15-441 Computer Networking Outline IP Service Model Ipv4 Header Fields
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Ip Fragmentation
NETWORKING CASE STUDY IN STEM EDUCATION - IP FRAGMENTATION M. Mikac1, M. Horvatić2, V. Mikac2 1Inter-biz, Informatic Services (CROATIA) 2University North (CROATIA) Abstract In the last decade, or even longer, computer networking has been a field that cannot be overseen in technical and STEM education. While technological development and affordable prices brought powerful network devices to the end-user, all the networking principles are still based (and probably will remain so) on old protocols developed back in the ‘60s and the ‘70s of the twentieth century. Therefore, it can be expected that understanding the basics of networking principles is something that future engineers should be familiar with. The global network of today, the Internet, is based on a TCP/IP stack of protocols. That is the fact that is not to be changed - the most important change that seems to be predictable will be wider acceptance and usage of a newer version of Internet Protocol (IP) - IPv6 increases its adoption in the global network but it is still under 30%. Even though different modifications of certain transport (TCP, UDP) and network (IP) protocols appeared, essentially the basics are still based on old protocols and most of the network traffic is still using the good old TCP/IP stack. In order to explain the basic functional principles of today’s networks, different kinds of case studies in real-networks or emulated environments can be introduced to students. Among those, one of the case studies we use in our education is related to explaining, the so-called, IP fragmentation - the process that sometimes "automagically" appears in IP network protocol-based networks when certain constraints are met. -
Cisco − IP Fragmentation and PMTUD Cisco − IP Fragmentation and PMTUD Table of Contents
Cisco − IP Fragmentation and PMTUD Cisco − IP Fragmentation and PMTUD Table of Contents IP Fragmentation and PMTUD.........................................................................................................................1 Introduction..............................................................................................................................................1 IP Fragmentation and Reassembly...........................................................................................................1 Issues with IP Fragmentation............................................................................................................3 Avoiding IP Fragmentation: What TCP MSS Does and How It Works...........................................4 Problems with PMTUD.....................................................................................................................6 Common Network Topologies that Need PMTUD...........................................................................9 What Is PMTUD?..................................................................................................................................11 What Is a Tunnel?..................................................................................................................................11 Considerations Regarding Tunnel Interfaces..................................................................................12 The Router as a PMTUD Participant at the Endpoint of a Tunnel..................................................13 -
RFC 8900: IP Fragmentation Considered Fragile
Stream: Internet Engineering Task Force (IETF) RFC: 8900 BCP: 230 Category: Best Current Practice Published: September 2020 ISSN: 2070-1721 Authors: R. Bonica F. Baker G. Huston R. Hinden O. Troan F. Gont Juniper Networks Una�liated APNIC Check Point Software Cisco SI6 Networks RFC 8900 IP Fragmentation Considered Fragile Abstract This document describes IP fragmentation and explains how it introduces fragility to Internet communication. This document also proposes alternatives to IP fragmentation and provides recommendations for developers and network operators. Status of This Memo This memo documents an Internet Best Current Practice. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on BCPs is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8900. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. -
07-Fragmentation+Ipv6+NAT Posted.Pptx
IP Fragmentation & Reassembly Network links have MTU (maximum transmission unit) – the largest possible link-level frame Computer Networks • different link types, different MTUs • not including frame header/trailer fragmentation: • in: one large datagram but including any and all headers out: 3 smaller datagrams above the link layer Large IP datagrams are split up reassembly Lecture 7: IP Fragmentation, (“fragmented”) in the network IPv6, NAT • each with its own IP header • fragments are “reassembled” only at final destination (why?) • IP header bits used to identify and order related fragments IPv4 Packet Header Format IP Fragmentation and Reassembly 4 bits 4 bits 8 bits 16 bits Example: 4000-byte datagram unique per datagram hdr len Type of Service MTU = 1500 bytes usually IPv4 version per source (bytes) (TOS) Total length (bytes) 3-bit One large datagram length ID IP fragmentation use Identification 13-bit Fragment Offset fragflag offset flags becomes several =4000 =x =0 =0 upper layer protocol 20-byte to deliver payload to, Time to Protocol Header Checksum Header smaller datagrams e.g., ICMP (1), UDP (17), Live (TTL) 1480 bytes in offset = TCP (6) • all but the last fragments data field 1480/8 Source IP Address must be in multiple of 8 length ID fragflag offset Destination IP Address bytes =1500 =x =MF =0 e.g. timestamp, • offsets are specified in record route, Options (if any) length ID fragflag offset source route unit of 8-byte chunks =1500 =x =MF =185 • IP header = 20 bytes (1 Payload (e.g., TCP/UDP packet, max size?) length ID fragflag offset -
TCP/IP Illustrated TCP/IP Illustrated, Volume 1 the Protocols W
TCP/IP Illustrated TCP/IP Illustrated, Volume 1 The Protocols W. Richard Stevens Contents Preface Chapter 1. Introduction 1.1 Introduction 1.2 Layering 1.3 TCP/IP Layering 1.4 Internet Addresses 1.5 The Domain Name System 1.6 Encapsulation 1.7 Demultiplexing 1.8 Client-Server Model 1.9 Port Numbers 1.10 Standardization Process 1.11 RFCs 1.12 Standard, Simple Services 1.13 The Internet 1.14 Implementations 1.15 Application Programming Interfaces 1.16 Test Network 1.17 Summary Chapter 2. Link Layer 2.1 Introduction 2.2 Ethernet and IEEE 802 Encapsulation 2.3 Trailer Encapsulation 2.4 SLIP: Serial Line IP 2.5 Compressed SLIP file:///F|/USER/DonahuJ/tcpip/tcpip_ill/index.htm (1 of 9) [1/23/2002 10:11:12 AM] TCP/IP Illustrated 2.6 PPP: Point-to-Point Protocol 2.7 Loopback Interface 2.8 MTU 2.9 Path MTU 2.10 Serial Line Throughput Calculations 2.11 Summary Chapter 3. IP: Internet Protocol 3.1 Introduction 3.2 IP Header 3.3 IP Routing 3.4 Subnet Addressing 3.5 Subnet Mask 3.6 Special Case IP Address 3.7 A Subnet Example 3.8 ifconfig Command 3.9 netstat Command 3.10 IP Futures 3.11 Summary Chapter 4. ARP: Address Resolution Protocol 4.1 Introduction 4.2 An Example 4.3 ARP Cache 4.4 ARP Packet Format 4.5 ARP Examples 4.6 Proxy ARP 4.7 Gratuitous ARP 4.8 arp Command 4.9 Summary Chapter 5. RARP: Reverse Address Resolution Protocol 5.1 Introduction 5.2 RARP Packet Format 5.3 RARP Examples 5.4 RARP Server design 5.5 Summary Chapter 6. -
Chapter 14 in Stallings 10Th Edition
The Internet Protocol Chapter 14 in Stallings 10th Edition CS420/520 Axel Krings Page 1 Sequence 16 Table 14.1 Internetworki ng Terms (Table is on page 429 in the textbook) CS420/520 Axel Krings Page 2 Sequence 16 1 Host A Host B App X App Y App Y App X Port 1 2 3 2 4 6 Logical connection (TCP connection) TCP TCP Global internet IP address IP Network Access Network Access Protocol #1 Protocol #2 Logical connection Physical Subnetwork attachment (e.g., virtual circuit) Physical point address Router J IP NAP 1 NAP 2 Network 1 Network 2 Physical Physical Figure 14.1 TCP/IP Concepts CS420/520 Axel Krings Page 3 Sequence 16 Why we do not want Connection Oriented Transfer CS420/520 Axel Krings Page 4 Sequence 16 2 Connectionless Operation • Internetworking involves connectionless operation at the level of the Internet Protocol (IP) IP ••Initially developed for the DARPA internet project ••Protocol is needed to access a particular network CS420/520 Axel Krings Page 5 Sequence 16 Connectionless Internetworking • Advantages —FlexiBility —Robust —No unnecessary overhead • UnreliaBle —Not guaranteed delivery —Not guaranteed order of delivery • Packets can take different routes —ReliaBility is responsiBility of next layer up (e.g. TCP) CS420/520 Axel Krings Page 6 Sequence 16 3 LAN 1 LAN 2 Frame relay WAN Router Router End system (X) (Y) End system (A) (B) TCP TCP IP IP IP IP t1 t6 t7 t10 t11 t16 LLC LLC LLC LLC t2 t5 LAPF LAPF t12 t15 MAC MAC MAC MAC t3 t4 t8 t9 t13 t14 Physical Physical Physical Physical Physical Physical t1, t6, t7, t10, t11, -
Security in Broadband Satellite Systems for the Aeronautical and Other Scenarios
Security in broadband satellite systems for the aeronautical and other scenarios Double-diplôme Ingénieur SUPAERO (ISAE) – Enginyeria de telecomunicacions (UPC) Projet de fin d’études (Master Thesis Report) by Dirk Gómez Depoorter SUPAERO supervisor: José Radzik TriaGnoSys supervisor: Eriza Hafid Fazli 2011 Munich, Germany 1 Table of Contents TABLE OF CONTENTS ........................................................................................................................................ 2 LIST OF TABLES ................................................................................................................................................. 6 LIST OF FIGURES ............................................................................................................................................... 7 ABBREVIATIONS ............................................................................................................................................... 9 1 INTRODUCTION ..................................................................................................................................... 10 2 THE ESA REQUEST .................................................................................................................................. 11 2.1 THE PROJECT ..................................................................................................................................... 11 2.2 OBJECTIVES ...................................................................................................................................... -
Fragmentation Overlapping Attacks Against Ipv6: One Year Later
Fragmentation (Overlapping) Attacks One Year Later... Antonios Atlasis [email protected] Troopers 13 – IPv6 Security Summit 2013 Troopers13 – IPv6 Security Summit 2013 Antonios Atlasis Bio ● Independent IT Security analyst/researcher. ● MPhil Univ. of Cambridge, PhD NTUA, etc. ● Over 20 years of diverse Information Technology experience. ● Instructor and software developer, etc. ● More than 25 scientific and technical publications in various IT fields. ● E-mail: [email protected] [email protected] Troopers13 – IPv6 Security Summit 2013 Antonios Atlasis Agenda ● Background – Fragmentation in IPv4. – Fragmentation in IPv6. – IDS Insertion / Evasion using fragmentation. – A few words about Scapy ● Discussed cases: – Atomic Fragments – Identification number issues – Tiny Fragments – Firewall evasions – ...Delayed fragments – Simple Fragmentation Overlapping / Paxson Shankar model – 3-packet generation overlapping – Double fragments ● Conclusions Troopers13 – IPv6 Security Summit 2013 Antonios Atlasis Fragmentation in IPv4 Troopers13 – IPv6 Security Summit 2013 Antonios Atlasis IP Fragmentation ● Usually a normal and desired (if required) event. ● Required when the size of the IP datagram is bigger than the Maximum Transmission Unit (MTU) of the route that the datagram has to traverse (e.g. Ethernet MTU=1500 bytes). ● Packets reassembled by the receiver. Troopers13 – IPv6 Security Summit 2013 Antonios Atlasis Fragmentation in IPv4 ● Share a common fragment identification number (which is the IP identification number of the original datagram). ● Define its offset from the beginning of the corresponding unfragmented datagram, the length of its payload and a flag that specifies whether another fragment follows, or not. ● In IPv4, this information is contained in the IPv4 header. ● Intermediate routers can fragment a datagram (if required), unless DF=1. -
Common Lower-Layer Protocols
COMMON LOWER-LAYER PROTOCOLS Whether troubleshooting latency issues, identifying malfunctioning applications, or zeroing in on security threats in order to be able to spot abnormal traffic, you must first understand nor- mal traffic. In the next couple of chapters, you’ll learn how normal network traffic works at the packet level. We’ll look at the most common protocols, including the workhorses TCP, UDP, and IP, and more commonly used application-layer protocols such as HTTP, DHCP, and DNS. Each protocol section has at least one associated capture file, which you can download and work with directly. This chapter will specifically focus on the lower-layer protocols found in reference to layers 1 through 4 of the OSI model. These are arguably the most important chapters in this book. Skipping the discussion would be like cooking Sunday supper without cornbread. Even if you already have a good grasp of how each protocol functions, give these chapters at least a quick read in order to review the packet structure of each. Practical Packet Analysis, 2nd Edition © 2011 by Chris Sanders Address Resolution Protocol Both logical and physical addresses are used for communication on a network. The use of logical addresses allows for communication between multiple networks and indirectly connected devices. The use of physical addresses facilitates communication on a single network segment for devices that are directly connected to each other with a switch. In most cases, these two types of addressing must work together in order for communication to occur. Consider a scenario where you wish to communicate with a device on your network. -
Measuring and Comparing the Stability of Internet Paths Over Ipv4
Measuring and Comparing the Stability of Internet Paths over IPv4 & IPv6 Using NorNet Core Infrastructure Forough Golkar foroughg@ifi.uio.no Master’s Thesis Spring 2014 Measuring and Comparing the Stability of Internet Paths over IPv4 & IPv6 Forough Golkar foroughg@ifi.uio.no 16th June 2014 Dedicated to my lovely mother, Fariba ii Abstract Enormous Internet growth is an obvious trend nowadays while Internet protocol version 4 address space exhaustion led into the invention of Inter- net protocol version 6 and subsequently raised the transitioning challenges from one protocol to the other one. As the Internet protocol version 6 have not been around for a long time, thus there is a limitation knowledge in topology, routing change and performance of IPv6. Several studies are go- ing on in order to getting the information about IPv6 which makes a con- tribution with improvement and deployment of IPv6 and accelerates this transitioning which one of the aspects is the Internet path stability. With this aid this thesis proposed a comparative study of Internet path stability over IPv4 and IPv6. First a measurement of Internet paths over both IP versions has been performed, then the Internet path changes have been extracted in each single set of source-destination pairs. Finally some analysis on the data has been performed in order to observe the stability of Internet paths and provided a comparative study in the set of IPv4 and IPv6. iii iv Acknowledgement I would like to express my appreciation to the following persons for their kind supports during this thesis: • My sincere gratitude to Amund Kvalbein, for accepting supervising me. -
4 ICMP, Fragmentation, Ipv6, DHCP, NAT.Pptx
1/19/11 DNS Caching DNS Name Resolution Exercises Show the DNS resolution paths, assuming the DNS hierarchy shown in the figures and assuming caching: • Once a (any) name server learns mapping, it caches mapping • thumper.cisco.com looks up bas.cs.princeton.edu • to reduce latency in DNS translation • thumper.cisco.com looks up opt.cs.princeton.edu • Cache entries timeout (disappear) after some time (TTL) • thumper.cisco.com looks up cat.ee.princeton.edu • TTL assigned by the authoritative server responsible for the host name • thumper.cisco.com looks up ket.physics.princeton.edu • Local name servers typically also cache • bas.cs.princeton.edu looks up dog.ee.princeton.edu • TLD name servers to reduce visits to root name servers • opt.cs.princeton.edu looks up cat.ee.princeton.edu • all other name server referrals • both positive and negative results 1 2 Peterson & Davie 2nd. ed., pp. 627, 628 DNS Design Points DNS Design Points DNS serves a core Internet function application application At which protocol layer does the DNS operate? transport •host, routers, and name servers communicate to " transport resolve names (name to address translation) DNS serves a core Internet function •complexity at network’s “edge” At which protocol layer does the DNS operate? network network •host, routers, and name servers communicate to " resolve names (name to address translation) link Why not centralize DNS? link •complexity at network’s “edge” •single point of failure physical •traffic volume physical •performance: distant centralized database Why not centralize DNS? •maintenance ➡doesn’t scale! DNS is “exploited” for server load balancing, how? 3 4 1 1/19/11 DNS protocol, messages DNS protocol, messages DNS protocol : query and reply messages, both with same message format Name, type fields for a query msg header . -
15-441 Computer Networking Outline IP Service Model Ipv4 Header Fields
Outline • The IP protocol 15-441 15-441 Computer Networking • IPv4 15-641 • IPv6 Lecture 6 – The Internet Protocol • IP in practice Peter Steenkiste • Network address translation • Address resolution protocol • Tunnels Fall 2016 www.cs.cmu.edu/~prs/15-441-F16 2 IP Service Model IPv4 Header Fields • Low-level communication model provided by Internet 3 • Version: IP Version 0481216192428 ver- 1 HLe sio TOS Length • Datagram n n Fl Identifier ag Offset • 4 for IPv4 s • Each packet self-contained TTL Protocol Checksum • All information needed to get to destination Source Address • HLen: Header Length Destination Address • No advance setup or connection maintenance Options (if any) • 32-bit words (typically 5) Data • Analogous to letter or telegram • TOS: Type of Service 0 4 8 121619242831 • Priority information version HLen TOS Length • Length: Packet Length IPv4 Identifier Flag Offset • Bytes (including header) Packet TTL Protocol Checksum Header Format • Header format can change with versions Source Address • First byte identifies version Destination Address • Length field limits packets to 65,535 bytes Options (if any) • In practice, break into much smaller packets for network performance considerations Data 3 4 1 IPv4 Header Fields IP Delivery Model • Identifier, flags, fragment offset used for fragmentation • Best effort service • Time to live • Must be decremented at each router • Network will do its best to get packet to destination • Packets with TTL=0 are thrown away • Does NOT guarantee: • Ensure packets exit the network 3 0 4