avoid the problem

entirely

The RIF field has subfield that indicates the largest frame size that can be accepted by particular

SRB implementation Translational bridges that send frames from the transparent bridging domain

to the SRB domain usually set the MTU size field to 1500 bytes to limit the size of Token Ring

frames entering the transparent bridging domain Some hosts cannot correctly process this field in

which case translational bridges are forced to simply drop those frames that exceed Ethernets MTU size

Bits representing Token Ring functions that have no Ethernet corollary are typically thrown out by

translational bridges For example Token Rings priority reservation and monitor bits contained

in the access-control byte are discarded Token Rings frame status bits contained in the byte

following the ending delimiter which follows the data field are treated differently depending on the

translational bridge manufacturer Some translational bridge manufacturers simply ignore the bits

Others have the bridge set the bit to indicate that the frame has been copied but not the bit

which indicates that the destination station recognizes the address In the former case there is no way for Token Ring source node to determine whether the frame it sent has become lost

Proponents of this approach suggest that reliability mechanisms such as the tracking of lost frames

are better left for implementation in layer of the OSI model Proponents of the set the bit

approach contend that this bit must be set to track lost frames but that the bit cannot be set

because the bridge is not the final destination

Translational bridges can create software gateway between the two domains To the SRB end

stations the translational bridge has ring number and bridge number associated with it and so it

looks like standard SRB The ring number in this case actually reflects the entire transparent

is another bridging domain To the transparent bridging domain the translational bridge simply

transparent bridge

information is When bridging from the SRB domain to the transparent bridging domain SRB

from the removed RIFs are usually cached for use by subsequent return traffic When bridging

if it has transparent bridging to the SRB domain the translational bridge can check the frame to see

unicast destination If the frame has multicast or broadcast destination it is sent into the SRB

domain as spanning tree explorer If the frame has unicast address the translational bridge looks added up the destination in the RIF cache If path is found it is used and the RIF information is to

Mixed-Media Bridging 31-3 Translational Bridging

the frame otherwise the frame is sent as spanning-tree explorer Because the two spanning-tree

implementations are not compatible multiple paths between the SRB and the transparent bridging

domains are typically not permitted

Figure 31-2 Figure 31-3 and Figure 31-4 are examples of frame conversions that can take place in

translational bridging

DASA SAP Control Data IEEE 802.3

DASA RIF SAP Control Data LACFC Token Ring

Figure 31-2 Frame Conversion Between IEEE 802.3 and Token Ring

Figure 31-2 shows the frame conversion between IEEE 8023 and Token Ring The destination and

source addresses DASA service access point SAP Logical Link Control LLC information

Control and data are passed to the corresponding fields of the destination frame The destination

and source address bits are reordered When bridging from IEEE 802.3 to Token Ring the length

field of the IEEE 802.3 frame is removed When bridging from Token Ring to IEEE 802.3the access

control byte and RIF are removed The RIF can be cached in the translational bridge for use by return

traffic

DASA Type Data Ethernet Type II

CFC DASA RIF SAP Control Vendor Code Type Dat

Figure 31-3 Frame Conversion Between Ethernet Type II and Token Ring SNAP

Figure 31-3 shows the frame conversion between Ethernet Type II and Token Ring Subnetwork

Access Protocol SNAP SNAP adds vendor and type codes to the data field of the Token Ring frame The destination and source addresses DASA type information and data are passed to the

corresponding fields of the destination frame The destination and source address bits are reordered

When bridging from Token Ring SNAP to Ethernet Type II the RIF information service access

point SAP LLC information Control and vendor code are removed The RIF can be cached in

the translational bridge for use by return traffic When bridging from Ethernet Type II to Token Ring

SNAP no information is removed

31-4 Internetworking Technology Overview Source-Route Transparent Bridging

Ethernet DASA OD5 F-r SAP Control Data

ACFC DASA RIF SAP Control Data Token Ring

31-4 Frame Conversion Between Ethernet and Token Figure Type II Ox8OD5 Format Ring

Figure 31-4 shows the frame conversion between Ethernet Type II Ox8OD5 format and Token Ring Ethernet Type II OxOD5 carries IBM SNA data in Ethernet frames The destination and

source addresses DASA service access point SAP LLC information Control and data are

passed to the corresponding fields of the destination frame The destination and source address bits

are reordered When bridging from Ethernet Type II Ox8OD5 to Token Ring the type and 80D5

header fields are removed When bridging from Token Ring to Ethernet Type II Ox8OD5 the RIF

is removed The RIF can be cached in the translational bridge for use by return traffic

Source-Route Transparent Brdgng

combine SRT SRT bridges implementations of the transparent bridging and SRB algorithms bridges use the routing information indicator Ru bit to distinguish between frames employing SRB and

in the and the frames employing transparent bridging If the Rh bit is RIF is present frame

bridge uses the SRB algorithm If the Ru bit is RIF is not present and the bridge uses transparent

bridging

mixed-media Like translational bridges SRT bridges are not perfect solutions to the problems of

bridging SRT bridges must still deal with the EthernetJToken Ring incompatibilities described

earlier SRT bridging is likely to require hardware upgrades to SRBs to allow them to handle the

increased burden of analyzing every packet Software upgrades to SRBs may also be required

Further in environments of mixed SRT bridges transparent bridges and SRBs source routes chosen

must traverse whatever SRT bridges and SRBs are available The resulting paths can potentially be

substantially inferior to spanning-tree paths created by transparent bridges Finally mixed SRB/SRT

bridging networks lose the benefits of SRT bridging so users will feel compelled to execute

complete cutover to SRT bridging at considerable expense Still SRT bridging permits the

coexistence of two incompatible environments and allows communication between SRB and

transparent bridging end nodes

Mixed-Media Bridging 31-5 Source-Route Transparent Bridging

31-6 Internetworking Technology Overview

CHAPTER 32

Simple Network Management Protocol

Background

Network Protocol Three development efforts impacted what was to become the Simple Management SNMP

with some High-Level Entity Management System HEMS Specifies management system never used outside its development interesting technical attributes Unfortunately HEMS was

sites and this eventually led to its demise

Initiated of network engineers to Simple Gateway Monitoring Protocol SGMP by group the Internet internetwork address the problems associated with managing rapidly growing large and businesses this connecting government agencies research institutions universities private Internet SGMP was effort produced protocol designed to manage gateways routers

implemented on many regional branches of the Internet

CMIP over TCP CMOTAdvocated by the developers of Open System interconnection OSI

based network management software and specifically of the Common Management information Control Protocol internetworks Protocol CMIP to help manage Transmission TCPbased

demerits of these three were Through the latter part of 1987 the merits and approaches frequently

Board committee was created to and hotly contested In early 1988 an Internet Activities JAB

is the that is for resolve the network management protocol debate The JAB group responsible the JAB committee that an technical development of the Internet protocols Eventually agreed the short-term and some OSI improved version of SGMP to be called SNMP would be solution

for its To based technology either CMOT or CMIP itself would be analyzed long-term suitability

framework for network called the ensure an easy upgrade path common management now Internet-standard Network Management Framework was created

for diverse commercial university and Today SNMP is the most popular protocol managing

research internetworks SNMP-related standardization activity continues even as vendors develop

and release state-of-the-art SNMP-based management applications SNMP is relatively simple

is to handle the difficult problems presented by protocol yet its feature set sufficiently powerful

management of heterogeneous networks

TechnWogy Basics

to facilitate the of management SNMP is an application-layer protocol designed exchange second and network information between network devices By using SNMP data such as packets per network and find and solve error rates network administrators can more easily manage performance network problems

32-1 Simple Network Management Protocol Technology Basics

Management Model

In SNMP agents are software modules that run in managed devices Agents compile information

about the managed devices in which they run and make this information available to network

management systems NMS5 via network management protocol SNMP This model is

graphically represented in Figure 32-1

Managed Managed Managed device device device

Figure 32-1 SNMP Management Model

managed device can be any type of node residing on network including computer hosts communication servers printers routers bridges and hubs Because some of these systems may have limited ability to run management software they may have relatively slow CPUs or limited memory for example management software must assume the lowest common denominator In other words management software must be built in such way as to minimize its own performance

impact on the managed device

Because managed devices contain lowest common denominator of management software the

management burden falls on the NMS Therefore NMSs are typically engineering workstation caliber computers that have fast CPUs megapixel color displays substantial memory and lots of disk space One or more NMSs may exist on any managed network NMSs run the network

management applications that present management information to users The user interface is

typically based on standardized graphical user interface GUI

Communication between managed devices and NMSs is governed by the network management protocol The Internet-standard Network Management Framework assumes remote-debugging

paradigm where managed devices maintain values for number of variables and report those on

demand to NMSs For example managed device might keep track of the following

Number and state of its virtual circuits

Number of certain kinds of error messages received

32-2 Internetworking Technology Overview Technology Basics

Number of bytes and packets in and out of the device

routers and other devices Maximum output queue length for internetworking

Broadcast messages sent and received

Network interfaces going down and coming up

Command Types

the If an NMS wishes to control managed device it can do so by sending message requiring

of its variables In devices respond to or managed device to change the value of one total managed

initiate four different types of commands

ReadsTo monitor managed devices NMSs read variables maintained by the devices

within the devices WritesTo control managed devices NMSs write variables stored managed

device Traversal operationsNMSs use these to determine which variables managed supports tables an IP table and to sequentially gather information in variable such as routing

devices to certain events to NMSs TrapsManaged use traps asynchronously report

Data Representation Differences

in the is by differences Exchange of information in managed network potentially compromised used the devices In other words computers represent data representation techniques by managed rationalized to allow communication information differently these incompatibilities must be function SNMP uses subset of Abstract between diverse systems An abstract syntax performs this

abstract created for OSI for this ASN.l defines Syntax Notation One ASN.l an syntax purpose is characteristic of something both packet formats and managed objects managed object simply

differs from which is object instance that can be managed managed object variable particular or tabular defining multiple related Managed objects may be scalar defining single instance instances

Management Database

Base which is essentially All managed objects are contained in the Management Information MIB abstract with individual data items as database of objects Logically Mffi is depicted as an tree

in the tree identifiers are like phone leaves Object identifiers uniquely identify MIB objects Object and are different organizations numbers in that they are organized hierarchically parts assigned by of codes by an international For example international phone numbers consist country assigned

as defined that United States phone numbers organization and the telephone number by country office and station number associated are further subdivided into an area code central number

identifiers are the International with that central office Similarly top-level MIB object assigned by Standardization/International Electrotechnical Commission ISO/JEC Lower- Organization for the associated The root and several prominent level object IDs are allocated by organizations in 32-2 branches of the MIB tree appear Figure

32-3 Simple Network Management Protocol Technology Basics

Figure 32-2 MW Tree

The MIB tree is extensible by virtue of experimental and private branches Vendors for example

define their can own private branches to include instances of their own products Currently all

standardization work is in the experimental branch

document called the Structure of Management Information SMI defines the structure of the MIB The SMI defines the following data types

Network addressesRepresent an address from particular protocol family Currently 32bit IP

addresses is the only instance of network addresses

CountersNonnegative integers that increase monotonically until they reach maximum value

when they wrap back to zero The total number of bytes received on an interface is an example of counter

GaugesNonnegative integers that can increase or decrease but latch at amaximum value The

length of an output packet queue in packets is an example of gauge

TicksHundredths of second since some event The time since an interface entered its current

state is an example of tick

This is used Opaque An arbitrary encoding to pass arbitrary information strings outside of the

strict data typing used by the SMI

Operations

itself is Nodes send SNMP simple request/response protocol can multiple requests without

response Four SNMP operations are defined

GetRetrieves an object instance from the agent

Get-nextA traversal operation that retrieves the next object instance from table or list within

an agent

SetSets object instances within an agent

TrapUsed by the agent to asynchronously inform the NMS of some event

32-4 Internetworking Technology Overview Message Format

Message Format

contain and SNMP messages two parts community name data The community name assigns an

access environment for set of NMSs using that community name NMSs within the community can

devices that do know be said to exist within the same administrative domain Because not the proper

community name are precluded from SNMP operations network managers have also used the

community name as weak form of authentication

The data portion of an SNMP message contains the specified SNMP operation get set and so on and associated operands Operands indicate the object instances involved in the SNMP transaction

SNMP messages are formally referred to as protocol data units PDUs Figure 32-3 shows the SNMP message format

Get set format Field length

in bytes Variable

Request-ID Error status Error index Variable bindings

Trap format Field length

in bytes Variable

Figure 32-3 SNMP Message Format

SNMP get and set PDUs consist of the following parts

Request-ID Associates requests with responses

Error-statusIndicates an error and an error type

Error-index Associates the error with particular object instance

Variable bindingsComprise the data of an SNMP PDU.Variable bindings associate particular

variables with their current values

Trap PDUs are slightly different from PDUs for other operations They consist of the following

parts

EnterpriseIdentifies the type of object generating the trap

Agent addressProvides the address of the object generating the trap

Generic trap typeProvides the generic trap type

SpecJlc trap codeProvides the specific trap code

Time stampProvides the amount of time that has elapsed between the last network

reinitialization and generation of this trap

Variable bindingsProvides list of variables containing interesting information about the trap

Simple Network Management Protocol 32-5 Message Format

32-6 Internetworking Technology Overview CHAPTER 33

IBM NeMiork Management

Background

IBM was one of the first companies to recognize the importance of complete integrated network framework management strategy In 1986 IBM proposed Open Network Architecture ONA describing generalized network management architecture Net View the premier product for

network management on an IBM mainframe is actually component of ONA NetView provides cohesive set of centralized network management services that allow users to monitor control and

reconfigure their Systems Network Architecture SNA networks

Since the introduction of ONA and NetView IBM has almost continually enhanced expanded and

otherwise altered its network management technology base Today IBM network management is the comprehensive and extremely complex This chapter describes the high-level basics of some of components of IBM network management

Functona Areas of Management

IBM divides network management into five user-based functions

control Configuration managementIdentifies physical and logical system resources and allows

of their relationships

Performance and accounting management Allows quantification measurement reportingand

control of the responsiveness availability utilization and usage of network component

Problem managementProvides problem detection diagnosis resolution and tracking and

control capabilities

and control distributed network Operations managementProvides the means to query

resources from central site

Change managementAllows planning control and application of additions deletions and modifications to system hardware microcode and software

These network management functions do not correlate perfectly with those proposed by the International Organization for Standardization ISO in its Open System Interconnection OSI

model The OSI and the IBM network management functions are compared in Figure 33-1

IBM Network Management 33-1 Functional Areas of Management

OSI IBM

Configuration management Configuration management

Performance management Performance and accounting

Accounting management management

Fault management Problem management

Security management

Operations management CD CD Change management Co

Figure 33-1 OSI and IBM Network Management Functions

Corifiguraton Management

and information Configuration management controls information describing both physical logical

consists of systems resources and their relationships to each other This information typically resource names addresses locations contacts and phone numbers IBMs configuration

management function corresponds very closely to OSIs concept of configuration management

network Through configuration management facilitiesusers can piaintain an inventory of resources

reflected Configuration management helps ensure that network configuration changes can be

expeditiously and accurately in the configuration management database Configuration management

data is used by problem management systems to compare version differences and to locate identify

and check the characteristics of network resources Change management systems can use

configuration management data to analyze the effect of changes and to schedule changes at times of minimal network impact

An SNA management service called query product identification retrieves software and hardware

physical information from the configuration management database The information retrieved is

sometimes called vital product data

Performance and Accounting Management

This SNA management function provides information about the performance of network resources

Through analysis of performance and accounting management data users can determine whether

network performance goals are being met

Performance and accounting management includes accounting monitoring of response times

availability utilization and component delay as well as performance tuning tracking and control Data from each of these functions can result in the initiation of problem determination procedures if

performance levels are not being met

33-2 Internetworking Technology Overview Functional Areas of Management

Problem Management

SNA management services define problem as an error condition that causes user to lose full

functionality of system resource SNA divides problem management into several areas

Problem determinationDetects problem and completes steps necessary for problem

diagnosis to begin Problem determination intends to isolate the problem to particular

subsystem such as hardware device software product microcode component or media segment

Problem diagnosisDetermines the precise cause of problem and the action required to solve

the problem If problem diagnosis is done manually it follows problem determination If it is

done automatically it is usually done simultaneously with problem determination so that the

results can be reported together

Problem bypass and recoveryAttempts to bypass problem either partially or completely

Normally this operation is temporary with the intent that complete problem resolution will

is less resolved follow but problem bypass may be permanent when the problem easily

Problem resolutionInvolves efforts required to eliminate the problem Problem resolution

usually begins after problem diagnosis is complete and often involves corrective action that

must be scheduled such as replacement of failed disk drive

Problem tracking and control Tracks the problem until final resolution Specifically if external

action is required to fix the problem the vital information describing the problem such as status

monitoring data and problem status reports are included in problem management record which

is entered into the problem database

Operations Management

central site Operations management involves management of distributed network resources from

It entails two sets of functions common operations services and operations management services SNAs Common operations services allow management of resources not explicitly addressed by

other management categories by allowing specialized communication with these resources through the new more capable applications Two very important services providing this capability are execute command and the resource management service The execute command provides

standardized means of executing remote command Resource management services provide way

to transport information in context-independent manner

Operations management services provide the ability to control remote resources through resource clocks activation resource deactivation command cancellation and the setting of network resource

Operations management services can be initiated automatically as result of system problem

notification forwarding thereby allowing automatic handling of remote problems

Change Management

Change management helps users control network or system changes by allowing the sending

retrieving installing and removing of change files at remote nodes Further change management

allows node activation Changes occur because either user requirements have changed or because

problem must be circumvented

Although problems cause change change can also cause problems Change management attempts

to minimize problems created by change through encouraging orderly change and by tracking changes

IBM Network Management 33-3 Principal Management Architectures and Platforms

Principa Management Architectures and PHatforms

IBM offers several management architectures and many important management platforms

The Open Network Archtecture Framework

The basic ONA framework is shown in Figure 33-2

Figure 33-2 ONA Framework

Focal points provide support for centralized network management operations They are the

management entities referred to in the general model described previously Focal points respond to

end station alerts maintain management databases and provide the user interface to the network

management operator

There are two kinds of focal points primary and secondary Primary focal points are as described

previously Secondary focal points provide backup for primary focal points and are used when

primary focal points fail

Nested focal points provide distributed management support for portions of large networks They

forward critical information to more global focal points

Collection points relay information from self-contained SNA subnetworks to focal points

Collection points are commonly used to forward data from IBM peer-to-peer networks into the ONA

hierarchy

Entry points are SNA devices that can implement ONA for themselves and other devices Most standard devices SNA are capable of being entry points

33-4 lnternetworking Technology Overview Principal Management Architectures and Platforms

Service points are systems that provide access into ONA for non-SNA devices Service points are

capable of sending network management information about non-SNA systems to focal points and

are also capable of receiving commands from focal points translating them into format acceptable

to non-SNA devices and forwarding them to non-SNA devices for execution Service points are

essentially gateways into ONA

SystemView

IBM announced SystemView in 1990 SystemView is blueprint for the creation of management

applications capable of managing multivendor information systems Specifically SystemView

describes how applications that manage heterogeneous networks will look feel and cooperate with other management systems Officially SystemView is Systems Application Architectures SAAs

systems management strategy

NetVew

It has the NetView is IBMs most comprehensive enterprise network management platform

following major parts

basic Command control facilityProvides the ability to control the network through operator

and file access commands to Virtual Telecommunications Access Method VTAM applications NetView and non-SNA controllers operating systems and Net View/PC an interface between devices

Hardware monitorMonitors the network and automatically issues alerts to the network when hardware operator error occurs

Session monitor Acts as VTAM performance monitor The session monitor provides software

problem determination and configuration management

function Help function Provides help for NetView management services users The help network includes browse facility help desk facility and library of commonly encountered

operation situations

Status monitorSummarizes and presents network status information

called Performance monitorMonitors the performance of communications controllers also

front-end processors or FEPs the Network Control Program NCP and attached resources

Distribution managerPlans schedules and tracks the distribution of data software and 3174

microcode in an SNA environment

LAN Network Manager

TB Ms LAN Network Manager LNM product is an OS/2 Extended Editionbased network local-area networks from management application that enables control of Token Ring LANs communicates with central support site NetView can see LNM activity for example alarmsLNM

LAN Station Manager LSM software which implements management agents in individual LAN

end stations Communication between LNM and LSM is effected using OSI Common Management

Protocol over the Information Services/Common Management Information CMIS/CMIP running connectionless Logical Link Control LLC protocol

SNMP

Protocol See IBM has recently added support for the Simple Network Management SNMP

information this Chapter 32 Simple Network Management Protocol for on protocol

IBM Network Management 33-5 Principal Management Architectures and Platforms

33-6 Internetworking Technology Overview

APPENDIX

References and Recommended Reading

Books and Periodcas

Massachusetts Addison- Apple Computer Inc AppleTalk Network System Overview Reading

Wesley Publishing Company Inc 1989

New Prentice Black Data Networks Concepts Theory and Practice Englewood Cliffs Jersey Hall 1989

Los California IEEE Black Physical Level Interfaces and Protocols Alamitos Computer

Society Press 1988

and the of Case J.D JR Davins M.S Fedor and ML Schoffstall Network Management Design SNMP ConneXions The Interoperability Report Vol March 1989

Case J.D JR Davins MS Fedor and ML Schoffstall Introduction to the Simple Gateway

Monitoring Protocol IEEE Network March 1988

Vol No March Clark SNAlnternetworking ConneXions The Interoperabilily Report 1992

The Vol Coltun OSPF An Internet Routing Protocol ConneXions Interoperability Report

No August 1989

and Architecture Vol 2nd ed Corner D.E Intern etworking with TCP/IP Principles Protocols

Englewood Cliffs New Jersey Prentice Hall 1991

York 1992 Davidson An Introduction to TCP/IP New York New Springer-Verlag

Publication Garcia-Luna-Aceves J.J Loop-FreeRouting Using Diffusing Computations pending

in IEEE/ACM Transactions on Networking Vol No 1993

Business One Irwin 1992 Green J.K Telecommunications 2nd ed Homewood Illinois

The Vol Hagans Components of OSI ES-IS Routing ConneXions Interoperability Report No August 1989

ConneXions The Hares Components of OSI Inter-Domain Routing Protocol IDRP 1992 Interoperability Report Vol No May

An Overview Joyce S.T and J.Q Walker II Advanced Peer-to-Peer Networking APPN 1992 ConneXions The Interoperability Report Vol No 10 October

No 1990 Kousky Bridging the Network Gap LAN Technology Vol January

Massachusetts Leinwand and Fang Network Management Practical Perspective Reading 1993 Addison-Wesley Publishing Company Inc

Vol 20 No 14 October 1991 Lippis The Internetwork Decade Data Communications

References and Recommended Reading A-i Books and Periodicals

McNamara J.E Local Area Networks Digital Press Educational Services Digital Equipment

Corporation 12 Crosby Drive Bedford MA 01730

Martin SNA IBMs Networking Solution Englewood Cliffs New Jersey Prentice Hall 1987

Martin with K.K Chapman and the ARBEN Group Inc LocalArea Networks Architectures and

Implementations Englewood Cliffs New Jersey Prentice Hall 1989

Medin The Great IGP DebatePart Two The Open Shortest Path First OSPF Routing

Protocol ConneXions The Interoperability Report Vol No 10 October 1991

Meijer Systems NetworkArchitecture tutorial New York New York John Wiley Sons Inc 1987

Miller M.A LAN Protocol Handbook San Mateo California MT Books 1990

OReilly and Todino Managing UUCP and Usenet 10th ed Sebastopol California OReilly Associates Inc 1992

Perlman Interconnections Bridges and Routers Reading Massachusetts Addison-Wesley

Publishing Company Inc 1992

Penman and Callon The Great IGP DebatePart One IS-IS and Integrated Routing ConneXions The Interoperability Report Vol No 10 October 1991

Rose M.T The Open Book Practical Perspective on OSI Englewood Cliffs New Jersey Prentice Hall 1990

Rose M.T The Simple Book An Introduction to Management of TCP/IP-based Internets

Englewood Cliffs New Jersey Prentice Hall 1991

Ross EE FDDIA Tutorial IEEE Communications Magazine Vol 24 No May 1986

Schlar S.K Inside X.25 Managers Guide New York New York McGraw-Hill Inc 1990

Schwartz Telecommunications Networks Protocols Modeling and Analysis Reading

Massachusetts Addison-Wesley Publishing Company Inc 1987

Sherman Data Communications Users Guide Englewood Cliffs New Jersey Prentice Hall 1990

Sidhu G.S R.F Andrews andA.B Oppenheimer Inside AppleTalk 2nd ed Reading

Massachusetts Addison-Wesley Publishing Company Inc 1990

Spragins J.D et al Telecommunications Protocols and Design Reading Massachusetts Addison-

Wesley Publishing Company Inc 1991

Stallings Data and Computer Communications New York New York Macmillan Publishing Company 1991

Stallings Handbook of Computer-Communications Standards Vols 13 Carmel Indiana HowardW Sams Inc 1990

Stallings Local Networks 3rd ed New York New York Macmillan Publishing Company 1990

Sunshine CA ed. ComputerNetworkArchitectures andProtocols 2nd ed New York New York Plenum Press 1989

Tannenbaum AS Computer Networks 2nd ed Englewood Cliffs New Jersey Prentice Hall 1988

Terplan Communication Networks Management Englewood Cliffs New Jersey Prentice Hall 1992

Tsuchiya Components of OSI IS-IS Intra-Domain Routing ConneXions The Interoperabiliiy Report Vol No August 1989

A-2 Internetworking Technology Overview Technical Publications and Standards

Tsuchiya Components of OSI Routing An Overview ConneXions The Interoperability Report Vol No August 1989

Zimmerman OSI Reference ModelThe ISO Model of Architecture for Open Systems

Interconnection IEEE Transactions on Communications COM-28 No April 1980

TechnicaH Pubhcatons and Standards

Advanced Micro Devices The Supernet Family for FDDI Technical Manual Number 09779A

Sunnyvale California 1989

The Supernet Family for FDDI 1989 Data Book Number 09734C Sunnyvale California 1989

American National Standards Institute X3T9.5 Committee FDDI Station Management SMT Rev 6.i 15 1990

Revised Text of ISO/DIS 8802/2 for the Second DIS Ballot Information Processing

SystemsLocal Area Networks Part Logical Link Control 1987-01 -14

Ti .606 Integrated Services Digital Network ISDNArchitectural Framework and

Service Description for Frame-Relaying Bearer Service 1990

Ti .617 Integrated Services Digital Network ISDNSignaling Specification for Frame

Relay Bearer Service for Digital Subscriber Signaling System Number DSS1 1991

Ti.6i8 Integrated Services Digital Network ISDNCore Aspects of Frame Protocol for Use with Frame Relay Bearer Service 1991

ATM Data Exchange Interface DXI Specification Version 1.0 Document ATM_FORUM/93-

590R1 August 41993

Banyan Systems Inc VINES Protocol Definition DA254-00 Rev 1.0 Westboro Massachusetts

February 1990

Belicore Generic System Requirements in Support of Switched Multi-Megabit Data Service

Technical Advisory TA-TSY-000772 October 1989

Local Access System Generic Requirements Objectives and Interface Support of Switched Issue December 1985 Multi-Megabit Data Service Technical Advisory TA-TSY-000773

Switched Multi-Megabit Data Service SMDS Operations Technology Network Element

Generic Requirements Technical Advisory TA-TSY-000774

Chapman J.T and Halabi HSSI High-Speed Serial Interface Design Specification Menlo Park California and Santa Clara California Cisco Systems and T3Plus Networking Inc 1990

Consultative Committee for International Telegraph and Telephone CCITT Data Communications

NetworksServices and Facilities Terminal Equipment and Interfaces Recommendations

X.29 Yellow Book Vol VIII Fascicle VIII.2 1980

CCITT Data Communications NetworksInterfaces Recommendations X.2UX.32 Red

Book Vol VIII Fascicle VIII.3 1984

DDN Protocol Handbook Four volumes 1989

Order Defense Conmiunications Agency Defense Data Network X.25 Host Interface Speclciation number AD A137 427 December 1983

From Phase IV Digital Equipment Corporation DECnet/OSI Phase Making the Transition EK PVTRN-BR 1989

References and Recommended Reading A-3 Technical Publications and Standards

DECserver 200 LocalArea Transport LAT Network Concepts AA-LD84A-TK June 1988

DIGITAL NetworkArchitecture Phase EK-DNAPV-GD-O01 September 1987

Digital Equipment Corporation Intel Corporation Xerox Corporation The Ethernet Local-Area

Network Data Link Layer and Physical Layer Specifications Ver 2.0 November 1982

Feinler E.J et al DDN Protocol Handbook Vols 14 NIC 50004 50005 50006 50007 Defense Communications Agency Alexandria Virginia December 1985

Garcia-Luna-Aceves J.J Unified Approach to Loop-Free Routing Using Distance Vectors or Link States ACM 089791-332-9/89/0009/0212 pp 212223 September 1989

Henirick and Lang Introduction to Switched Multi-megabit Data Service SMDS an Early Broadband Service Proceedings of the XIII International Switching Symposium ISS 90 May 27 June 1990

Hewlett-Packard Company X.25 The PSN Connection An Explanation of Recommendation X.25

5958-3402 October 1985

IEEE Project 802Local Metropolitan Area Networks Proposed Standard Distributed Queue

Dual Bus DQDB Subnetwork of Metropolitan Area Network MAN February 1990

IEEE 802.2Local Area Networks Standard 802.2 Logical Link Control ANSI/IEEE Standard October 1985

IEEE 802.3 LocalArea Networks Standard 802.3 Carrier Sense Multiple Access ANSIIIEEE Standard October 1985

International Business Machines Corporation ACF/NCP/VS network control program system

support programs general information GC3O-3058

Advanced Communications Function for VTAM ACFIVTAM general information introduction GS27-0462

Advanced Communications Function for VTAM general information concepts GS27- 0463

Dictionary of Computing SC2O-1699-7 1987

LocalArea Network Technical Reference SC3O-3883

Network Problem Determination Application general information GC34-2010

Synchronous Data Link Control general information GA27-3093

Systems Network Architecture concepts and products GC3O-3072

Systems NetworkArchitecture technical overview GC3O-3073-1 1985

Token-Ring Network Architecture Reference SC3O-3374

International Organization for Standardization Information Processing SystemOpen System

Interconnection Specification of Abstract Syntax Notation One ASN.1 International Standard 8824 December 1987

McGraw-HilIlData Communications McGraw-Hill Compilation of Data Communications

Standards Edition III 1986

National Security Agency Blacker Interface Control Document March 21 1989

Novell Inc IPX Router Specification Version 1.10 Part Number 107-000029-001 October 16 1992

A-4 Internetworking Technology Overview Technical Publications and Standards

Number 100 NetWare Link Services Protocol NLSP Specification Revision 0.9 Part 001708-001 March 1993

StrataCom Frame Relay Specification with Extensions 001-208966 Rev.1.0 September 18 1990

Xerox Corporation Internet Transport Protocols XNSS 029101 January 1991

References and Recommended Reading A-5 Technical Publications and Standards

A-6 Internetworking Technology Overview

INDEX

Numerics American National Standards Institute See ANSI ANSI 1-78-1 13-1 15-1 lOBase2 5-2 AppleTalk lOBaseS 5-2 and EIGRP 24-4 lOBaseT 5-2 and the OSI reference model 16-2 lOBroad36 5-2 attention packet 16-8 lBase5 5-2 3Com client-erver distributed system 16-1 extended network 16-5 and RIP 23-1 general operation 16-1 and XNS 22-1 22-3 media access protocols 16-2

network 16-4

nonextended network 16-5

Phase 16-1

15-615-7 AAL3/4 protocol address assignment 16-3 AAL5 15-715-8 transport-layer protocols 16-7

AARP 16-4 AppleTalk Address Resolution Protocol ABM 11-5 See AARP

Abstract Syntax Notation AppleTalk Data Stream Protocol See ASN.1 See ADSP

access classes SMDS 14-3 AppleTalk Echo Protocol access DQDB SMDS 14-3 See AEP

acknowledgment packet EIGRP 24-5 AppleTalk Filing Protocol ACSE 20-5 See APP

active link FDDI 7-6 AppleTalk Session Protocol active monitor Token Ring 6-4 See ASP

active state EIGRP 24-6 AppleTalk Transaction Protocol

adaptation layers ATM See ATP

See AAL3/4 AAL5 application service element Address Resolution Protocol See ASE

See ARP ARCnet as NetWare medium 19-2 address spoofing SMDS 14-2 area

addressing definition 2-6

general description 1-5 OSI 20-128-1

link-layer addresses 1-6 OSPF 25-2

network-layer addresses 1-6 area border router OSPF 25-2 25-4 adjacent routers OSPF ARM 11-5

ADSP 16-7 ARP

ABP 16-8 IP 18-6 AFT 20-4 VINES 21-221-6

APP 16-8 AS

algorithms inBGP 27-1

backoff 5-1 in EGP 26-1

beaconing 6-4 in EIGRP 24-6

Dijkstra 25-1 in IGRP 24-1 DUAL 24-3 inIP 18-6

routing 2-32-8 in OSPF 25-2

source-route bridging 30-130-3 ASE 20-5

SPF 25-4 ASN.l 20-5 32-3

STA 29-329-4 31-3 ASP 16-8

switching 2-2 Association Control Service Element

VINES routing 21-3 See ACSE

all-paths explorer RIF 30-3 asynchronous balanced mode See ABM

Index asynchronous response mode open 27-2 See ARM update 27-3 Transfer Mode Asynchronous packet formats 27-2 See ATM BIS 28-6

at-least-once transactions AppleTalk 16-7 BISDN 14-315-1 ATM black hole Frame Relay 13-2

adaptation layers 15-515-8 Border Gateway Protocol

ATM layer 15-315-5 See BGP

connectionless service 15-11 border intermediate system IDRP

general operation 15-1 See BIS

media supported 15-3 BPDU 29-4

multiplexing technology 15-2 BRI 10-2

network architecture 15-8 bridge protocol data unit

permanent-virtual-connection service 15-9 See BPDU

physical layer 15-3 bridge definition 34

ATM Forum 15-2 bridging

ATP 16-7 between transparent bridging and source-route bridging attachment unit interface domains 31-131-5

See AUI general operation 3-1

AUI 5-2 source-route 30-130-3

authentication technology basics 3-2

and BGP 27-227-3 translational 31-1 31-331-5 and OSPF 25-5 transparent 29-129-5

and SNMP 32-5 Broadband Integrated Services Digital Network

in OSI routing 28-2 See BISDN

authority and format identifier broadcast

SeeAFI networks 5-1

autonomous system subnetworks 28-2

See AS XNS addresses

autoreconfiguration Token Ring 6-4 directed 22-3

global 22-3 BSD UMX

and RIP 23-1 Btrieve NetWare 19-5

backbone OSPF 25-2

backoff algorithm Ethernet 5-1

Banyan VINES See VINES

Basic Rate Interface carrier sense multiple access/collision detection see BRI See CSMA/CD

beaconing Token Ring 6-4 CCIYI

Bell Communications Research and Frame Relay 13-1

See Bellcore and HSSI 8-1

Belicore and OSI 20-6

and SMDS 14-1 14-8 and SDLC 11-1

technical advisories 14-6 and X.25 12-1

Bellman-Ford routing algorithm 2-7 general description 1-7

BGP recommendations

and EIGRP 24-4 V.24 12-5

and OSPF 25-3 V.28 12-5

as the basis for IDRP 28-6 specifications

general operation 27-1 1.361 15-1

messages 1.430 10-2

keepalive 27-3 1.431 10-3

notification 27-3 1.450 10-4

Internetworking Technology Overview 1.451 10-4 common part convergence sublayer ATM 15-6 Q.920 10-4 communications controller IBM

Q.921 10-4 See FEP

Q.930 10-4 community name SNMP 32-5

Q931 10-4 computer-room interconnect bus cell loss field 15-5 See CI bus priority ATM cell relay protocols 14-8 concentrator FDDI 7-2 cells confederation IDRP 28-6

ATM 15-415-5 configuration management IBM 33-1 33-2 definition ATM 15-1 configuration message transparent bridging 29-4 SIP 14-6 confirmation OSI service primitive 20-3 change management IBM 33-133-3 Connectionless Network Protocol

CI bus 17-2 See CLNP circuits Connectionless Network Service

permanent virtual 12-3 See CLNS

switched virtual 12-3 connectionless server function ATM

virtual 12-3 13-1 See CLSF Cisco Systems connectionless service ATM 15-11

defining HSSI 8-1 Connection-Mode Network Protocol

developing IGRP 24-1 See CMNP

formation of Frame Relay consortium 13-1 Connection-Oriented Network Service Class network IP 18-4 See CONS Class network IP 18-4 CONS 20-2 Class network IP 18-4 Consultative Committee for International Telegraph and Class network IP 18-4 Telephone Class network IP 18-4 See CCITT

Clearinghouse protocol XNS 22-4 convergence client-server architecture ATM sublayer 15-6

AppleTalk 16-1 definition 2-4 NetWare 19-1 core routers ARPANET 26-1 VINES 21-2 counter SNMP data type 32-4

CLNP count-to-infinity problem RIP 23-3

and DECnet 17-2 Courier protocol XNS 22-4

and IGRP 24-1 CPE

and IS-IS 28-1 and SMDS 14-1

definition 20-2 multi-CPE configuration 14-4

CLNS single-CPE configuration 14-4

and DECnet 17-2 CSMAICD 5-I

definition 20-2 customer premises equipment CLP field ATM 15-5 See CPE CLSF 15-11

cluster controller SDLC 11-3 CMIP

and CMOT 32-1 and LAN Network Manager 33-5 DARPA 18-122-1 andTCP 32-1 DAS 7-2 definition 20-6 data circuit-terminating equipment CMIS/CMIP 33-5 See DCE CMNP and DECnet 17-2 data link connection identifier CMOT 32-1 See DLCI èollection points ONA 33-4 data network identification code command control facility NetView 33-5 See DNIIC Common Management Information Protocol data terminal equipment See CMIP See DTE common operations services IBM 33-3

Index Datagram Delivery Protocol Distributed Queue Dual Bus SeeDDP See DQDB DCE distribution manager NetView 33-5 and Frame Relay 13-1 DLCI 13-3 and LAPB circuits 1-5 DNA 17-1 and X.25 12-1 DNIC 12-4

DDCMP 11-1 17-2 domain

DDP 6-5 definition 2-6 DECnet OSI 20-128-1 addressing 17-3 OSPF 25-2 and CMNP 17-2 domain specific part andPLP 17-2 See DSP as the basis for IS-IS 28-1 DQDB 14-1 general operation 17-1 DS OSI 20-6 media-access 17-2 protocols DS-1 14-1 14-7 17-2 network-layer protocols DS-3 14-1 14-7

Phase IV routing 17-2 DS-3/E3 15-3 Phase frame format IV routing 17-3 DSAP 11-5

Phase definition 17-1 DSP 20-4

upper-layer protocols 17-6 DTE DECnet/OSI 17-1 and Frame Relay 13-1 Defense Advanced Research Projects Agency and LAPB circuits 11-5 See DARPA and X25 12-1

designated bridge transparent bridging 29-3 DTE/DCE interface

designated 29-3 port transparent bridging and Frame Relay 13-1 designated router OSPF 25-4 and HSSI 8-1

destination service access point and PPP 9-2 See DSAP andX.25 12-112-4

Diffusing Update Algorithm DUAL 24-3 See DUAL DUAL finite state machine EIGRP 24-4 Digital Data Communications Protocol Message dual homing FDDI 7-6 See DDCMP Dual IS-IS

Digital Equipment Corporation See Integrated IS-IS

and DDCMP 11-1 dual-attach station

and DECnet 17-1 See DAS

and Frame 13-1 Relay dynamic routing 2-5 18-6 and IS-IS 28-1

Digital Network Architecture See DNA

Digital Signal

See DS-l

token release 6-2 Digital Signal early Token Ring Echo Protocol See DS-3 XNS 22-4 EGP Dijkstra algorithm OSPF 25-1 and EIGRP 24-4 directed broadcasts XNS 22-3 and OSPF 25-3 directed multicasts XNS 22-3 compared with BGP 27-1 Directory Services See DS OSI general operation 26-1 message type discovery protocol ES-IS 28-2 error 26-4 discovery/recovery EIGRP 24-4 neighbor acquisition 26-3 distance vector routing neighbor reachability 26-3 algorithm 2-7 poll 26-3 protocol 24-125-1 routing update 26-3 distributed architecture advantages of 16-1 packet formats 26-2

ETA 1-7

Iriternetworking Technology Overview EIGRP

and AS 24-6

compatibility with IGRP 24-4 fast packet switching 14-8 15-1 external routes 24-6 FDDI internal routes 24-6 as DECnet medium 17-2 packet types 24-5 as NetWare medium 19-2 recomputation 24-6 as an AppleTalk medium 16-2 route tagging 24-6 as an ATM medium 15-3 Electronic Industries Association as an OSI medium 20-1 See ETA concentrator 7-2 emitter-coupled logic ECL 8-2 fault-tolerant features 7-47-6 encapsulation frame format 7-67-7 IPX 19-3 general operation 7-1 XNS 19-322-3 link types end system active 7-6 See ES passive 7-6 End System-to-Intermediate System priority scheme 7-3 SeeES-IS similarities to Token Ring 7-1 entry points ONA 33-4 specifications EP 22-4 Media Access Control 7-2 error message EGP 26-4 Physical Layer Medium Dependent 7-2 Error Protocol Physical Layer Protocol 7-2 See EP Station Management 7-2 ES traffic types 7-3 definition 2-3 FDDITaIk AppleTalk 16-2 hello packet format 28-3 PEP 11-333-5 in OSI networking 20-1 28-1 fiber ES-IS multimode 7-1 general operation 28-2 single mode 7-1 subnetwork types 28-2 Fiber Channel as an ATM medium 15-3 establishment controller SDLC 11-3 Fiber Distributed Data Interface Ethernet See FDDI and Token Ring MTU 31-2 File Transfer Protocol and transparent bridging 29-1 See FTP as DECnet medium 17-2 File Transfer Access and Management as NetWare medium 19-2 See FTAM as an AppleTalk medium 16-2 Filing protocol XNS 22-4 as an example of broadcast subnetwork 28-2 focal point ONA as an example of LAN 9-1 nested 33-4 differences between IEEE 802.3 and 5-2 primary 33-4 frame format 5-3 secondary 33-4 general operation 5-1 frame format EtherTalk AppleTalk 16-2 DECnet Phase IV routing 17-3 exactly once transactions AppleTalk 16-7 Ethernet 5-3 explorer frames 30-2 31-2 FDDI 7-67-7 extended network AppleTalk 16-5 Frame Relay 13-3 Exterior Gateway Protocol IEEE 802.3 5-3 See EGP IEEE 802.5 RIF 30-3 exterior router IP 18-6 SDLC 11-2 External Data Representation SIP level 14-6 See XDR SIP level 14-5 external routes EIGRP 24-6 Token Ring/IEEE 802.5 6-4

transparent bridging 29-4

X.25 12-3

Index Frame Relay High-Level Data Link Control

compared with ATM 15-9 See HDLC

consortium formation of 13-1 High-Level Entity Management System

frame format 13-3 See HEMS

general operation 13-1 High-Performance Parallel Interface LMI See HIPPI

extensions 13-2 High-Speed Serial Interface

global addressing 13-2 13-5 See HSSI

message format 13-4 HIPPI 8-2

multicasting 13-2 13-6 hold-downs 23-4 24-2

simple flow control 13-2 hop count

2-7 virtual circuit messages 13-2 general description network implementation 13-6 RIP limit 23-3 frame definition of 1-6 host/cost pairs VINES 21-4 FTAM 20-6 HSSI

FTP 18-9 and the OSI reference model 8-1

general operation 8-1

loopback tests 8-28-3

gateway

basic definition 3-1

in the Internet community 18-6 lAB

32-4 and 32-1 gauge data type SNMP SNMP subnetworks 28-2 1-7 general-topology ES-IS general description 32-4 get operation SNMP IBM 32-4 19-4 get-next operation SNMP andLU6.2 22-3 19-5 global broadcasts XNS and NetBIOS 22-3 network 33-133-5 global multicasts XNS and management GOSIP 20-2 and SDLC 11-1

and SRB 30-1

and SRT bridging 31-2 IBM network management and OSI 33-2

and SNA 33-2 33-3 33-4 33-5 hardware addresses and SNMP 33-5 See link-layer addresses definition of 33-1 hardware monitor NetView 33-5 functional areas of 33-1 HDLC LNM 33-5 and PPP 9-1 LSM 33-5 and VINES 21-2 NetView 33-5 differences between SDLC and 11-4 principal architectures and platforms 33-4 general operation 11-4 SystemView 33-5 header error control field ATM 15-5 IBM Token Ring network header as defined in OSI model 1-3 See Token Ring/IEEE 802.5 HEC field ATM 15-5 ICMP 18-7 hello packets ICMP Router Discovery Protocol EIGRP 24-5 See IRDP VINES 21-4 ICP VINES 21-2 21-6 Hello protocol OSPF 25-4 IDI 20-4 help function NetView 33-5 IDN 12-3 HEMS 32-1 IDP initial domain part 20-4 hierarchical routing 2-6 IDP Internet Datagram Protocol high-bandwidth applications ATM 15-1 description 22-2

packet format 22-3

Internetworking Technology Overview IDRP 28-128-6 interior gateway protocols IEEE 802.2 See IGP

11-1 and SDLC Interior Gateway Routing Protocol

as DECnet protocol 17-2 See IGRP

as an OSI protocol 20-1 interior router IP 18-6

general operation 11-5 intermediate system

IEEE 802.3 See IS

and FDDI 7-1 Intermediate System-to-Intermediate System Intradomain

and transparent bridging 29-1 Routing Exchange Protocol

as NetWare medium 19-2 See IS-IS

as an example of broadcast subnetwork 28-2 internal organization of the network layer

as an OSI protocol 20-1 See IONL

differences between Ethernet and 5-2 internal routes EIGRP 24-6

frame format 5-3 International Data Number

general operation 5-1 See IDN

IEEE 802.5 International Telecommunications Union

and FDDI 7-1 See ITU

and source-route bridging 30-1 30-2 Internet Activities Board

as NetWare medium 19-2 See lAB

as an OSI protocol 20-1 Internet community

compatibility of IBM Token Ring network and 6-1 and IGRP 25-1

general operation 6-1 and RIP 19-4

RIF 30-3 and XNS 22-3

IEEE 802.6 Internet Control Message Protocol

as the basis for SIP 14-1 See ICMP

MAC protocol 14-8 Internet Control Protocol

1-7 See IEEE general description ICP VINES

IGP 18-6 25-1 Internet Datagram Protocol

IGRP See IDP Internet Datagram Protocol

compatibility with EIGRP 24-4 Internet Packet Exchange

general operation 24-1 See IPX

stability features 24-2 Internet Protocol

timers SeeIP

flush 24-3 intradomam IS 2-3

hold time 24-3 IONL 20-2

invalid 24-3

update 24-3 and EIGRP 24-4 image traffic ATM 15-1 and IGRP 24-1 28-1 indication OSI service primitive 20-3 and Integrated IS-IS information frames and NetWare 19-4

SDLC 11-3 and OSPF 25-1

X.25/LAPB 12-5 and the OSI reference model 18-2 initial domain identifier and XNS 22-1

See IDI definition of 18-1 initial domain part network classes 18-4

See IDP initial domain part packet format 18-3

Institute of Electrical and Electronic Engineers subnet addresses 18-4 18-418-5

See IEEE subnet masks 18-5 25-6

Integrated IS-IS 28-1 TOS bits 25-5

Integrated Services Digital Network transport layer 18-8

See ISDN upper-layer protocols 18-9 inter-AS routing protocol BGP 27-1 IPX interdomain IS 2-3 and XNS 22-1

Interdomain Routing Protocol general operation 19-2

See IDRP packet format 19-2

Index IRDP 18-718-8

definition 2-3 LAN Network Manager hello format 28-3 packet See LNM in OSI networking 20-128-1 LAN Station Manager ISDN See LSM and Frame Relay 13-2 LAP 11-1 general operation 10-1 LAPB Layer 10-3 and SDLC 11-1 Layer 10-4 compared to HDLC and SDLC 11-5 Layer 10-4 frame types reference 10-2 points information frames 12-5 Is-Is supervisory frames 12-5 and EIGRP 24-4 unnumbered frames 12-5 and OSPF 25-1 general operation 12-4 general operation 28-1 LCP metrics 28-4 general operation 9-3 packet formats packet types IS-IS hello 28-428-5 link establishment 9-3 link-state 28-428-5 link maintenance 9-3 numbers packets 28-428-5 sequence link termination 9-3 redirect message 28-4 purpose of 9-1 routing hierarchy 28-3 Level router DECnet 17-5 so Level routing OSI 28-1 and FDDI 7-1 Level router DECnet 17-5 and HSSI 8-1 Level routing OSI 28-1 and IBM network management 33-1 Link Access Procedure and PPP 9-2 See LAP

and routing protocols 28-1 Link Access Procedure Balanced and SDLC 11-1 See LAPB and the OSI reference model 20-1 Link Control Protocol 1-7 general description See LCP TEC 32-3 link state advertisement network device names 2-3 See LSA network management functional areas link state routing algorithm 4-3 accounting management definition 2-7

configuration management 4-3 vs distance vector algorithm 24-1 fault management 4-4 link-layer addresses 1-6 performance management 4-2 link-state packet security management 4-4 See LSP specifications LLC 10589 28-1 and LAN Network Manager 33-5 10747 28-1 classes 3309-1979 9-2 Class 11-5 3309-1984/PDAD1 9-2 Class II 11-5 4335-1979 9-2 Class III 11-5 4335-1979/Addendum 1-1979 9-2 Class IV 11-5 7776 12-2 general operation 11-5 8208 12-2 sublayer 3-3 8348 20-2 types 8648 20-2 Type 11-5 9542 28-1 Type 11-5 TR9575 20-2 Type 11-5 TR 9577 20-2 LLC2 11-5 ITU 12-1

Internetworking Technology Overview LMI metropolitan area network extensions 13-2 See MAN

global addressing 13-2 13-5 MHS 20-6

message format 13-4 MIB 32-3

multicasting 13-2 13-6 mied-media bridging 31-131-5

simple flow control 13-2 modal dispersion FDDI 7-1

virtual circuit messages 13-2 monomode fiber

33-5 See fiber LNM single mode FDDI local management interface MSAU 6-1 6-4 See LMI multiaccess network OSPF 25-4 LocalTalk AppleTalk 16-2 multicast XNS Logical Link Control directed 22-3

SeeLLC global 22-3 logical link control sublayer multimode fiber FDDI 7-1

SeeLLC multipath routing LSA in IGRP 24-2

definition 25-1 in OSPF 25-5

types multiplexing technology AS external links advertisements 25-5 ATM 15-2 network links advertisements 25-5 TDM 15-2

router links advertisements 25-5 multistation access unit

summary links advertisements 25-5 See MSAU LSM 33-5

LSP 28-428-5

LU 6.2 IBM 19-4

Name Binding Protocol SeeNBP

NANP 14-6

MAC national terminal number

addresses 28-3 31-2 See NTN

sublayer 3-3 NAU 19-4

MAC-layer bridge 3-3 NBP 16-6

MAN 14-115-11 NCP NetWare Core Protocol 19-3 19-5

Management Information Base NCP Network Control Program 33-5

See MIB NCP Network Control Protocol 9-1

MAU 5-2 neighbor

Media Access Control sublayer EGP 26-2 See MAC OSPF 25-4 medium attachment unit neighbor acquisition message EGP 26-3

See MAU neighbor discover/recovery EIGRP 24-4 message format neighbor reachability message EGP 26-3 SNMP 32-5 neighbor tables EIGRP 24-5

Message Handling System nested focal points IBM 33-4 See MHS NET 20-328-3 message definition of 1-6 NetBIOS 19-5 metrics NetRPC protocol VINES 21-7

and BGP 27-2 NetView 33-1 33-5 and EGP 26-3 NetWare

and IGRP 24-1 and EIGRP 24-4

and IS-IS 28-4 and the OSI reference model 19-2

and OSPF 25-5 general operation 19-1

and RIP 23-1 media access 19-2

definition 2-1 2-7 network-layer protocols 19-2

shell 19-4

Index transport-layer protocols 19-4 NOS 19-1

upper-layer protocols 19-4 Novell

NetWare Core Protocol 19-5 and EIGRP 24-4

see NCP NetWare Core Protocol and NetWare 19-1

NetWare Loadable Module and RIP 23-1

See NLM and XNS 22-1

NetWare Message Handling System NRM 11-5 See NetWare MHS NSAP

NetWare MHS 19-5 20-6 addresses 20-3

NetWare Remote Procedure Call definition 20-3 28-3 See NetWare RPC n-selector OSI 20-3

NetWare RPC 19-5 NSP 17-6 network AppleTalk 16-4 NT1 10-1 network addressable unit NT1/2 10-2

See NAU NT2 10-i

Network Basic Input/Output System NTN 12-4 See NetBIOS NVE 16-6

Network Control Program See NCP Network Control Program

Network Control Protocol

See NCP network entity title OC-1 8-2 See NET Office Channel Network File System See OC-1 See NFS ONA 33-133-433-5 network management SNMP data type 32-4 IBM opaque Open Network Architecture functional areas 33-133-3 See ONA principal architecures and platforms 33433-5 Open Systems Interconnection SNMP 32-1 See OSI network management architecture 4-14-2 operations management IBM 33-1 Network Management Framework 32-1 32-2 operations management services IBM 33-3 Network 32-2 Management System OS network management systems 4-1 address format 20-4 network management ISO functional areas and IBM network management 33-1 accounting management 4-3 and IGRP 24-1 configuration management 4-3 ISO specifications 20-2 fault management 4-4 media-access protocols 20-1 security management 4-4 network service definition 20-2 network operating system network-layer protocols 17-2 20-2 See NOS routing protocols 28-1 network service access point service primitives See NSAP confirmation 20-3 Network Services Protocol indication 20-3 SeeNSP request 20-3 network-visible entity response 20-3 See NVE transport-layer protocols 20-4 NFS 18-9 20-6 upper-layer protocols 20-5 NLM 19-5 OSI reference model node AppleTalk 16-4 compatibility issues 1-4 nonbiocking interface ATM 15-3 information formats 1-3 normal response mode introduction 1-1 See NRM layers North American numbering plan application layer 1-4 See NANP link layer 1-5

10 Internetworking Technology Overview network layer 1-5 PEP 22-4

physical layer 1-5 performance and accounting management IBM 33-1

presentation layer 1-4 33-2

session layer 1-4 performance monitor NetView 33-5

transport layer 1-5 permanent virtual circuit OSPF See PVC

and EIGRP 24-4 permanent-virtual-connection service ATM 15-9

and IS-IS 28-2 Phase IV routing DECnet 17-2

database description packets 25-4 physical addresses

general operation 25-1 See link-layer addresses

hello packets 25-4 Physical Layer Convergence Protocol

link state acknowledgment packets 25-5 See PLCP

link state request packets 25-4 PLCP 14-7

link state update packets 25-5 PLP 17-2

packet formats 25-4 Point-to-Point Protocol

routing hierarchy 25-2 SeePPP

point-to-point subnetworks ES-IS 28-2

poison reverse updates 23-4 24-3 26-3 poll message EGP PPP

and LCP 9-3 packet assembler/disassembler andNCP 9-1 See PAD and NetWare 19-2 Packet Exchange Protocol frame format 9-2 See PEP general operation 9-1 packet format link layer 9-2 BGP 27-2 physical layer requirements 9-2 EGP 26-2 PRI 10-3 ES hello 28-228-3 Primary Rate Interface IDP 22-3 See PRI IP 18-3 Printer Access Protocol IPX 19-3 See PAP 16-8 IS hello 28-228-3 Printing Protocol 22-4 IS-IS 28-428-5 problem management IBM 33-1 33-3 OSPF 25-4 protocol data unit RIP 23-2 SeePDU TCP 18-8 protocol-dependent modules EIGRP 24-4 VIP 21-5 PSE 12-1 packets definition of 1-6 PSN 12-1 packet-switched network PT field ATM 15-5 See PSN public data network packet-switching exchange See PDN See PSE PVC PAD 12-2 and ATM 15-9 PAP 16-8 and Frame Relay 13-2 link 7-6 passive FDDI and X.25 12-3 state 24-6 passive EIGRP path splitting OSPF and IS-IS 28-2 payload type field ATM 15-5 PDN 12-1 PDU AAL3/4 ATM 15-6 QLLC 11-4 AAL5 ATM 15-7 Qualified Logical Link Control as used in networking literature 1-6 See QLLC SIP level SMDS 14-6 qualifier bit QLLC 11-6 28-4 SIP level SMDS 14-5 quality of service QOS

Index 11 24-5 query packets EIGRP route flush timer RIP 23-3 query product identification SNA 33-2 route invalid timer RIP 23-3 route states EIGRP

active 24-6

passive 24-6

routed protocols

AppleTalk 16-1 RARP 18-6 DECnet 17-1 RD 28-6 IP 18-2 RDI 28-6 IPX 19-2 recomputation EIGRP 24-6 OSI 20-2 redirect message IS-IS 28-4 VINES 21-5 Reliable Transfer Service Element vs routing protocols 2-8 See RTSE XNS 22-1 Reliable Transport Protocol router See RTP basic definition 3-1 Remote Operations Service Element exterior 18-6 See ROSE interior 18-6 remote procedure call 19-1 20-5 21-7 router of last resort 2-6 Remote Procedure Call Internet Protocol routing See RPC algorithm design goals 2-3 repeater definition 3-1 algorithm types 2-52-7 24-5 reply packets EIGRP definition of 2-1 service 20-3 request OSI primitive dynamic 18-6 Request For Comments metrics 2-7 See RFC multipath 24-225-5 24-5 request packets EIGRP static 18-6 response OSI service primitive 20-3 update message 2-2 26-3 Reverse Address Resolution Protocol routing algorithms See RARP Bellman-Ford 2-7 RFC distance vector 2-7 1058 23-2 link state 2-7 1163 27-1 shortest path first 2-7 1247 25-1 routing area 2-3 904 26-1 routing domain 2-3 assigned numbers 9-3 routing domain IDRP 28-6 general description 18-2 routing domain identifier IDRP 28-6 RIB 28-6 routing hierarchy IS-IS 28-2 28-3 RIF 30-3 routing information base IDRP 28-6 Ril bit 30-3 routing information field RIP See RIF and EIGRP 24-4 routing information indicator bit and IGRP 24-1 See Ru bit and IS-IS 28-2 Routing Information Protocol and NetWare 19-4 See RIP and OSPF 25-1 routing loop 23-3 24-3 and VINES 21-2 routing protocols and XNS 22-1 22-3 BGP 27-1 general operation 23-1 EGP 26-1 packet fonnat 23-2 IGRP 24-1 routing update timer 23-3 OSPF 25-1 stability features 23-323-4 RIP 23-1 root 29-3 bridge STA RTMP 16-6 root path cost STA 29-3 vs routed protocols 2-8 root port STA 29-3 routing table 2-1 ROSE 20-5

12 Internetworking Technology Overview Routing Table Maintenance Protocol service-specific convergence sublayer ATM 15-6 See RTMP session monitor NetView 33-5 Routing Table Protocol set operation SNMP 32-4

See RTP SGMP 32-1

timer 23-3 routing update RIP ships-in-the-night routing Integrated IS-IS 28-5 RPC 18-9 shortest-path-first routing algorithm 2-7 25-1 RS-232 12-5 8-19-2 Simple Gateway Monitoring Protocol RS-422 9-2 See SGMP RS-423 9-2 Simple Mail Transfer Protocol RTMP 16-623-124-4 See SMTP RTP Simple Network Management Protocol 21-2 general operation See SNMP 21-6 packet types single mode fiber FDDI 7-1 RTSE 20-5 single-attach station

See SAS

SIP

level 14-7

level 14-6

level 14-5 SAA 33-5 transmission system sublayer 14-7 SAP service access point 1-3 11-5 slow convergence SAP Service Advertisement Protocol See convergence and EIGRP 24-4 SMDS and NetWare 19-4 access classes 14-3 and XNS 22-1 and relationship to IEEE 802.6 14-3 SAR 15-6 compared with ATM 15-11 SAS 7-2 14-1 SDLC general operation network implementation 14-8 configurations 11-1 SIP 14-3 frame format 11-2 SMDS Interface Protocol frame types See SIP information 11-3 SMI 32-4 supervisory 11-3 SMTP 18-10 unnumbered 11-3 SNA general operation 11-1 and IBM network management 33-2 33-3 33-4 node types 11-1 33-5 SDU 15-3 and SDLC 11-1 and segmentation reassembly sublayer ATM 15-6 SNAP sequence numbers packet and NetWare 19-3 See SNP and XNS 22-3 Sequenced Packet Exchange SNI 14-1 See SPX SNMP Sequenced Packet Protocol and CMIP 20-6 See SPP and IBM network management 33-5 server and the Internet protocol suite 18-9 AppleTalk 16-1 general operation 32-1 NetWare 19-1 get operation 32-4 VINES 21-2 get-next operation 32-4 service access point message format 32-5 See SAP service access point set operation 32-4 Service Advertisement Protocol trap operation 32-4 See SAP Service Advertisement Protocol SNP 28-428-5 service data unit SNPA 28-3 See SDU SONET 15-3 service node VINES 21-2 service points ONA 33-5

Index 13 source service access point switching

See SSAP algorithms 2-2 source-route bridging definition 2-1

See SRB fast packet 14-8 source-route transparent bridging Synchronous Data Link Control

See SRT bridging See SDLC spanning-tree algorithm synchronous digital hierarchy SDH 8-2

See STA Synchronous Optical Network spanning-tree explorer RIF 30-3 See SONET specifically routed frame RIF 30-3 synchronous transfer mode

SPF algorithm OSPF 25-4 See STM split horizons 23-4 24-224-3 Systems Application Architecture

SPP 19-4 22-4 See SAA

SPX 19-4 Systems Network Architecture SRB SeeSNA

and STA 31-3 SystemView 33-5

bridging algorithm 30-2

explorer frames 31-2

general operation 30-1

MAC addresses 31-2

SRT bridging 30-131-231-5 T3 8-1 SSAP 11-5 T3plus Networking 8-1 SSCS 15-6 TA ISDN 10-1 STA 29-329-4 31-3 table of all known networks VINES 21-5 standards organizations 1-7 table of neighbors VINES 21-5 star topology tables ATM 15-2 AppleTalk routing 16-6 Token Ring 6-4 IP routing 18-618-7 static routing 2-5 18-6 neighbor 24-5 status monitor NetView 335 RIP routing 23-1 STM 15-2 topology 24-6 StreetTalk VINES 21-7 transparent bridging 29-1 29-2 Structure of Management Information zone information 16-7 See SMI TCP subnet addresses IP 18-4-i 8-5 and RIP 23-1 subnet masks 18-5 25-6 and SNMP 32-1 SubNetwork Access Point and SPP 22-4 See SNAP and TP4 20-4 subnetwork point of attachment and XNS 22-1 See SNPA background 18-1 subscriber network interface definition of 18-1 See SM packet format 18-8 supervisory frames TDM 13-1 15-2 SDLC 11-3 TEl 10-1 X25/LAPB 12-5 TE2 10-1 SYC TELENET 12-1 Frame Relay 13-2 Telnet 18-9 X.25 12-3 terminal adapter ISDN 10-1 Switched Multimegabit Data Service tick SNMP data type 32-4 See SMDS time-division multiplexing switched virtual circuit SeeTDM See SVC token

OSI protocols 20-5

Token Ring/IEEE 802.5 6-2

14 Internetworking Technology Overview Token Ring/IEEE 802.5

and Ethernet MTU 31-2

and IBM network management 33-5 UDP 18-8 18-9 19-422-4 as DECnet medium 17-2 Ungermann-Bass as NetWare medium 19-2 and RIP 23-1 as VINES medium 21-2 and XNS 22-1 22-3 as an AppleTalk medium 16-2 unicast XNS 22-3 of 6-1 compatibility unnumbered frames fault management mechanisms 6-4 SDLC 11-3 frame format 6-4 X.25/LAPB 12-5 6-1 general operation 24-5 update packets EIGRP priority system 6-3 User Datagram Protocol TokenTalk AppleTalk 16-2 See UDP topological database OSPF 25-2 User-Network Interface ATM 15-2 topology

ATM 15-2

IEEE 802.5 6-1

TokenRing 6-1

topology change message in transparent bridging networks 29-4 V.24 12-5

topology tables EIGRP 24-6 V.28 12-5 TOS 28-2 V.35 8-19-220-1

TPO 20-4 variable-length subnet masks 25-6 28-2

TP1 20-4 VCI 15-4

TP2 20-4 video traffic ATM 15-1 15-5 TP3 20-4 VINES 21-3 TP4 20-422-4 address selection process transaction ID AppleTalk 16-7 and RIP 23-1

translational bridging general operation 21-1

host/cost 21-4 general operation 31-131-3 pairs

translation challenges 31-231-3 network-layer protocols 21-2

Transmission Control Protocol routing algorithm 21-4 21-7 SeeTCP transport-layer services 21-7 transparent bridging upper-layer protocols and RIF 31-2 VINES Internetwork Protocol

andSTA 31-3 See VIP

frame format 29-4 VIP 21-2 general operation 29-1 general operation format 21-5 Transport Protocol packet See TP4 virtual channel identifier

32-4 See VCI trap operation SNMP channels 15-4 twisted pair virtual ATM circuit 13-1 as Token Ring/IEEE 802.5 medium 6-1 virtual 12-3 virtual connections 15-4 as an ATM medium 15-3 ATM

as an Ethernetl802.3 medium 5-2 virtual links 25-3

as an HSSI medium 8-2 virtual path identifier TYMNET 12-1 See VPI

15-4 type of service virtual paths ATM Method See TOS Virtual Telecommunications Access See VTAM

Virtual Terminal Protocol

See VTP

vital product data SNA 33-2

voice traffic ATM 15-1 15-5

VPI 15-4

Index 15 VTAM VTP 20-6

ZIP 16-6

ZIT 16-7

zone AppleTalk 16-4

Zone Information Protocol

See ZIP Windows 18-9 information table X.21 20-1 zone SeeZIT X.2lbis 12-5

X.25

and DECnet 17-2

and Frame Relay 13-1

and OSI 20-1

and OSI routing 28-2

and PPP 9-1

and SDLC 11-5

and VINES 21-2

compared with ATM 15-10

frame format 12-3

general operation 12-1

Layer 12-5

Layer 12-4

Layer 12-3

X.25 Packet-Level Protocol

See PLP

X.28 12-2

X29 12-2

X.3 12-2

X.500 20-6

XDR 18-9

Xerox Corporation

and Ethernet 5-1

and NetWare 19-1

and VINES 21-1

and XNS 22-1 XNS

and 3Com 22-3

and NetWare 19-1

and RIP 23-1

and SNAP 22-3

and the OSI reference model 22-1

and Ungermann-Bass 22-3

and VINES 21-1

encapsulation 22-3

general operation 22-1

media-access protocols 22-2

network-layer protocols 22-2

packet types 22-3

transport-layer protocols 22-4

upper-layer protocols 22-4

XON/XOFF flow control 13-2

16 Internetworking Technology Overview Corporate Headquarters Cisco Systems Inc

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Tel 415 326-1941

800 553-NETS 6387

Fax 415 326-1909

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