Chapter 2 Applications and Layered Architectures

Protocols, Services & Layering OSI Reference Model TCP/IP Architecture How the Layers Work Together Berkeley Sockets Application Layer Protocols & Utilities

1 Chapter 2 Applications and Layered Architectures

Protocols, Services & Layering

2 Layers, Services & Protocols z The overall communications process between two or more machines connected across one or more networks is very complex z Layering partitions related communications functions into groups that are manageable z Each layer provides a service to the layer above z Each layer operates according to a protocol z Let’s use examples to show what we mean

3 Web Browsing Application z World Wide Web allows users to access resources (i.e. documents) located in computers connected to the Internet z Documents are prepared using HyperText Markup Language (HTML) z A browser application program is used to access the web z The browser displays HTML documents that include links to other documents z Each link references a Uniform Resource Locator (URL) that gives the name of the machine and the location of the given document z Let’s see what happens when a user clicks on a link

4 1. DNS A. 64.15.247.200

Q. www.nytimes.com?

z User clicks on http://www.nytimes.com/ z URL contains Internet name of machine (www.nytimes.com), but not Internet address z Internet needs Internet address to send information to a machine z Browser software uses Domain Name System (DNS) protocol to send query for Internet address z DNS system responds with Internet address 5 2. TCP ACK

ACK, TCP Connection Request From: 64.15.247.200 Port 80 To:128.100.11.13 Port 1127

TCP Connection Request From: 128.100.11.13 Port 1127 To: 64.15.247.200 Port 80 z Browser software uses HyperText Transfer Protocol (HTTP) to send request for document z HTTP server waits for requests by listening to a well-known port number (80 for HTTP) z HTTP client sends request messages through an “ephemeral port number,” e.g. 1127 z HTTP needs a Transmission Control Protocol (TCP) connection between the HTTP client and the HTTP 6 server to transfer messages reliably 3. HTTP Content

200 OK

GET / HTTP/1.1 z HTTP client sends its request message: “GET …” z HTTP server sends a status response: “200 OK” z HTTP server sends requested file z Browser displays document z Clicking a link sets off a chain of events across the Internet! z Let’s see how protocols & layers come into play… 7 Protocols z A protocol is a set of rules that governs how two or more communicating entities in a layer are to interact z Messages that can be sent and received z Actions that are to be taken when a certain event occurs, e.g. sending or receiving messages, expiry of timers z The purpose of a protocol is to provide a service to the layer above

8 Layers z A set of related communication functions that can be managed and grouped together z Application Layer: communications functions that are used by application programs z HTTP, DNS, SMTP (email) z Transport Layer: end-to-end communications between two processes in two machines z TCP, User Datagram Protocol (UDP) z Network Layer: node-to-node communications between two machines z Internet Protocol (IP)

9 Example: HTTP z HTTP is an application layer protocol z Retrieves documents on behalf of a browser application program z HTTP specifies fields in request messages and response messages z Request types; Response codes z Content type, options, cookies, … z HTTP specifies actions to be taken upon receipt of certain messages

10 HTTP Protocol

GET HTTP HTTP Client Server Response

z HTTP assumes messages can be exchanged directly between HTTP client and HTTP server z In fact, HTTP client and server are processes running in two different machines across the Internet z HTTP uses the reliable stream transfer service

provided by TCP 11 Example: TCP z TCP is a transport layer protocol z Provides reliable byte stream service between two processes in two computers across the Internet z Sequence numbers keep track of the bytes that have been transmitted and received z Error detection and retransmission used to recover from transmission errors and losses z TCP is connection-oriented: the sender and receiver must first establish an association and set initial sequence numbers before data is transferred z Connection ID is specified uniquely by (send port #, send IP address, receive port #, receiver IP address)

12 HTTP uses service of TCP

HTTP HTTP client server Response GET

Port 1127 Port 80

GETResponseTCPTCP80, 1127 1127, 80TCPGETbytesResponse

13 Example: DNS Protocol z DNS protocol is an application layer protocol z DNS is a distributed database that resides in multiple machines in the Internet z DNS protocol allows queries of different types z Name-to-address or Address-to-name z Mail exchange z DNS usually involves short messages and so uses service provided by UDP z Well-known port 53

14 Local Authoritative Name Name Server Server 1 5 4 2 3 6

Root Name Server z Local Name Server: resolve frequently-used names z University department, ISP z Contacts Root Name server if it cannot resolve query z Root Name Servers: 13 globally z Resolves query or refers query to Authoritative Name Server z Authoritative Name Server: last resort z Every machine must register its address with at least two authoritative name servers 15 Example: UDP z UDP is a transport layer protocol z Provides best-effort datagram service between two processes in two computers across the Internet z Port numbers distinguish various processes in the same machine z UDP is connectionless z Datagram is sent immediately z Quick, simple, but not reliable

16 Summary z Layers: related communications functions z Application Layer: HTTP, DNS z Transport Layer: TCP, UDP z Network Layer: IP z Services: a protocol provides a communications service to the layer above z TCP provides connection-oriented reliable byte transfer service z UDP provides best-effort datagram service z Each layer builds on services of lower layers z HTTP builds on top of TCP z DNS builds on top of UDP z TCP and UDP build on top of IP

17 Chapter 2 Applications and Layered Architectures

OSI Reference Model

18 Why Layering? z Layering simplifies design, implementation, and testing by partitioning overall communications process into parts z Protocol in each layer can be designed separately from those in other layers z Protocol makes “calls” for services from layer below z Layering provides flexibility for modifying and evolving protocols and services without having to change layers below z Monolithic non-layered architectures are costly, inflexible, and soon obsolete

19 Open Systems Interconnection z Network architecture: z Definition of all the layers z Design of protocols for every layer z By the 1970s every computer vendor had developed its own proprietary layered network architecture z Problem: computers from different vendors could not be networked together z Open Systems Interconnection (OSI) was an international effort by the International Organization for Standardization (ISO) to enable multivendor computer interconnection

20 OSI Reference Model z Describes a seven-layer abstract reference model for a network architecture z Purpose of the reference model was to provide a framework for the development of protocols z OSI also provided a unified view of layers, protocols, and services which is still in use in the development of new protocols z Detailed standards were developed for each layer, but most of these are not in use z TCP/IP protocols preempted deployment of OSI protocols

21 7-Layer OSI Reference Model

Application Application End-to-End Protocols Application Application Layer Layer Presentation Presentation Layer Layer Session Session Layer Layer Transport Transport Layer Layer Network Network Network Network Layer Layer Layer Layer Data Link Data Link Data Link Data Link Layer Layer Layer Layer Physical Physical Physical Physical Layer Layer Layer Layer

22 Communicating End Systems One or More Network Nodes Physical Layer z Transfers bits across link z Definition & specification of the physical aspects of a communications link z Mechanical: cable, plugs, pins... z Electrical/optical: modulation, signal strength, voltage levels, bit times, … z functional/procedural: how to activate, maintain, and deactivate physical links… z Ethernet, DSL, cable modem, telephone modems… z Twisted-pair cable, coaxial cable optical fiber, radio, infrared, … 23 Data Link Layer z Transfers frames across direct connections z Groups bits into frames z Detection of bit errors; Retransmission of frames z Activation, maintenance, & deactivation of data link connections z Medium access control for local area networks z Flow control frames Data Link Data Link Layer Layer

Physical bits Physical Layer Layer 24 Network Layer z Transfers packets across multiple links and/or multiple networks z Addressing must scale to large networks z Nodes jointly execute routing algorithm to determine paths across the network z Forwarding transfers packet across a node z Congestion control to deal with traffic surges z Connection setup, maintenance, and teardown when connection-based

25 Internetworking Ethernet LAN z Internetworking is part of network layer and provides zzzzzz transfer of packets across multiple possibly dissimilar ATM networks Network ATM Switch z Gateways (routers) direct packets across networks ATM ATM HSwitch Switch

ATM H Switch NetNet 33 Net 1 G Net 1 G G G NetNet 5 5 H Net 2 G Net 4 G Net 2 H G = gateway

H = host 26 Transport Layer z Transfers data end-to-end from process in a machine to process in another machine z Reliable stream transfer or quick-and-simple single- block transfer z Port numbers enable multiplexing z Message segmentation and reassembly z Connection setup, maintenance, and release

Transport Transport Layer Layer

Network Network Network Network Layer Layer Layer Layer

27 Communication Network Application & Upper Layers z Application Layer: Provides services that are frequently Application required by applications: DNS, Application web acess, file transfer, email… Application Layer z Application Presentation Layer: machine- Layer independent representation of Presentation TransportLayer data… Layer Session z Session Layer: dialog Layer management, recovery from Transport Layer errors, … Incorporated into Application Layer

28 Headers & Trailers z Each protocol uses a header that carries addresses, sequence numbers, flag bits, length indicators, etc… z CRC check bits may be appended for error detection

Application APP DATA Application

Application AH APP DATA Application Layer Layer Transport Transport Layer TH AH APP DATA Layer

Network Network Layer NH TH AH APP DATA Layer

Data Link Data Link Layer DH NH TH AH APP DATA CRC Layer

Physical Physical 29 Layer bits Layer OSI Unified View: Protocols z Layer n in one machine interacts with layer n in another machine to provide a service to layer n +1 z The entities comprising the corresponding layers on different machines are called peer processes. z The machines use a set of rules and conventions called the layer-n protocol. z Layer-n peer processes communicate by exchanging Protocol Data Units (PDUs) n-PDUs

n n Entity Entity

30 Layer n peer protocol OSI Unified View: Services z Communication between peer processes is virtual and actually indirect z Layer n+1 transfers information by invoking the services provided by layer n z Services are available at Service Access Points (SAP’s) z Each layer passes data & control information to the layer below it until the physical layer is reached and transfer occurs z The data passed to the layer below is called a Service Data Unit (SDU) z SDU’s are encapsulated in PDU’s

31 Layers, Services & Protocols

n+1 n+1 entity entity

n-SDU n-SDU n-SAP n-SAP

n-SDU H n entity n entity H n-SDU

n-PDU 32 Interlayer Interaction

layer

N+1 user N provider N provider N+1 user

System A System B

33 Connectionless & Connection- Oriented Services z Connection-Oriented z Connectionless z Three-phases: z Immediate SDU 1. Connection setup transfer between two SAPs z No connection setup to initialize state z E.g. UDP, IP information z Layered services need 2. SDU transfer not be of same type 3. Connection release z TCP operates over IP z E.g. TCP, ATM z IP operates over ATM

34 Segmentation & Reassembly z A layer may impose a limit on the size of a data block (a) Segmentation that it can transfer for n-SDU implementation or other reasons z Thus a layer-n SDU may be n-PDU n-PDU n-PDU too large to be handled as a single unit by layer-(n-1) z Sender side: SDU is Reassembly segmented into multiple (b) PDUs n-SDU z Receiver side: SDU is reassembled from sequence of PDUs n-PDU n-PDU n-PDU

35 Multiplexing z Sharing of layer n service by multiple layer n+1 users z Multiplexing tag or ID required in each PDU to determine which users an SDU belongs to n+1 n+1 entity entity n+1 n+1 entity entity

n-SDU n-SDU n-SDU H n entity n entity

H n-SDU 36 n-PDU Summary z Layers: related communications functions z Application Layer: HTTP, DNS z Transport Layer: TCP, UDP z Network Layer: IP z Services: a protocol provides a communications service to the layer above z TCP provides connection-oriented reliable byte transfer service z UDP provides best-effort datagram service z Each layer builds on services of lower layers z HTTP builds on top of TCP z DNS builds on top of UDP z TCP and UDP build on top of IP

37 Chapter 2 Applications and Layered Architectures

TCP/IP Architecture How the Layers Work Together

38 Why Internetworking? z To build a “network of networks” or internet z operating over multiple, coexisting, different network technologies z providing ubiquitous connectivity through IP packet transfer z achieving huge economies of scale H

H NetNet 5 3 NetNet 5 1 G G G G NetNet 5 5 H G G NetNet 5 2 NetNet 5 4 H 39 Why Internetworking? z To provide universal communication services z independent of underlying network technologies z providing common interface to user applications

H Reliable Stream Service H NetNet 5 3 NetNet 5 1 G G G G NetNet 5 5 H G G NetNet 5 2 NetNet 5 4 H User Datagram Service 40 Why Internetworking? z To provide distributed applications z Any application designed to operate based on Internet communication services immediately operates across the entire Internet z Rapid deployment of new applications z Email, WWW, Peer-to-peer z Applications independent of network technology z New networks can be introduced below z Old network technologies can be retired

41 Internet Protocol Approach z IP packets transfer information across Internet Host A IP → router→ router…→ router→ Host B IP z IP layer in each router determines next hop (router) z Network interfaces transfer IP packets across networks

Host A Router Host B Router Transport Internet Transport Layer Layer Internet Layer Layer Network Internet Internet NetNet 5 1 Layer Interface Network Layer Router Interface Network Network Interface Internet Interface Layer NetNet 5 4 Network Net 2 NetNet 5 3 42 Net 5 Interface TCP/IP Protocol Suite

HTTP SMTP DNS RTP Distributed applications Reliable User TCP UDP stream datagram service service

Best-effort IP (ICMP, ARP) connectionless packet transfer

Network Network Network interface 1 interface 2 interface 3

43 Diverse network technologies Internet Names & Addresses

Internet Names Internet Addresses z Each host a a unique name z Each host has globally unique z Independent of physical logical 32 bit IP address location z Separate address for each z Facilitate memorization by humans physical connection to a network z z Domain Name Routing decision is done based on destination IP address z Organization under single administrative unit z IP address has two parts: z Host Name z netid and hostid z Name given to host z netid unique computer z netid facilitates routing z User Name z Dotted Decimal Notation: z Name assigned to user int1.int2.int3.int4 [email protected] (intj = jth octet) 128.100.10.13 DNS resolves IP name to IP address 44 Physical Addresses z LANs (and other networks) assign physical addresses to the physical attachment to the network z The network uses its own address to transfer packets or frames to the appropriate destination z IP address needs to be resolved to physical address at each IP network interface z Example: Ethernet uses 48-bit addresses z Each Ethernet network interface card (NIC) has globally unique Medium Access Control (MAC) or physical address z First 24 bits identify NIC manufacturer; second 24 bits are serial number z 00:90:27:96:68:07 12 hex numbers

Intel 45 Example internet Server PC Router (2,1) PPP (1,1) s (1,3) r Netid=2 (2,2) w Ethernet *PPP does not use addresses (netid=1) Workstation

(1,2)

Physical netid hostid address server 1 1 s workstation 1 2 w router 1 3 r router 2 1 - PC 2 2 - 46 Encapsulation

IP header IP Payload

Ethernet IP FCS header header IP Payload

z Ethernet header contains: z source and destination physical addresses z network protocol type (e.g. IP) 47 IP packet from workstation to server

Server PC Router (2,1) PPP (1,1) s (1,3) r (2,2) w Ethernet w, s (1,2), (1,1)

Workstation (1,2)

1. IP packet has (1,2) IP address for source and (1,1) IP address for destination 2. IP table at workstation indicates (1,1) connected to same network, so IP packet is encapsulated in Ethernet frame with addresses w and s 3. Ethernet frame is broadcast by workstation NIC and captured by server NIC 4. NIC examines protocol type field and then delivers packet to its IP layer 48 IP packet from server to PC

Server PC Router (2,1) (1,1), (2,2)

(1,1) s (1,3) r (2,2) w s, r (1,1), (2,2)

Workstation (1,2) 1. IP packet has (1,1) and (2,2) as IP source and destination addresses 2. IP table at server indicates packet should be sent to router, so IP packet is encapsulated in Ethernet frame with addresses s and r 3. Ethernet frame is broadcast by server NIC and captured by router NIC 4. NIC examines protocol type field and then delivers packet to its IP layer 5. IP layer examines IP packet destination address and determines IP packet should be routed to (2,2) 6. Router’s table indicates (2,2) is directly connected via PPP link

7. IP packet is encapsulated in PPP frame and delivered to PC 49 8. PPP at PC examines protocol type field and delivers packet to PC IP layer How the layers work together

(a) Server PC Router (2,1) (1,1) PPP s (1,3) r (2,2) Ethernet HTTP uses process-to-process Reliable byte stream transfer of TCP connection: Server socket: (IP Address, 80) (b) Server PC socket (IP Address, Eph. #) PC HTTP TCP uses node-to-node HTTP Unreliable packet transfer of IP TCP Server IP address & PC IP address TCP

IP IP IP

Network interface Network interface Network interface Internet Router Ethernet PPP 50 Encapsulation

TCP Header contains source & destination HTTP Request port numbers

IP Header contains source and destination TCP IP addresses; header HTTP Request transport protocol type

Ethernet Header contains IP TCP source & destination MAC HTTP Request addresses; header header network protocol type

Ethernet IP TCP FCS header header header HTTP Request 51 How the layers work together: Network Analyzer Example

Internet

z User clicks on http://www.nytimes.com/ z Ethereal network analyzer captures all frames observed by its Ethernet NIC z Sequence of frames and contents of frame can be examined in detail down to individual bytes

52 Top Pane Middle Pane Etherealshows windows shows frame/packet encapsulation for sequence a given frame

53 Bottom Pane shows hex & text Top pane: frame sequence TCP DNS Connection HTTP Query Setup Request & Response

54 Middle pane: Encapsulation

Ethernet Frame

Ethernet Protocol Type Destination and Source Addresses

55 Middle pane: Encapsulation And a lot of other stuff!

IP Packet

IP Source and Destination Addresses

Protocol Type 56 Middle pane: Encapsulation

TCP Segment

Source and Destination Port Numbers

GET

HTTP Request 57 Summary z Encapsulation is key to layering z IP provides for transfer of packets across diverse networks z TCP and UDP provide universal communications services across the Internet z Distributed applications that use TCP and UDP can operate over the entire Internet z Internet names, IP addresses, port numbers, sockets, connections, physical addresses

58 Chapter 2 Applications and Layered Architectures

Application Layer Protocols & IP Utilities

59 Telnet (RFC 854) z Provides general bi-directional byte-oriented TCP- based communications facility (Network Virtual Terminal) z Initiating machine treated as local to the remote host z Used to connect to port # of other servers and to interact with them using command line

Server process

NVT NVT

60 Network Virtual Terminal z Network Virtual Terminal z Lowest common denominator terminal z Each machine maps characteristics to NVT z Negotiate options for changes to the NVT z Data input sent to server & echoed back z Server control functions : interrupt, abort output, are-you-there, erase character, erase line z Default requires login & password

61 telnet z A program that uses the Telnet protocol z Establishes TCP socket z Sends typed characters to server z Prints whatever characters arrive z Try it to retrieve a web page (HTTP) or to send an email (SMTP)

62 File Transfer Protocol (RFC 959) z Provides for transfer of file from one machine to another machine z Designed to hide variations in file storage z FTP parameter commands specify file info z File Type: ASCII, EBCDIC, image, local. z Data Structure: file, record, or page z Transmission Mode: stream, block, compressed z Other FTP commands z Access Control: USER, PASS, CWD, QUIT, … z Service: RETR, STOR, PWD, LIST, …

63 FTP File Transfer

User interface

Control Server PI User PI connection

Data Server DTP User DTP connection

Server FTP User FTP

PI = Protocol interface DTP = Data transfer process 64 Two TCP Connections

Control connection Data connection z Set up using Telnet z To perform file transfer, protocol on well-known obtain lists of files, port 21 directories z FTP commands & replies z Each transfer requires new between protocol data connection interpreters z Passive open by user PI z PIs control the data with ephemeral port # transfer process z Port # sent over control z User requests close of connection control connection; z Active open by server server performs the close using port 20

65 FTP Replies

Reply Meaning

1yz Positive preliminary reply (action has begun, but wait for another reply before sending a new command). 2yz Positive completion reply (action completed successfully; new command may be sent). 3yz Positive intermediary reply (command accepted, but action cannot be performed without additional information; user should send a command with the necessary information). 4yz Transient negative completion reply (action currently cannot be performed; resend command later). 5zy Permanent negative completion reply (action cannot be performed; do not resend it).

x0z Syntax errors. x1z Information (replies to requests for status or help). x2z Connections (replies referring to the control and data connections). x3z Authentication and accounting (replies for the login process and accounting procedures). x4z Unspecified. 66 x5z File system status. FTP Client (192.168.1.132: 1421) establishes Control Connection to FTP Server (128.100.132.23: 21)

67 User types ls to list files in directory (frame 31 on control) FTP Server (128.100.132.23: 20) establishes Data Connection to FTP Client (192.168.1.132: 1422)

68 User types get index.html to request file transfer in control connection (frame 47 request); File transfer on new data connection (port 1423, fr. 48, 49, 51)

69 Hypertext Transfer Protocol z RFC 1945 (HTTP 1.0), RFC 2616 (HTTP 1.1) z HTTP provides communications between web browsers & web servers z Web: framework for accessing documents & resources through the Internet z Hypertext documents: text, graphics, images, hyperlinks z Documents prepared using Hypertext Markup Language (HTML)

70 HTTP Protocol z HTTP servers use well-known port 80 z Client request / Server reply z Stateless: server does not keep any information about client z HTTP 1.0 new TCP connection per request/reply (non-persistent) z HTTP 1.1 persistent operation is default

71 HTTP Typical Exchange

72 HTTP Message Formats z HTTP messages written in ASCII text z Request Message Format z Request Line (Each line ends with carriage return) z Method URL HTTP-Version \r\n z Method specifies action to apply to object z URL specifies object z Header Lines (Ea. line ends with carriage return) z Attribute Name: Attribute Value z E.g. type of client, content, identity of requester, … z Last header line has extra carriage return) z Entity Body (Content)

z Additional information to server 73 HTTP Request Methods

Request Meaning method GET Retrieve information (object) identified by the URL. HEAD Retrieve meta-information about the object, but do not transfer the object; Can be used to find out if a document has changed. POST Send information to a URL (using the entity body) and retrieve result; used when a user fills out a form in a browser. PUT Store information in location named by URL DELETE Remove object identified by URL TRACE Trace HTTP forwarding through proxies, tunnels, etc. OPTIONS Used to determine the capabilities of the server, or characteristics of a named resource.

74 Universal Resource Locator z Absolute URL z scheme://hostname[:port]/path z http://www.nytimes.com/

z Relative URL z /path z /

75 HTTP Request Message

76 HTTP Response Message z Response Message Format z Status Line z HTTP-Version Status-Code Message z Status Code: 3-digit code indicating result z E.g. HTTP/1.0 200 OK z Headers Section z Information about object transferred to client z E.g. server type, content length, content type, … z Content z Object (document)

77 HTTP Response Message

78 HTTP Proxy Server & Caching z Web users generate large traffic volumes z Traffic causes congestion & delay z Can improve delay performance and reduce traffic in Internet by moving content to servers closer to the user z Web proxy servers cache web information z Deployed by ISPs z Customer browsers configured to first access ISPs proxy servers z Proxy replies immediately when it has requested object or retrieves the object if it does not 79 Cookies and Web Sessions z Cookies are data exchanged by clients & servers as header lines z Since HTTP stateless, cookies can provide context for HTTP interaction z Set cookie header line in reply message from server + unique ID number for client z If client accepts cookie, cookie added to client’s cookie file (must include expiration date) z Henceforth client requests include ID z Server site can track client interactions, store these in a separate database, and access database to prepare appropriate responses

80 Cookie Header Line; ID is 24 hexadecimal numeral

81 PING z Application to determine if host is reachable z Based on Internet Control Message Protocol z ICMP informs source host about errors encountered in IP packet processing by routers or by destination host z ICMP Echo message requests reply from destination host z PING sends echo message & sequence # z Determines reachability & round-trip delay z Sometimes disabled for security reasons

82 PING from NAL host

Microsoft(R) Windows DOS (c)Copyright Microsoft Corp 1990-2001. C:\DOCUME~1\1>ping nal.toronto.edu Pinging nal.toronto.edu [128.100.244.3] with 32 bytes of data: Reply from 128.100.244.3: bytes=32 time=84ms TTL=240 Reply from 128.100.244.3: bytes=32 time=110ms TTL=240 Reply from 128.100.244.3: bytes=32 time=81ms TTL=240 Reply from 128.100.244.3: bytes=32 time=79ms TTL=240 Ping statistics for 128.100.244.3: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 79ms, Maximum = 110ms, Average = 88ms C:\DOCUME~1\1>

83 Traceroute z Find route from local host to a remote host z Time-to-Live (TTL) z IP packets have TTL field that specifies maximum # hops traversed before packet discarded z Each router decrements TTL by 1 z When TTL reaches 0 packet is discarded z Traceroute z Send UDP to remote host with TTL=1 z First router will reply ICMP Time Exceeded Msg z Send UDP to remote host with TTL=2, … z Each step reveals next router in path to remote host

84 Traceroute from home PC to university host

Home Network

Rogers Cable ISP

Shaw Net Hydro One

Ontario Net

University of Toronto

85 ipconfig z Utility in Microsoft® Windows to display TCP/IP information about a host z Many options z Simplest: IP address, subnet mask, default gateway for the host z Information about each IP interface of a host z DNS hostname, IP addresses of DNS servers, physical address of network card, IP address, … z Renew IP address from DHCP server

86 netstat z Queries a host about TCP/IP network status z Status of network drivers & their interface cards z #packets in, #packets out, errored packets, … z State of routing table in host z TCP/IP active server processes z TCP active connections

87 netstat protocol statistics

IPv4 Statistics ICMPv4 Statistics

Packets Received = 71271 Received Sent Received Header Errors = 0 Messages 10 6 Received Address Errors = 9 Errors 0 0 Datagrams Forwarded = 0 Destination Unreachable 8 1 Unknown Protocols Received = 0 Time Exceeded 0 0 Received Packets Discarded = 0 Parameter Problems 0 0 Received Packets Delivered = 71271 Source Quenches 0 0 Output Requests = 70138 Redirects 0 0 Routing Discards = 0 Echos 0 2 Discarded Output Packets = 0 Echo Replies 2 0 Output Packet No Route = 0 Timestamps 0 0 Reassembly Required = 0 Timestamp Replies 0 0 Reassembly Successful = 0 Address Masks 0 0 Reassembly Failures = 0 Address Mask Replies 0 0 Datagrams Successfully Fragmented = 0 Datagrams Failing Fragmentation = 0 TCP Statistics for IPv4 Fragments Created = 0 Active Opens = 798 UDP Statistics for IPv4 Passive Opens = 17 Failed Connection Attempts = 13 Datagrams Received = 6810 Reset Connections = 467 No Ports = 15 Current Connections = 0 Receive Errors = 0 Segments Received = 64443 Datagrams Sent = 6309 Segments Sent = 63724 88 Segments Retransmitted = 80 tcpdump and Network Protocol Analyzers z tcpdump program captures IP packets on a network interface (usually Ethernet NIC) z Filtering used to select packets of interest z Packets & higher-layer messages can be displayed and analyzed z tcpdump basis for many network protocol analyzers for troubleshooting networks z We use the open source Ethereal analyzer to generate examples z www.ethereal.com

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