TCP/IP
`itustrated.
`
`
`
`Q
`
`EXHIBIT 1019 - PAGE 0001
`The P
`
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`WN
`
`IPR2022-01227
`IPR2022-01227
`EXHIBIT 1019 - PAGE 0001
`
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`
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`WN
`‘arers
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`
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`lame
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`Sa: a i
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`N2 8 a
`
`

`

`TCP/IP illustrated, Volume 1
`
`The Protocols
`
`W. Richard Stevens
`
`A
`vv
`
`ADDISON-WESLEY PUBLISHING COMPANY
`Reading, Massachusetts Menlo Park, California New York
`Don Mills, Ontario Wokingham, England Amsterdam
`Bonn Sydney Singapore Tokyo Madrid San Juan
`Seoul Milan Mexico City Taipei
`
`IPR2022-01227
`IPR2022-01227
`EXHIBIT 1019 - PAGE 0002
`EXHIBIT 1019 - PAGE 0002
`
`

`

`UNIXis a technology trademark of X/Open Company, Ltd.
`
`The publisher offers discounts on this book when ordered in quantity for specialsales.
`For more information please contact:
`Corporate & Professional Publishing Group
`Addison-Wesley Publishing Company
`One Jacob Way
`Reading, Massachusetts 01867
`
`Library of Congress Cataloging-in-Publication Data
`Stevens, W. Richard
`TCP/IP Illustrated: the protocols/W. Richard Stevens.
`p. cm. — (Addison-Wesley professional computingseries)
`Includes bibliographical references and index.
`ISBN 0-201-63346-9 (v. 1)
`1.TCP/IP (Computer network protocol)I. Title. IT. Series.
`TK5105.55S74 1994
`004.6°2—dc20
`
`Copyright © 1994 by Addison-Wesley Publishing Company,Inc.
`
`All rights reserved. No part of this publication may be reproduced,stored in a retrieval
`system, or transmitted, in any form, or by any means,electronic, mechanical, photocopying,
`recording, or otherwise, without the prior written consent of the publisher. Printed in the
`United States of America. Published simultaneously in Canada.
`
`Text printed on recycled and acid-free paper
`
`ISBN 0-201-63346-9
`7891011 12 13 14 15-MA-99989796
`Seventh printing, March 1996
`
`IPR2022-01227
`IPR2022-01227
`EXHIBIT 1019 - PAGE 0003
`EXHIBIT 1019 - PAGE 0003
`
`

`

`TCP/IP Illustrated, Volume 1
`
`IPR2022-01227
`IPR2022-01227
`EXHIBIT 1019 - PAGE 0004
`EXHIBIT 1019 - PAGE 0004
`
`

`

`Addison-Wesley Professional Computing Series
`
`Brian W. Kernighan, Consulting Editor
`
`Ken Arnold/John Peyton, A C User’s Guide to ANSI C
`Tom Cargill, C++ Programming Style
`William R. Cheswick/Steven M.Bellovin, Firewalls and Internet Security: Repelling the Wily Hacker
`David A. Curry, UNIX® System Security: A Guidefor Users and System Administrators
`Erich Gamma/Richard Helm/Ralph Johnson/John Vlissides, Design Patterns: Elements of Reusable
`Object-Oriented Software
`John Lakos, Large-Scale C++ Software Design
`Scott Meyers, Effective C++: 50 Specific Ways to Improve Your Programs and Designs
`Scott Meyers, More Effective C++: 35 New Ways to Improve Your Programs and Designs
`Robert B. Murray, C++ Strategies and Tactics
`David R. Musser/Atul Saini, STL Tutorial and Reference Guide: C++ Programming with the Standard
`Template Library
`John K. Ousterhout, Tel and the Tk Toolkit
`Craig Partridge, Gigabit Networking
`J. Stephen PendergrastJr., Desktop KornShell Graphical Programming
`Radia Perlman,Interconnections: Bridges and Routers
`David M.Piscitello/A. Lyman Chapin, Open Systems Networking: TCP/IP and OSI
`Stephen A. Rago, UNIX® System V Network Programming
`Curt Schimmel, UNIX® Systems for Modern Architectures: Symmetric Multiprocessing and
`Cachingfor Kernel Programmers
`W.Richard Stevens, Advanced Programming in the UNIX® Environment
`W.Richard Stevens, TCP/IP Illustrated, Volume 1: The Protocols
`W.Richard Stevens, TCP/IP Illustrated, Volume 3: TCPfor Transactions, HTTP, NNTP,andthe
`UNIX Domain Protocols
`Gary R. Wright/W.Richard Stevens, TCP/IP Illustrated, Volume 2: The Implementation
`
`IPR2022-01227
`IPR2022-01227
`EXHIBIT 1019 - PAGE 0005
`EXHIBIT 1019 - PAGE 0005
`
`

`

`To Brian Kernighan and John Wait,
`for their encouragement,faith, and support
`over the past 5 years.
`
`IPR2022-01227
`IPR2022-01227
`EXHIBIT 1019 - PAGE 0006
`EXHIBIT 1019 - PAGE 0006
`
`

`

`Praise for TCP/IP Illustrated, Volume 1: The Protocols
`
`“This is sure to be the bible for TCP/IP developers and users. Within minutesof picking upthetext,
`I encountered several scenarios which had tripped-up both my colleagues and myself inthe past.
`Stevens reveals many of the mysteries once held tightly by the ever-elusive networking gurus.
`Having been involved in the implementation of TCP/IP for some years now,I consider this by far
`the finest text to date.”
`
`— Robert A. Ciampa, Network Engineer, Synemetics, division of 3COM
`
`“While all of Stevens’ books are readable and technically excellent, this new opus is awesome.
`Although manybooks describe the TCP/IP protocols, Stevens provides a level of depth and real-
`world detail lacking from the competition. He puts the reader inside TCP/IP using a visual approach
`and showsthe protocols in action.”
`
`— Steven Baker, Networking Columnist, Unix Review
`
`“TCPIHP Illustrated, Volume 1 is an excellent reference for developers, network administrators, or
`anyone who needsto understand TCP/IP technology. TCP/IP Illustrated is comprehensive in its
`coverage of TCP/IP topics, providing enoughdetails to satisfy the experts while giving enough
`background and commentary for the novice.”
`
`— BobWilliams, V.P. Marketing, NetManage,Inc.
`
`*,.. the difference is that Stevens wants to show as wellas tell about the protocols. His principal
`teaching tools are straight-forward explanations, exercises at the ends of chapters, byte-by-byte
`diagrams of headers andthe like, and listings of actual traffic as examples.”
`
`— Walter Zintz, UnixWorld
`
`“Muchbetter than theory only ... W. Richard Stevens takes a multihost-based configuration and uses
`it as a travelogue of TCP/IP exampleswithillustrations. TCP/IP Illustrated, Volume I is based on
`practical examplesthat reinforce the theory — distinguishing this book from others on the subject,
`and making it both readable and informative.”
`
`— Peter M. Haverlock, Consultant, IBM TCP/IP Development
`
`“The diagramshe uses are excellent and his writing style is clear and readable. In sum, Stevens has
`made a complex topic easy to understand. This book merits everyone’s attention. Please read it and
`keep it on your bookshelf.”
`— Elizabeth Zinkann, Sys Admin
`
`“W. Richard Stevens has produceda fine text and reference work.It is well organized and very
`clearly written with, as the title suggests, many excellentillustrations exposing the intimate details
`of the logic and operation of IP, TCP, and the supporting cast of protocols and applications.”
`
`— Scott Bradner, Consultant, Harvard University OIT/NSD
`IPR2022-01227
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`EXHIBIT 1019 - PAGE 0007
`
`

`

`Contents
`
`Preface
`
`XV
`
`Chapter 1
`
`Introduction
`
`1.1
`1.2
`1.3
`1.4
`1.5
`1.6
`1.7
`1.8
`1.9
`1.10
`1.11
`1.12
`1.13
`1.14
`1.15
`1.16
`1.17
`
`1
`
`6
`
`12
`
`9
`
`14
`
`15
`
`Introduction
`1
`Layering
`TCP/IP Layering
`7
`Internet Addresses
`The Domain Name System
`Encapsulation
`9
`Demultiplexing
`11
`Client-Server Model
`Port Numbers
`12
`Standardization Process
`RFCs
`14
`Standard, Simple Services
`The Internet
`16
`16
`Implementations
`Application Programming Interfaces
`Test Network
`18
`Summary
`
`19
`
`17
`
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`
`Vii
`
`

`

`Contents
`
`21
`
`33
`
`viii
`
`TCP/IP Illustrated
`
`Chapter 2.
`
`Link Layer
`
`21
`Introduction
`Ethernet and IEEE 802 Encapsulation
`Trailer Encapsulation
`23
`SLIP: Serial Line IP
`24
`25
`Compressed SLIP
`PPP: Point-to-Point Protocol
`Loopback Interface
`28
`MTU
`29
`30
`Path MTU
`Serial Line Throughput Calculations
`Summary
`31
`
`26
`
`21
`
`30
`
`IP: Internet Protocol
`
`42
`
`33
`Introduction
`34
`IP Header
`37
`IP Routing
`Subnet Addressing
`Subnet Mask
`43
`Special Case IP Addresses
`A Subnet Example
`46
`ifconfig Command
`47
`netstat Command
`49
`IP Futures
`49
`Summary
`50
`
`45
`
`ARP: Address Resolution Protocol
`
`53
`
`53
`Introduction
`54
`An Example
`56
`ARP Cache
`ARP Packet Format
`ARP Examples
`57
`Proxy ARP
`Gratuitous ARP
`arp Command
`Summary
`63
`
`60
`
`62
`63
`
`56
`
`RARP: Reverse Address Resolution Protocol
`
`65
`
`65
`Introduction
`RARP Packet Format
`RARP Examples
`66
`RARP Server Design
`Summary
`68
`
`65
`
`67
`
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`

`

`TCP/IP Illustrated
`
`Contents
`
`ix
`
`Chapter 6.
`
`ICMP: Internet Control Message Protocol
`
`69
`
`69
`Introduction
`70
`ICMP Message Types
`ICMP Address Mask Request and Reply
`ICMP Timestamp Request and Reply
`ICMP Port Unreachable Error
`77
`4.4BSD Processing of
`ICMP Messages
`Summary
`83
`
`72
`
`74
`
`81
`
`Ping Program
`
`85
`
`Introduction
`85
`Ping Program
`IP Record Route Option
`IP Timestamp Option
`Summary
`96
`
`91
`
`95
`
`Traceroute Program
`
`97
`Introduction
`Traceroute Program Operation
`LAN Output
`99
`WAN Output
`102
`IP Source Routing Option
`Summary
`109
`
`97
`
`104
`
`IP Routing
`
`111
`Introduction
`112
`Routing Principles
`ICMP Host and Network Unreachable Errors
`To Forward or Not
`to Forward
`119
`ICMP Redirect Errors
`119
`ICMP Router Discovery Messages
`Summary
`125
`
`123
`
`117
`
`85
`
`97
`
`111
`
`Chapter 10.
`
`Dynamic Routing Protocols
`
`127
`
`10.1
`10.2
`10.3
`10.4
`10.5
`10.6
`10.7
`10.8
`10.9
`
`127
`Introduction
`127
`Dynamic Routing
`128
`Unix Routing Daemons
`RIP: Routing Information Protocol
`RIP Version 2
`136
`137
`OSPF: Open Shortest Path First
`138
`BGP: Border Gateway Protocol
`CIDR: Classless Interdomain Routing
`Summary
`141
`
`129
`
`140
`
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`

`

`x
`
`TCP/IP Illustrated
`
`Chapter 11.
`
`UDP: User Datagram Protocol
`
`11.1
`11.2
`11.3
`11.4
`
`143
`Introduction
`144
`UDP Header
`144
`UDP Checksum
`147
`A Simple Example
`148
`IP Fragmentation
`ICMP Unreachable Error (Fragmentation Required)
`Determining the Path MTU Using Traceroute
`153
`Path MTU Discovery with UDP
`155
`Interaction Between UDP and ARP
`Maximum UDP Datagram Size
`ICMP Source Quench Error
`UDP Server Design
`162
`Summary
`167
`
`159
`160
`
`157
`
`Contents
`
`143
`
`151
`
`Broadcasting and Multicasting
`
`169
`
`169
`Introduction
`171
`Broadcasting
`Broadcasting Examples
`Multicasting
`175
`Summary
`178
`
`172
`
`IGMP: Internet Group Management Protocol
`
`179
`
`179
`Introduction
`IGMP Message
`IGMP Protocol
`An Example
`Summary
`
`180
`180
`183
`186
`
`—> Chapter 14.
`
`DNS: The Domain Name System
`
`187
`
`14.1
`14.2
`14.3
`14.4
`14.5
`14.6
`14.7
`14.8
`14.9
`14.10
`
`187
`Introduction
`188
`DNS Basics
`DNS Message Format
`A Simple Example
`Pointer Queries
`Resource Records
`Caching
`203
`UDP or TCP
`Another Example
`Summary
`208
`
`191
`
`194
`
`198
`201
`
`206
`
`206
`
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`

`

`TCP/IP Illustrated
`
`Contents
`
`xi
`
`~~+ Chapter 15.
`
`TFTP: Trivial File Transfer Protocol
`
`209
`
`introduction
`Protocol
`An Example
`Security
`Summary
`
`209
`209
`
`211
`
`213
`213
`
`BOOTP: Bootstrap Protocol
`Introduction
`215
`BOOTP Packet Format
`An Example
`218
`BOOTP Server Design
`BOOTP Through a Router
`Vendor-Specific Information
`Summary
`222
`
`215
`
`219
`
`215
`
`220
`221
`
`Chapter 17.
`
`TCP: Transmission Control Protocol
`
`223
`
`17.1
`17.2
`17.3
`17.4
`
`Introduction
`TCP Services
`TCP Header
`Summary
`
`223
`223
`225
`227
`
`Chapter 18.
`
`TCP Connection Establishment and Termination
`
`229
`
`229
`
`18.1
`18.2
`18.3
`18.4
`18.5
`18.6
`18.7
`18.8
`18.9
`18.10
`18.11
`18.12
`
`229
`Introduction
`Connection Establishment and Termination
`Timeout of Connection Establishment
`235
`Maximum Segment Size
`236
`TCP Half-Close
`238
`TCP State Transition Diagram
`Reset Segments
`246
`Simultaneous Open
`250
`Simultaneous Close
`252
`TCP Options
`253
`TCP Server Design
`Summary
`260
`
`254
`
`240
`
`Chapter 19.
`
`TCP Interactive Data Flow
`
`263
`
`263
`
`Introduction
`263
`Interactive Input
`Delayed Acknowledgments
`Nagle Algorithm
`267
`Window Size Advertisements
`Summary
`274
`
`265
`
`274
`
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`
`

`

`xii
`
`TCP/IP Illustrated
`
`Chapter 20.
`
`TCP Bulk Data Flow
`
`275
`Introduction
`275
`Normal Data Flow
`280
`Sliding Windows
`282
`Window Size
`284
`PUSH Flag
`285
`Slow Start
`Bulk Data Throughput
`Urgent Mode
`292
`Summary
`
`296
`
`286
`
`20.9
`
`Contents
`
`275
`
`Chapter 21.
`
`TCP Timeout and Retransmission
`
`297
`
`21.1
`21.2
`
`297
`Introduction
`Simple Timeout and Retransmission Example
`Round-Trip Time Measurement
`299
`_ An RTT Example
`301
`Congestion Example
`306
`310
`Congestion Avoidance Algorithm
`Fast Retransmit and Fast Recovery Algorithms
`Congestion Example (Continued)
`313
`Per-Route Metrics
`316
`ICMP Errors
`317
`Repacketization
`320
`Summary
`321
`
`298
`
`312
`
`Chapter 22.
`
`TCP Persist Timer
`
`22.1
`22.2
`22.3
`22.4
`
`323
`Introduction
`323
`An Example
`Silly Window Syndrome
`Summary
`330
`
`325
`
`Chapter 23.
`
`TCP Keepalive Timer
`
`23.1
`23.2
`23.3
`23.4
`
`331
`Introduction
`332
`Description
`Keepalive Examples
`Summary
`337
`
`333
`
`Chapter 24.
`
`TCP Futures and Performance
`
`24.1
`24.2
`24.3
`24.4
`
`339
`Introduction
`Path MTU Discovery
`Long Fat Pipes
`344
`Window Scale Option
`
`340
`
`347
`
`323
`
`331
`
`339
`
`IPR2022-01227
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`EXHIBIT 1019 - PAGE 0013
`
`

`

`TCP/IP [llustrated
`
`Contents
`
`xiii
`
`24.5
`24.6
`24.7
`24.8
`24.9
`
`349
`Timestamp Option
`PAWS: Protection Against Wrapped Sequence Numbers 351
`T/TCP: A TCP Extension for Transactions
`351
`TCP Performance
`354
`Summary
`356
`
`SNMP: Simple Network Management Protocol
`359
`—>Chapter 25.
`
`25.1
`25.2
`25.3
`25.4
`25.5
`25.6
`25.7
`25.8
`25.9
`25.10
`25.11
`25.12
`25.13
`
`359
`Introduction
`360
`Protocol
`Structure of Management Information
`Object Identifiers
`364
`Introduction to the Management Information Base
`instance Identification
`367
`370
`Simple Examples
`Management Information Base (Continued)
`Additional Examples
`382
`Traps
`385
`ASN.1 and BER
`SNMP Version 2
`Summary
`388
`
`365
`
`372
`
`363
`
`386
`387
`
`—= Chapter 26.
`
`Telnet and Rlogin: Remote Login
`
`389
`
`389
`
`Introduction
`Rlogin Protocol
`Rlogin Examples
`Telnet Protocol
`Telnet Examples
`Summary
`417
`
`391
`396
`401
`406
`
`~—>Chapter 27.
`FTP: File Transfer Protocol
`419
`
`27.1
`27.2
`27.3
`27.4
`
`Introduction
`FTP Protocol
`FTP Examples
`Summary
`439
`
`419
`419
`426
`
`~—+ Chapter 28.
`
`SMTP: Simple Mail Transfer Protocol
`
`441
`
`28.14
`28.2
`28.3
`28.4
`28.5
`
`441
`
`Introduction
`SMTP Protocol
`SMTP Examples
`SMTP Futures
`Summary
`459
`
`442
`448
`452
`
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`EXHIBIT 1019 - PAGE 0014
`
`

`

`xiv
`
`TCP/IP Mustrated
`
`—> Chapter 29.
`29.1
`29.2
`29.3
`
`NFS: Network File System
`
`461
`Introduction
`461
`Sun Remote Procedure Call
`XDR: External Data Representation
`Port Mapper
`465
`NFS Protocol
`467
`NFS Examples
`474
`NFS Version 3
`479
`Summary
`480
`
`465
`
`Chapter 30.
`
`Other TCP/IP Applications
`
`30.1
`30.2
`30.3
`30.4
`30.5
`30.6
`
`481
`
`Introduction
`481
`Finger Protocol
`483
`Whois Protocol
`Archie, WAIS, Gopher, Veronica, and WWW
`X Window System
`486
`Summary
`490
`
`484
`
`Appendix A.
`
`The tcpdump Program
`
`491
`BSD Packet Filter
`493
`SunOS Network Interface Tap
`SVR4 Data Link Provider Interface
`tepdump Output
`495
`Security Considerations
`Socket Debug Option
`
`496
`496
`
`494
`
`Appendix B.
`
`Computer Clocks
`
`Appendix C.
`
`The sock Program
`
`Appendix D.
`
`Solutions to Selected Exercises
`
`Appendix E.
`
`Configurable Options
`
`BSD/386 Version 1.0
`SunOS 4.1.3
`527
`System V Release 4
`Solaris 2.2
`529
`AIX 3.2.2
`536
`4.4BSD
`537
`
`526
`
`529
`
`Appendix F.
`
`Source Code Availability
`
`Bibliography
`
`Index
`
`Contents
`
`461
`
`481
`
`491
`
`499
`
`503
`
`507
`
`525
`
`539
`
`543
`
`555
`
`IPR2022-01227
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`EXHIBIT 1019 - PAGE 0015
`
`

`

`Preface
`
`Introduction
`
`This book describes the TCP/IP protocol suite, but from a different perspective than
`other texts on TCP/IP. Instead of just describing the protocols and what they do, we'll
`use a popular diagnostic tool to watch the protocols in action. Seeing how the protocols
`operate in varying circumstances provides a greater understanding of how they work
`and why certain design decisions were made. It also provides a look into the imple-
`mentation of the protocols, without having to wade through thousands of lines of
`source code.
`Whennetworking protocols were being developed in the 1960s through the 1980s,
`expensive, dedicated hardware wasrequired to see the packets going “across the wire.”
`Extremefamiliarity with the protocols was also required to comprehendthe packets dis-
`played by the hardware. Functionality of the hardware analyzers was limited to that
`built in by the hardware designers.
`Today this has changed dramatically with the ability of the ubiquitous workstation
`to monitor a local area network [Mogul 1990]. Just attach a workstation to your net-
`work, run some publicly available software (described in Appendix A), and watch what
`goes by on the wire. While many people consider this a tool to be used for diagnosing
`network problems,it is also a powerful tool for understanding how the network proto-
`cols operate, which is the goal of this book.
`This book is intended for anyone wishing to understand how the TCP/IP protocols
`operate: programmerswriting network applications, system administrators responsible
`for maintaining computer systems and networks utilizing TCP/IP, and users who deal
`with TCP/IP applications on a daily basis.
`
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`EXHIBIT 1019 - PAGE 0016
`EXHIBIT 1019 - PAGE 0016
`
`

`

`xvi
`
`TCP/IP Illustrated
`
`Preface
`
`Organization of the Book
`
`The following figure shows the various protocols and applications that are covered.
`The italic number by each box indicates the chapter in which that protocol or applica-
`tion is described.
`
`Chap.7
`27
`28
`25
`29
`
`
`
`Ping Erp||sme||x=||B®||pns||Tere||BOOTP |_NFS|||TelRet&!)
`Rlogin route|RPC|
`
`
`26
`
`30
`
`8
`
`14
`
`15
`
`G
`
`
`
`TCP 101,22,23,24|UDP|
`
`17, 18, 19, 20
`
`11,12
`
`4
`
`a
`
`2| Data
`
`RAR?
`
`5
`
`media
`
`(Numerous fine points are missing from this figure that will be discussed in the appro-
`priate chapter. For example, both the DNS and RPC use TCP, which we don’t show.)
`We take a bottom-up approach to the TCP/IP protocol suite. After providing a
`basic introduction to TCP/IP in Chapter 1, we will start at the link layer in Chapter 2
`and work our way up the protocol stack. This provides the required background for
`later chapters for readers whoaren’t familiar with TCP/IP or networking in general.
`This book also uses a functional approach instead of following a strict bottom-to-
`top order. For example, Chapter 3 describes the IP layer and the IP header. But there
`are numerous fields in the IP headerthat are best described in the context of an applica-
`tion that uses or is affected by a particular field. Fragmentation, for example, is best
`understood in terms of UDP (Chapter11), the protocol often affected by it. The time-to-
`live field is fully described when we look at the Traceroute program in Chapter 8,
`because this field is the basis for the operation of the program. Similarly, many features
`of ICMP are described in the later chapters, in terms of how a particular ICMP message
`is used by a protocolor an application.
`Wealso don’t wantto saveall the good stuff until the end, so we describe TCP/IP
`applications as soon as wehave the foundation to understand them. Ping and Trace-
`route are described after IP and ICMP have been discussed. The applications built on
`UDP (multicasting, the DNS, TFTP, and BOOTP) are described after UDP has been
`
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`

`TCP/IP Illustrated
`
`Preface
`
`xvii
`
`examined. The TCP applications, however, along with network management, must be
`saved until the end, after we’ve thoroughly described TCP. This text focuses on how
`these applications use the TCP/IP protocols. We do not provideall the details on run-
`ning these applications.
`
`Readers
`
`This book is self-contained and assumes no specific knowledge of networking or
`TCP/IP. Numerous references are provided for readers interested in additional details
`on specific topics.
`This book can be used in many ways. It can be used as a self-study reference and
`covered from start to finish by someoneinterested in all the details on the TCP/IP
`protocol suite. Readers with some TCP/IP background might want to skip ahead and
`start with Chapter 7, and then focus on the specific chapters in which they’re interested.
`Exercises are provided at the end of the chapters, and most solutions are in Appen-
`dix D. This is to maximize the usefulnessof the text as a self-study reference.
`Whenusedas part of a one- or two-semester course in computer networking, the
`focus should be on IP (Chapters 3 and 9), UDP (Chapter 11), and TCP (Chapters 17-24),
`along with someof the application chapters.
`Many forward and backward references are provided throughout the text, along
`with a thorough index, to allow individual chapters to be studied by themselves.Alist
`of all the acronyms used throughoutthe text, along with the compoundterm for the
`acronym, appears on the inside back covers.
`If you have access to a network you are encouraged to obtain the software used in
`this book (Appendix F) and experiment on your own. Hands-on experimentation with
`the protocols will provide the greatest knowledge (and makeit more fun).
`
`Systems Used for Testing
`
`Every example in the book was run on an actual network and the resulting output
`savedinafile for inclusion in the text. Figure 1.11 (p. 18) shows a diagram ofthe differ-
`ent hosts, routers, and networks that are used.
`(This figure is also duplicated on the
`inside front cover for easy reference while reading the book.) This collection of net-
`works is simple enough that the topology doesn’t confuse the examples, and with four
`systems acting as routers, we can see the error messages generated by routers.
`Most of the systems have a namethat indicates the type of software being used:
`bsdi, svr4, sun, solaris, aix, slip, and so on. In this way wecan identify the type
`of software that we're dealing with by looking at the system namein the printed output.
`A wide rangeof different operating systems and TCP/IP implementations are used:
`
`¢ BSD/386 Version 1.0 from Berkeley Software Design, Inc., on the hosts named
`bsdi and slip. This system is derived from the BSD Networking Software,
`Release 2.0.
`(We show thelineage of the various BSD releases in Figure 1.10 on
`p. 17.)
`
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`

`

`xviii
`
`TCP/IP Illustrated
`
`Preface
`
`¢ Unix System V/386 Release 4.0 Version 2.0 from U.H. Corporation, on the host
`named svr4. This is vanilla SVR4 and contains the standard implementation of
`TCP/IP from Lachman Associates used with most versions of SVR4.
`
`e¢ SunOS 4.1.3 from Sun Microsystems, on the host named sun. The SunOS4.1.x
`systems are probably the most widely used TCP/IP implementations. The
`TCP/IP codeis derived from 4.2BSD and 4.3BSD.
`
`¢ Solaris 2.2 from Sun Microsystems, on the host named solaris. TheSolaris 2.x
`systems havea different implementation of TCP/IP from the earlier SunOS4.1.x
`systems, and from SVR4. (This operating system is really SunOS 5.2, but is com-
`monly called Solaris 2.2.)
`
`¢ AIX 3.2.2 from IBM on the host named aix. The TCP/IP implementation is
`based on the 4.3BSD Renorelease.
`
`¢
`
`4.4BSD from the Computer Systems Research Group at the University of Califor-
`nia at Berkeley, on the host vangogh.cs.berkeley.edu. This system has the
`latest release of TCP/IP from Berkeley. (This system isn’t shown in the figure on
`the inside front cover, but is reachable across the Internet.)
`
`Although these are all Unix systems, TCP/IP is operating system independent, andis
`available on almost every popular non-Unix system. Most of this text also applies to
`these non-Unix implementations, although some programs (such as Traceroute) may
`not be providedonall systems.
`
`Typographical Conventions
`
`When wedisplay interactive input and output we’ll show our typed input in a bold
`font, and the computer output like this. Comments are addedinitalics.
`
`bsdi % telnet svr4 discard
`Trying 140.252.13.34...
`Connected to svr4.
`
`connect to the discard server
`this line and next output by Telnet client
`
`Also, we always include the name of the system as part of the shell prompt (bsdi in
`this example) to show on which host the commandwasrun.
`
`Throughout the text we'll use indented, parenthetical notes such as this to describe historical
`points or implementation details.
`
`We sometimesrefer to the complete description of a commandin the Unix manual
`as in ifconfig(8). This notation, the name of the command followed by a numberin
`parentheses, is the normal way of referring to Unix commands. The numberin paren-
`theses is the section number in the Unix manual of the “manual page” for the com-
`mand, where additional information can be located. Unfortunately not all Unix systems
`organize their manuals the same, with regard to the section numbers used for various
`groupings of commands. We'll use the BSD-style section numbers (which is the same
`for BSD-derived systems such as SunOS4.1.3), but your manuals may be organized
`differently.
`
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`

`

`TCP/IP Illustrated
`
`Acknowledgments
`
`Preface
`
`xix
`
`Although the author’s nameis the only one to appear on the cover, the combinedeffort
`of many people is required to produce a quality text book. First and foremost is the
`author’s family, who put up with the long and weird hours that go into writing a book.
`Thank you once again, Sally, Bill, Ellen, and David.
`The consulting editor, Brian Kernighan, is undoubtedly the best in the business. He
`wasthefirst one to read various drafts of the manuscript and mark it up with his infi-
`nite supply of red pens. His attention to detail, his continual prodding for readable
`prose, and his thorough reviewsof the manuscript are an immenseresourceto a writer.
`Technical reviewers provide a different point of view and keep the author honest by
`catching technical mistakes. Their comments, suggestions, and (most importantly)criti-
`cisms add greatly to the final product. My thanks to Steve Bellovin, Jon Crowcroft, Pete
`Haverlock, and Doug Schmidt for comments on the entire manuscript. Equally valu-
`able comments were provided on portions of the manuscript by Dave Borman, Tony
`DeSimone, Bob Gilligan, Jeff Gitlin, John Gulbenkian, Tom Herbert, Mukesh Kacker,
`Barry Margolin, Paul Mockapetris, Burr Nelson, Steve Rago, James Risner, Chris
`Walquist, Phil Winterbottom, and Gary Wright. A special thanks to Dave Borman for
`his thorough review of all the TCP chapters, and to Bob Gilligan who should be listed as
`a coauthor for Appendix E.
`An author cannot workin isolation, so I would like to thank the following persons
`for lots of small favors, especially by answering my numerous e-mail questions: Joe
`Godsil, Jim Hogue, Mike Karels, Paul Lucchina, Craig Partridge, Thomas Skibo, and
`Jerry Toporek.
`This book is the result of my being asked lots of questions on TCP/IP for which I
`could find no quick, immediate answer. It was then that I realized that the easiest way
`to obtain the answers was to run smalltests, forcing certain conditions to occur, and just
`watch what happens.
`I thank Pete Haverlock for asking the probing questions and Van
`Jacobson for providing so much of the publicly available software that is used in this
`book to answerthe questions.
`A book on networking needs a real network to work with along with access to the
`Internet. My thanks to the National Optical Astronomy Observatories (NOAO), espe-
`cially Sidney Wolff, Richard Wolff, and Steve Grandi, for providing access to their net-
`works and hosts. A special thanks to Steve Grandi for answering lots of questions and
`' providing accounts on various hosts. My thanks also to Keith Bostic and Kirk McKu-
`sick at the U.C. Berkeley CSRGfor accessto thelatest 4.4BSD system.
`Finally, it is the publisher that pulls everything together and does whatever is
`required to deliver the final product to the readers. This all revolves around the editor,
`and John Wait is simply the best there is. Working with John andtherest of the profes-
`sionals at Addison-Wesley is a pleasure. Their professionalism and attention to detail
`showin the end result.
`Camera-ready copy of the book was produced by the author, a Troff die-hard, using
`the Groff package written by James Clark.
`I welcomeelectronic mail from any readers
`with comments, suggestions, or bugfixes.
`Tucson, Arizona
`October 1993
`
`W.Richard Stevens
`rstevens@noao.edu
`http: //www.noao.edu/~rstevens
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`

`

`Introduction
`
`1.1
`
`introduction
`
`The TCP/IP protocol suite allows computers ofall sizes, from many different computer
`vendors, running totally different operating systems, to communicate with each other.
`It is quite amazing becauseits use has far exceededits original estimates. What started
`in the late 1960s as a government-financed research project into packet switching net-
`works has, in the 1990s, turned into the most widely used form of networking between
`computers. It is truly an open system in that the definition of the protocol suite and
`many of its implementations are publicly available at little or no charge. It forms the
`basis for what is called the worldwide Internet, or the Internet, a wide area network
`(WAN)of more than one million computers thatliterally spans the globe.
`This chapter provides an overview of the TCP/IP protocol suite, to establish an ade-
`quate background for the remaining chapters. For a historical perspective on the early
`developmentof TCP/IP see [Lynch 1993].
`
`1.2
`
`Layering
`
`Networkingprotocols are normally developed in layers, with each layer responsible for a
`different facet of the communications. A protocol suite, such as TCP/IP, is the combina-
`tion of different protocols at various layers. TCP/IP is normally considered to be a
`4-layer system, as shown in Figure 1.1.
`
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`

`2
`
`Introduction
`
`Chapter 1
`
`
`
`
`
`
`
` Telnet, FTP, e-mail, etc.
`
`
`
`device driver and interface card
`
`TCP, UDP
`
`IP, ICMP, IGMP
`
`Figure 1.1 The four layers of the TCP/IP protocolsuite.
`
`Each layer hasa different responsibility.
`
`1. The link layer, sometimescalled the data-link layer or network interface layer, nor-
`mally includes the device driver in the operating system and the corresponding
`network interface card in the computer. Together they handle all the hardware
`details of physically interfacing with the cable (or whatever type of media is
`being used).
`
`. The network layer (sometimes called the internet layer) handles the movement of
`packets around the network. Routing of packets, for example, takes place here.
`IP (Internet Protocol), ICMP (Internet Control Message Protocol), and IGMP
`(Internet Group Management Protocol) provide the network layer in the
`TCP/IP protocolsuite.
`
`. The transport layer provides a flow of data between twohosts, for the applica-
`tion layer above.
`In the TCP/IP protocol suite there are two vastly different
`transport protocols: TCP (Transmission Control Protocol) and UDP (User Data-
`gram Protocol).
`
`TCP provides a reliable flow of data between two hosts. It is concerned with
`things such as dividing the data passedto it from the application into appropri-
`ately sized chunks for the network layer below,-acknowledging received pack-
`ets, setting timeouts to make certain the other end acknowledges packets that
`are sent, and so on. Becausethis reliable flow of data is provided by the trans-
`portlayer, the application layer can ignore all these details.
`
`UDP, on the other hand, provides a much simpler service to the application
`layer. It just sends packets of data called datagrams from one hostto the other,
`but there is no guarantee that the datagramsreach the other end. Any desired
`reliability must be addedbythe application layer.
`Thereis a use for each type of transport protocol, which we’ll see when we look
`at the different applications that use TCP and UDP.
`
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`

`

`Section 1.2
`
`Layering
`
`3
`
`4. The application layer handles the details of the particular application. There are
`many common TCP/IP applications that almost every implementation pro-
`vides:
`
`Telnet for remote login,
`FTP, the File Transfer Protocol,
`SMTP, the Simple Mail Transfer protocol, for electronic mail,
`SNMP, the Simple Network ManagementProtocol,
`
`and many more, some of which wecover in later chapters.
`
`If we have two hosts on a local area network (LAN) such as an Ethernet, both run-
`ning FTP, Figure 1.2 showsthe protocols involved.
`
`application
`
`transport
`
`network
`
`user
`processes
`
`handles
`application
`details
`
`kernel
`
`handles
`communication
`details
`
`link
`
`Ethernet
`driver
`
`Ethernet
`driver
`
`Figure 1.2 Two hosts on a LAN running FTP.
`
`We havelabeled one application box the FTP client and the other the FTP server.
`Most network applications are designed so that one endis the client and the other side
`the server. The server provides sometype of service to clients, in this case accessto files
`on the server host. In the remote login application, Telnet, the service provided to the
`client is the ability to login to the server’s host.
`Each layer has one or more protocols for communicating with its peer at the same
`layer. One protocol, for example, allows the two TCP layers to communicate, and
`anotherprotocollets the two IP layers communicate.
`On the right