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 diagnoshc 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 implementation of the protocols, without having to wade through thousands of lines of source code.

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 diagnoshc 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 implementation of the protocols, without having to wade through thousands of lines of source code.
　　When networking protocols were being developed in the 1960s through the 1980s,expensive, dedicated hardware was required to see the packcts going "across the wire."Extreme familiarity with the protocols was also required to comprehend the packets displayed 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 network, 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 protocols operate, which is the goal of this book.
　　This book is intended for anyone wishing to understand how the TCP/IP protocols operate: programmers writing 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.
　　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 application is described.(Numerous fine points are missing from this figure that will be discussed in theappropriate chapter. For example, both the DNS and RPC use TCP, which we don't show.)
　　We take a bottom-up approach to the TCP/lP protocol suite. After providing a basic introduction to TCP/IP in Chapter 1, we wilI start at the link Iayer in Chapter 2 and work our way up the protocol stack. This provides the required background for later chapters for readers who aren't fami1iar 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 header that 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 (Chapter 11), 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 protocol or an application.
　　We also don't want to save all the good stUff until the end, so we describe TCP/IP
applications as soon as we have the foundation to understand them. Ping and Traceroute 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 examined. The TCP applications, howeveT, 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 provide all the details on running these applications.

Readers
　　This book is sclf-contained and assumes no specific knowledge of networking or TCP/IP Numerous references are provided for readers interestcd in additional details
on specific topics.This book can be used in many ways. It can be uscd ds a self-study reference and covered from start to finish by someone interested in all tl1e 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 Appendix D. This is to maximize the use fu1ness of the text as a self-study reference.
　　When used as 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 (Chapters17-24),along with some of 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. A list of all the acronyms used throughout the text, along with the compound term 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 make it more fun).

Systems Used Testing
　　Every example in the book was run on an actual network and the resulting outputsaved in a file for inclusion in the text. Figure 1.11(p.18) shows a diagram of the different 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 networks 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 name that indicales the type of software being used:bsdi, svr4, sun, solaris, aix, slip, and so on. In this way we can identify the type of software that we're dealing with by looking at the systern name in the printed output,
　　A wide range of 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 s1ip. This system is derived from the BSD Networking Software,Release 2.0. (We show the lineage of the various BSD releases in Figure 1.10 onP.17.)
　　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.
　　SunOS 4.1.3 from Sun Microsystems, on the host named sun. The SunOS 4.1.x systems are probably the most widely used TCP/IP implementations. The TCP/IP code is derived from 4.2BSD and 4.3BSD.
　　Solaris 2.2 from Sun Microsystems, on the host named solarls. The So1aris 2.x systems have a different implementation of TCP/IP from the earlier SunOS 4.1.x systems, and from SVR4. (This operating system is really SunOS 5.2, but is commonly called Solaris 2.2.)
　　AIX 3.2.2 from lBM on the host named aix. The TCP/IP implementation is based on the 4.3BSD Reno release.
　　4.4BSD from the Computer Systems Research Group at the University of California at Berkeley, on the host vangogh. cs. berkeley. edu. This system has the Iatest 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 arc all Unix systems, TCP/IP is operating system independent, and is 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 provided on all systems.

Typographical Conventions
　　When we display interactive input and output we'll show Our typed input in a bold font, and the computer output like this. Comments are added in italics.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 command was run.
　　Throughout the text we'll use indented,parenthetical notes such as this to describe historical points or implementation details.
　　We sometimes refer to the complete description of a command in the Unix manual as in ifconfig(8). This notation, the name of the command followed by a number in parentheses, is the normal way of referring to Unix commands. The number in paren theses is the section number in the Unix manual of the "manual page" for the command, 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 SunOS 4.1.3), but your manuals may be organized differently.

Acknowledgments
　　Although the author's name is the only one to appear on the cover, the combined effort of many people is required to produce a quality text book. First and fOremost is the
author's family who put up with the 1ong 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 was the first one to read various drafts of the manuscript and mark it up with his infini te supply of red pens. His attention to detail, his continual prodding for readable prose, and his thorough reviews of the manuscript are an immense resource to a writet .
　　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 great1y to the final product. My thanks to Steve Bellovin, Jon Crowcroft, Pete Haverlock, and Doug Schmidt for comments on the entire manuscript. Equally valuable 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 work in 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 small tests, forcing certain conditions to occur, and just
watch what happens. I thank Pete HaverIock for asking the probing questions al1d Van Jacobson for providing so much of the publicly avai1able software that is used in this
book to answer the 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), especially Sidney Wolff, Richard Wolff, and Steve Grandi, for providing access to their networks 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 McKusick at the U.C. Berkeley CSRG for access to the latest 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 and the rest of the professio nals at Addison-Wesley is a pleasure. Their professionalism and attention to detail show in 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 welcome electronic mail from any readers with comments, suggestions, or bug fixes.

Tucson, Arizona
October 1993
W. Richard Stevens
rstevens@noao. edu
http: //www. noao. edu / ~rstevens

(美)W.Richard Stevens：W.Richard Stevens: W. Richard Stevens (1951~1999) 是一位非常受人尊敬的专家，除了《TCP/IP详解》三卷本外，他还有其他两部最为畅销的作品：《UNIX环境高级编程》和《UNIX网络编程》(两卷本)。

Chapter 1. Introduction
1.1 Introduction
1.2 Layering
1.3 TCP/IP Layering
1.4 lnternet 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 lntroduction
2.2 Ethernet and IEEE 802 EncapsuIation
2.3 Trailer Encapsulation
2.4 SLlP: Serial Line IP
2.5 Compressed SLIP
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 Addfesses
3.7 A Subnet Example
3.8 Ifconfiq 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 tntroduction
5.2 RARP Packet Format
5.3 RARP Examples
5.4 RARP Server Design
5.5 Summary
Chapter 6. ICMP: Internet Control Message Protocol
6.1 Introduction
6.2 ICMP Message Types
6.3 ICMP Address Mask Request and Reply
6.4 ICMP Timestamp Request and Reply
6.5 ICMP Port Unreachable Error
6.6 4.4BSD Processing of ICMP Messages
6.7 Summary
Chapter 7. Ping Program
7.1 Introduction
7.2 Ping Program
7.3 IP Record Route Option
7.4 IP Timestamp Option
7.5 Summary
Chapter 8. Traceroute Program
8.1 Introduction
8.2 Traceroute Program Operation
8.3 LAN Output
8.4 WAN Output
8.5 IP Source Routing Option
8.6 Summary
Chapter 9. IP Routing
9.1 Introduction
9.2 Routing Prlnciples
9.3 ICMP Host and Network UnreachabIe Errors
9.4 To Forward or Not to Forward
9.5 ICMP Redirect Errors
9.6 ICMP Router Discovery Messages
9.7 Summary
Chapter 10. Dynamic Routing Protocols
10.1 Intfoduction
10.2 Dynamic Routing
10.3 Unix Routing Daemons
10.4 RIP: Routing Information Protocol
10.5 RIP Version 2
10.6 OSPF:Open Shortest Paih First
10.7 BGP:Border Gateway Protocol
10.8 CIDR:Classless Interdomain Routing
10.9 Summary
Chapter 11. UDP: User Datagram Protocol
11.1 Introduction
11.2 UDP Header
11.3 UDP Checksum
11.4 A Simple Example
11.5 IP Fragmentation
11.6 ICMP Unreachable Error (Fragmentation Required)
11.7 Determining the Path MTU Using Traceroute
11.8 Path MTU Dlscovery with UDP
11.9 Interaction Between UDP and ARP
11.10 Maximum UDP Datagram Size
11.11 ICMP Source Quench Error
11.12 UDP Server Design
11.13 Summary
Chapter 12. Broadcasting and Multicasting
12.1 Introduction
12.2 Broadcasting
12.3 Broadcasting Examples
12.4 Multicasting
12.5 Summary
Chapter 13. IGMP: lnternet Group Management Protocol
13.1 Introduction
13.2 IGMP Message
13.3 IGMP Protocol
13.4 An Example
13.5 Summary
Chapter 14. DNS: The Domain Name System
14.1 Introduction
14.2 DNS Basics
14.3 DNS Message Format
14.4 A Simple Example
14.5 Pointer Queries
14.6 Resource Records
14.7 Caching
14.8 UDP or TCP
14.9 Another Example
14.10 Summary
Chapter 15. TFTP: Trivial File Transfer Protocol
15.1 Introduction
15.2 ProtocoI
15.3 An Examp1e
15.4 Security
15.5 Summary
Chapter 16. BOOTP: Bootstrap Protocol
16.1 Introduction
16.2 BOOTP Packet Format
16.3 An Example
16.4 BOOTP Server Design
16,5 BOOTP Through a Router
16.6 Vendor-Specific Information
16.7 Summary
Chapter 17. TCP: Transmission Control Protocol
17.1 Introduction
17.2 TCP Services
17.3 TCP Header
17.4 Summary
Chapter 18. TCP Connection Establishment and Termination
18.1 Introduction
18.2 Connection Establishment and Termination
18.3 Timeout of Connection Establishment
18.4 Maximum Segment Size
18.5 TCP Half-Close
18.6 TCP State Transition Diagram
18.7 Reset Segments
18.8 Simultaneous Open
18.9 Simultaneous Close
18.10 TCP Options
18.11 TCP Server Desjgn
18.12 Summary
Chapter 19. TCP lnteractive Data Flow
19.1 Introduction
19.2 Interactive Input
19.3 Delayed Acknowledgments
19.4 Nagle Algorithm
19.5 Window Size Advertisements
19.6 Summary
Chapter 20. TCP Bulk Data Flow
20.1 Introduction
20.2 Normal Data Flow
20.3 Sliding Windows
20.4 Window Size
20.5 PUSH Flag
20.6 Slow Start
20.7 Bulk Data Throughput
20.8 Urgent Mode
20.9 Summary
Chapter 21. TCP Timeout and Retransmission
21.1 lntroduction
21.2 Simple Timeout and Retransmission Example
21.3 Round-Trip Time Measurement
21.4 An RTT Example
21.5 Congestion Example
21.6 Congestion AVOldance Algorithm
21.7 Fast Retransmit and Fast Recovery Algorithms
21.8 Congestion Example (Continued)
21.9 Per-Route Metrics
21.10 ICMP Errors
21.11 Repacketization
21.12 Summary
Chapter 22. TCP Persist Timer
22.1 Introduction
22.2 An ExampIe
22.3 Silly Window Syndrome
22.4 Summary
Chapter 23. TCP Keepalive Timer
23.1 Introduction
23.2 Description
23.3 KeepaIive Examples
23.4 Summary
Chapter 24. TCP Futures and Performance
24.1 Introduction
24.2 Path MTU Discovery
24.3 Long Fat Pipes
24.4 Window Scale Option
24.5 Timestamp Option
24.6 PAWS:Protection Against Wrapped Sequence Numbers
24.7 T/TCP: A TCP Extension for Transactions
24.8 TCP Performance
24.9 Summary
Chapter 25. SNMP: Simple Network Management Protocol
25.1 Introduction
25.2 Protocol
25.3 Structure of Management Information
25.4 Object Identjfiers
25.5 Introductfon to the Management Information Base
25.6 Instance Identification
25.7 SimpIe Examples
25.8 Management Information Base (Continued)
25.9 Additional Examples
25.10 Traps
25.11 ASN.1 and BER
25.12 SNMP Version 2
25.13 Summary
Chapter 26. Telnet and Rlogin: Remote Login
26.1 Introduction
26.2 Rlogin Protocol
26.3 Rlogin Examples
26.4 Telnet Protocol
26.5 Telnet Examples
26.6 Summary
Chapter 27. FTP: File Transfer Protocol
27.1 Introduction
27.2 FTP Protocol
27.3 FTP Examples
27.4 Summary
Chapter 28. SMTP: Simple Mail Transfer Protocol
28.1 Introduction
28.2 SMTP Protocol
28.3 SMTP Examples
28.4 SMTP Futures
28.5 Summary
Chapter 29. NFS: Network FiIe System
29.1 Introduction
29.2 Sun Remote Procedure Call
29.3 XDR:External Data Representation
29.4 Port Mapper
29.5 NFS Protocol
29.6 NFS Examples
29.7 NFS Version 3
29.8 Summary
Chapter 30. Other TCP/IP Applications
30.1 Introduction
30.2 Finger Protocol
30.3 Whols Protocol
30.4 Archie, WAIS, Gopher, Veronica, and WWW
30.5 X Window System
30.6 Summary
Appendix A. The tcpdump Program
A.1 BSD Packet Filter
A.2 SunOS Network Interface Tap
A.3 SVR4 Data Link Provider Interface
A.4 tcpdump Output
A.5 Security Considerations
A.6 Socket Debug Option
Appendix B. Computer Clocks
Appendix C. The sock Program
Appendix D. Solutions to Selected Exercises
Appendix E. Configurable Options
E.1 BSD/386 Version 1.0
E.2 SunOS 4.1.3
E.3 System V Release 4
E.4 Solaris 2.2
E.5 AIX 3.2.2
E.6 4.4BSD
Appendix F Source Code Availability
Bibliography
Index