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TCP/IP Illustrated, Volume 2: The Implementation

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TCP/IP Illustrated, Volume 2: The Implementation


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  • Copyright 1995
  • Dimensions: 7-3/8" x 9-1/4"
  • Edition: 1st
  • Book
  • ISBN-10: 0-201-63354-X
  • ISBN-13: 978-0-201-63354-2

TCP/IP Illustrated, an ongoing series covering the many facets of TCP/IP, brings a highly-effective visual approach to learning about this networking protocol suite.

TCP/IP Illustrated, Volume 2 contains a thorough explanation of how TCP/IP protocols are implemented. There isn't a more practical or up-to-date bookothis volume is the only one to cover the de facto standard implementation from the 4.4BSD-Lite release, the foundation for TCP/IP implementations run daily on hundreds of thousands of systems worldwide.

Combining 500 illustrations with 15,000 lines of real, working code, TCP/IP Illustrated, Volume 2 uses a teach-by-example approach to help you master TCP/IP implementation. You will learn about such topics as the relationship between the sockets API and the protocol suite, and the differences between a host implementation and a router. In addition, the book covers the newest features of the 4.4BSD-Lite release, including multicasting, long fat pipe support, window scale, timestamp options, and protection against wrapped sequence numbers, and many other topics.

Comprehensive in scope, based on a working standard, and thoroughly illustrated, this book is an indispensable resource for anyone working with TCP/IP.


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TCP/IP: The Interface Layer

Table of Contents

(All chapters conclude with a Summary.)

1. Introduction.


Source Code Presentation.


Application Programming Interfaces.

Example Program.

System Calls and Library Functions.

Network Implementation Overview.


Mbufs (Memory Buffers) and Output Processing.

Input Processing.

Network Implementation Overview Revisited.

Interrupt Levels and Concurrency.

Source Code Organization.

Test Network.

2. Mbufs.

Memory Buffers: Introduction.

Code Introduction.

Mbuf Definitions.

mbuf Structure.

Simple Mbuf Macros and Functions.

m_devget and m_pullup Functions.

Summary of Mbuf Macros and Functions.

Summary of Net/3 Networking Data Structures.

m_copy and Cluster Reference Counts.


3. Interface Layer.


Code Introduction.

ifnet Structure.

ifaddr Structure.

sockaddr Structure.

ifnet and ifaddr Specialization.

Network Initialization Overview.

Ethernet Initialization.

SLIP Initialization.

Loopback Initialization.

if_attach Function.

ifinit Function.

4. Interfaces.

Ethernet: Introduction.

Code Introduction.

Ethernet Interface.

ioctl System Call.

5. Interfaces.

SLIP and Loopback: Introduction.

Code Introduction.

SLIP Interface.

Loopback Interface.

6. IP Addressing.


Code Introduction.

Interface and Address Summary.

sockaddr_in Structure.

in_ifaddr Structure.

Address Assignment.

Interface ioctl Processing.

Internet Utility Functions.

ifnet Utility Functions.

7. Domains and Protocols.


Code Introduction.

domain Structure.

protosw Structure.

IP domain and protosw Structures.

pffindproto and pffindtype Functions.

pfctlinput Function.

IP Initialization.

sysctl System Call.

8. IP: Internet Protocol.


Code Introduction.

IP Packets.

Input Processing: ipintr Function.

Forwarding: ip_forward Function.

Output Processing: ip_output Function.

Internet Checksum: in_cksum Function.

setsockopt and getsockopt System Calls.

ip_sysctl Function.

9. IP Option Processing.


Option Format.

ip_dooptions Function.

Record Route Option.

Source and Record Route Options.

Timestamp Option.

ip_insertoptions Function.

ip_pcbopts Function.


10. IP Fragmentation and Reassembly.


Code Introduction.


ip_optcopy Function.


ip_reass Function.

ip_slowtimo Function.

11. ICMP: Internet Control Message Protocol.


Code Introduction.

icmp Structure.

ICMP protosw Structure.

Input Processing: icmp_input Function.

Error Processing.

Request Processing.

Redirect Processing.

Reply Processing.

Output Processing.

icmp_error Function.

icmp_reflect Function.

icmp_send Function.

icmp_sysctl Function.

12. IP Multicasting.


Code Introduction.

Ethernet Multicast Addresses.

ether_multi Structure.

Ethernet Multicast Reception.

in_multi Structure.

ip_moptions Structure.

Multicast Socket Options.

Multicast TTL Values.

ip_setmoptions Function.

Joining an IP Multicast Group.

Leaving an IP Multicast Group.

ip_getmoptions Function.

Multicast Input Processing: ipintr Function.

Multicast Output Processing: ip_output Function.

Performance Considerations.

13. IGMP: Internet Group Management Protocol.


Code Introduction.

igmp Structure.

IGMP protosw Structure.

Joining a Group: igmp_joingroup Function.

igmp_fasttimo Function.

Input Processing: igmp_input Function.

Leaving a Group: igmp_leavegroup Function.

14. IP Multicast Routing.


Code Introduction.

Multicast Output Processing Revisited.

ip_mrouted Daemon.

Virtual Interfaces.

IGMP Revisited.

Multicast Routing.

Multicast Forwarding: ip_mforward Function.

Cleanup: ip_mrouter_done Function.

15. Socket Layer.


Code Introduction.

socket Structure.

System Calls.

Processes, Descriptors, and Sockets.

socket System Call.

getsock and sockargs Functions.

bind System Call.

listen System Call.

tsleep and wakeup Functions.

accept System Call.

sonewconn and soisconnected Functions.

connect System call.

shutdown System Call.

close System Call.

16. Socket I/O.


Code Introduction.

Socket Buffers.

write, writev, sendto, and sendmsg System Calls.

sendmsg System Call.

sendit Function.

sosend Function.

read, readv, recvfrom, and recvmsg System Calls.

recvmsg System Call.

recvit Function.

soreceive Function.

soreceive Code.

select System Call.

17. Socket Options.


Code Introduction.

setsockopt System Call.

getsockopt System Call.

fcntl and ioctl System Calls.

getsockname System Call.

getpeername System Call.

18. Radix Tree Routing Tables.


Routing Table Structure.

Routing Sockets.

Code Introduction.

Radix Node Data Structures.

Routing Structures.

Initialization: route_init and rtable_init Functions.

Initialization: rn_init and rn_inithead Functions.

Duplicate Keys and Mask Lists.

rn_match Function.

rn_search Function.

19. Routing Requests and Routing Messages.


rtalloc and rtalloc1 Functions.

RTFREE Macro and rtfree Function.

rtrequest Function.

rt_setgate Function.

rtinit Function.

rtredirect Function.

Routing Message Structures.

rt_missmsg Function.

rt_ifmsg Function.

rt_newaddrmsg Function.

rt_msg1 Function.

rt_msg2 Function.

sysctl_rtable Function.

sysctl_dumpentry Function.

sysctl_iflist Function.

20. Routing Sockets


routedomain and protosw Structures.

Routing Control Blocks.

raw_init Function.

route_output Function.

rt_xaddrs Function.

rt_setmetrics Function.

raw_input Function.

route_usrreq Function.

raw_usrreq Function.

raw_attach, raw_detach, and raw_disconnect Functions.

21. ARP: Address Resolution Protocol.


ARP and the Routing Table.

Code Introduction.

ARP Structures.

arpwhohas Function.

arprequest Function.

arpintr Function.

in_arpinput Function.

ARP Timer Functions.

arpresolve Function.

arplookup Function.

Proxy ARP.

arp_rtrequest Function.

ARP and Multicasting.

22. Protocol Control Blocks.


Code Introduction.

inpcb Structure.

in_pcballoc and in_pcbdetach Functions.

Binding, Connecting, and Demultiplexing.

in_pcblookup Function.

in_pcbbind Function.

in_pcbconnect Function.

in_pcbdisconnect Function.

in_setsockaddr and in_setpeeraddr Functions.

in_pcbnotify, in_rtchange, and in_losing Functions.

Implementation Refinements.

23. UDP: User Datagram Protocol.


Code Introduction.

UDP protosw Structure.

UDP Header.

udp_init Function.

udp_output Function.

udp_input Function.

udp_saveopt Function.

udp_ctlinput Function.

udp_usrreq Function.

udp_sysctl Function.

Implementation Refinements.

24. TCP: Transmission Control Protocol.


Code Introduction.

TCP protosw Structure.

TCP Header.

TCP Control Block.

TCP State Transition Diagram.

TCP Sequence Numbers.

tcp_init Function.

25. TCP Timers.


Code Introduction.

tcp_canceltimers Function.

tcp_fasttimo Function.

tcp_slowtimo Function.

tcp_timers Function.

Retransmission Timer Calculations.

tcp_newtcpcb Function.

tcp_setpersist Function.

tcp_xmit_timer Function.

Retransmission Timeout: tcp_timers Function.

An RTT Example.

26. TCP Output.


tcp_output Overview.

Determine if a Segment Should be Sent.

TCP Options.

Window Scale Option.

Timestamp Option.

Send a Segment.

tcp_template Function.

tcp_respond Function.

27. TCP Functions.


tcp_drain Function.

tcp_drop Function.

tcp_close Function.

tcp_mss Function.

tcp_ctlinput Function.

tcp_notify Function.

tcp_quench Function.

TCP_REASS Macro and tcp_reass Function.

tcp_trace Function.

28. TCP Input.


Preliminary Processing.

tcp_dooptions Function.

Header Prediction.

TCP Input: Slow Path Processing.

Completion of Passive Open or Active Open.

PAWS: Protection Against Wrapped Sequence Numbers.

Trim Segment so Data is Within Window.

Self-Connects and Simultaneous Opens.

Record Timestamp.

RST Processing.

29. TCP Input (Continued).


ACK Processing Overview.

Completion of Passive Opens and Simultaneous Opens.

Fast Retransmit and Fast Recovery Algorithms.

ACK Processing.

Update Window Information.

Urgent Mode Processing.

tcp_pulloutofband Function.

Processing of Received Data.

FIN Processing.

Final Processing.

Implementation Refinements.

Header Compression.

30. TCP User Requests.


tcp_usrreq Function.

tcp_attach Function.

tcp_disconnect Function.

tcp_usrclosed Function.

tcp_ctloutput Function.

31. BPF: BSD Packet Filter.


Code Introduction.

bpf_if Structure.

bpf_d Structure.

BPF Input.

BPF Output.

32. Raw IP.


Code Introduction.

Raw IP protosw Structure.

rip_init Function.

rip_input Function.

rip_output Function.

rip_usrreq Function.

rip_ctloutput Function.


Appendix A. Solutions to Selected Exercises.

Appendix B. Source Code Availability.

Appendix C. RFC 1122 Compliance.

Link-Layer Requirements.

IP Requirements.

IP Options Requirements.

IP Fragmentation and Reassembly Requirements.

ICMP Requirements.

Multicasting Requirements.

IGMP Requirements.

Routing Requirements.

ARP Requirements.

UDP Requirements.

TCP Requirements.


Index. 020163354XT04062001



This book describes and presents the source code for the common reference implementation of TCP/IP: the implementation from the Computer Systems Research Group (CSRG) at the University of California at Berkeley. Historically this has been distributed with the 4.x BSD system (Berkeley Software Distribution). This implementation was first released in 1982 and has survived many significant changes, much fine tuning, and numerous ports to other Unix and non-Unix systems. This is not a toy implementation, but the foundation for TCP/IP implementations that are run daily on hundreds of thousands of systems worldwide. This implementation also provides router functionality, letting us show the differences between a host implementation of TCP/IP and a router.

We describe the implementation and present the entire source code for the kernel implementation of TCP/IP, approximately 15,000 lines of C code. The version of the Berkeley code described in this text is the 4.4BSD-Lite release. This code was made publicly available in April 1994, and it contains numerous networking enhancements that were added to the 4.3BSD Tahoe release in 1988, the 4.3BSD Reno release in 1990, and the 4.4BSD release in 1993. (App sourceB describes how to obtain this source code.) The 4.4BSD release provides the latest TCP/IP features, such as multicasting and long fat pipe support (for high-bandwidth, long-delay paths). {Fig 1.1} (p. 4) provides additional details of the various releases of the Berkeley networking code.

This book is intended for anyone wishing to understand how the TCP/IP protocols are implemented: programmers writing network applications, system administrators responsible for maintaining computer systems and networks utilizing TCP/IP, and any programmer interested in understanding how a large body of nontrivial code fits into a real operating system.

Organization of the Book

We take a bottom-up approach to the TCP/IP protocol suite, starting at the data-link layer, then the network layer (IP, ICMP, IGMP, IP routing, and multicast routing), followed by the socket layer, and finishing with the transport layer (UDP, TCP, and raw IP).

Intended Audience

This book assumes a basic understanding of how the TCP/IP protocols work. Readers unfamiliar with TCP/IP should consult the first volume in this series, Stevens 1994, for a thorough description of the TCP/IP protocol suite. This earlier volume is referred to throughout the current text as Volume 1. The current text also assumes a basic understanding of operating system principles.

We describe the implementation of the protocols using a data-structures approach. That is, in addition to the source code presentation, each chapter contains pictures and descriptions of the data structures used and maintained by the source code. We show how these data structures fit into the other data structures used by TCP/IP and the kernel. Heavy use is made of diagrams throughout the text - there are over 250 diagrams. This data-structures approach allows readers to use the book in various ways. Those interested in all the implementation details can read the entire text from start to finish, following through all the source code. Others might want to understand how the protocols are implemented by understanding all the data structurestand reading all the text, but not following through all the source code.

We anticipate that many readers are interested in specific portions of the book and will want to go directly to those chapters. Therefore many forward and backward references are provided throughout the text, along with a thorough index, to allow individual chapters to be studied by themselves. The inside back covers contain an alphabetical cross-reference of all the functions and macros described in the book and the starting page number of the description. Exercises are provided at the end of the chapters; most solutions are in Appendix A to maximize the usefulness of the text as a self-study reference.

Source Code Copyright

All of the source code presented in this book, other than Figures 1.2 and 8.27, is from the 4.4BSD-Lite distribution. This software is publicly available through many sources (Appendix B). All of this source code contains the following copyright notice:



We thank the technical reviewers who read the manuscript and provided important feedback on a tight timetable: Ragnvald Blindheim, Jon Crowcroft, Sally Floyd, Glen Glater, John Gulbenkian, Don Hering, Mukesh Kacker, Berry Kercheval, Brian W. Kernighan, Ulf Kieber, Mark Laubach, Steven McCanne, Craig Partridge, Vern Paxson, Steve Rago, Chakravardhi Ravi, Peter Salus, Doug Schmidt, Keith Sklower, Ian Lance Taylor, and G. N. Ananda Vardhana. A special thanks to the consulting editor, Brian Kernighan, for his rapid, thorough, and helpful reviews throughout the course of the project, and for his continued encouragement and support.

Our thanks (again) to the National Optical Astronomy Observatories (NOAO), especially Sidney Wolff, Richard Wolff, and Steve Grandi, for providing access to their networks and hosts. Our thanks also to the U.C. Berkeley CSRG: Keith Bostic and Kirk McKusick provided access to the latest 4.4BSD system, and Keith Sklower provided the modifications to the 4.4BSD-Lite software to run under BSD/386 V1.1.

G.R.W. wishes to thank John Wait, for several years of gentle prodding; Dave Schaller, for his encouragement; and Jim Hogue, for his support during the writing and production of this book.

W.R.S. thanks his family, once again, for enduring another "small" book project. Thank you Sally, Bill, Ellen, and David.

The hardwork, professionalism, and support of the team at Addison-Wesley has made the authors' job that much easier. In particular, we wish to thank John Wait for his guidance and Kim Dawley for her creative ideas.

Camera-ready copy of the book was produced by the authors. It is only fitting that a book describing an industrial-strength software system be produced with an industrial-strength text processing system. Therefore one of the authors chose to use the Groff package written by James Clark, and the other author agreed begrudgingly.

We welcome electronic mail from any readers with comments, suggestions, or bug fixes: tcpipiv2-book@aw.com. Each author will gladly blame the other for any remaining errors.

Gary R. Wright
Middletown, Connecticut

W. Richard Stevens
Tucson, Arizona

November 1994




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