Internet Core Protocols: The Definitive Guide: Help for Network Administrators

474 Pages·2000·3.66 MB·English

by  Eric Hall

Internet Core Protocols
The Definitive Guide

Internet Core Protocols
The Definitive Guide
Eric A. Hall
Beijing• Cambridge• Farnham• Köln• Paris• Sebastopol• Taipei• Tokyo
Internet Core Protocols: The Definitive Guide
by Eric A. Hall
Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved.
Printed in the United States of America.
Published by O’Reilly & Associates, Inc., 1005 Gravenstein Highway North, Sebastopol, CA
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Editor:Mike Loukides
Production Editor:Nicole Arigo
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Printing History:
February 2000: First Edition.
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Library of Congress Cataloging-in-Publication Data:
Hall, Eric A.
Internet core protocols : the definitive guide / Eric A. Hall.
p. cm.
Includes bibliographical references.
ISBN 1-56592-572-6 (alk. paper)
1. Internet (Computer network) 2. Computer network protocols. I. Title.
TK5105.875.I57 H355 2000
004.6'2--dc21
99-089559
ISBN: 1-56592-572-6 [02/04]
[M]
Table of Contents
Foreword ............................................................................................................... vii
Preface ..................................................................................................................... xi
1. An Introduction to TCP/IP ..................................................................... 1
A Brief History of the Internet ......................................................................... 1
TCP/IP’s Architecture ....................................................................................... 6
TCP/IP Protocols and Services In-Depth ...................................................... 11
How Application Protocols Communicate Over IP ..................................... 26
2. The Internet Protocol ............................................................................ 31
The IP Standard .............................................................................................. 32
The IP Header ................................................................................................ 56
IP in Action ..................................................................................................... 86
Troubleshooting IP ........................................................................................ 94
3. The Address Resolution Protocol ...................................................... 97
The ARP Standard .......................................................................................... 98
The ARP Packet ............................................................................................ 113
ARP in Action ............................................................................................... 126
Debugging ARP Problems ........................................................................... 132
4. Multicasting and the Internet Group Management
Protocol .....................................................................................................135
The IP Multicasting and IGMP Specifications ............................................. 137
IGMP Messages ............................................................................................ 150
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vi Table of Contents
Multicasting and IGMP in Action ................................................................ 165
Troubleshooting Multicasts and IGMP ........................................................ 168
5. The Internet Control Message Protocol ........................................ 172
The ICMP Specification ................................................................................ 173
ICMP Messages ............................................................................................. 195
ICMP in Action ............................................................................................. 229
Troubleshooting ICMP ................................................................................. 245
6. The User Datagram Protocol ........................................................... 250
The UDP Standard ....................................................................................... 251
The UDP Header .......................................................................................... 258
Troubleshooting UDP .................................................................................. 263
7. The Transmission Control Protocol ............................................... 268
The TCP Standard ........................................................................................ 269
The TCP Header ........................................................................................... 327
TCP in Action ............................................................................................... 360
Troubleshooting TCP ................................................................................... 384
A. The Internet Standardization Process .......................................... 399
B. IP Addressing Fundamentals ........................................................... 407
C. Using the CD-ROM ................................................................................ 417
Bibliography ..................................................................................................... 425
Index .................................................................................................................... 429
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Foreword
The Internet began as a research effort to link different kinds of packet-switched
networks in such a way that the computers that were attached to each of the
packet networks did not need to know anything about the nature of or the exist-
ence of any networks other than the ones to which the host was directly con-
nected. What emerged was a layered design that used encapsulation to carry end-
to-end “Internet” packets from the source host, through intermediate networks and
gateways to the destination host. The first Internet incorporated three wide/
medium area networks including the ARPAnet, the Atlantic Packet Satellite net
(SATNET), and a ground mobile Packet Radio network (PRNET). Eventually it also
included the first 3 MB/s Ethernet developed at Xerox PARC in 1973.
Now, some twenty-five years after the first designs, there are hundreds of thou-
sands of networks comprising the Internet, serving an estimated 45 million com-
puters and 150 million users. Moreover, the original speeds of the trunking circuits
in the constituent networks have increased from thousands of bits per second to
billions of bits per second, with trillions of bits per second lurking in laboratory
demonstrations. As the Internet has grown, its complexity and the number of peo-
ple dependent on it have both increased substantially. But the number of people
with detailed understanding of the protocols and systems that allow the Internet to
work represent a declining fraction of the total population of users or even opera-
tors of such networks.
Worse still is the fact that the number of protocols and services in use on those
networks has also increased from a handful to hundreds. While it used to be that a
single super-administrator could manage the routers, domain name servers, mail
servers, and other resources on the network, we are now faced with so much spe-
cialization that it seems impossible for any one person to follow everything. At
many of the larger firms, there are entire departments that do nothing but manage
vii
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viii Foreword
the network routers, while other groups manage the dial-up servers and still oth-
ers manage the web and mail systems, domain name systems, and newsgroups.
This is a serious problem. Large corporations can afford to hire specialists who
understand their respective parts of the overall picture, but most companies can’t
afford an army of specialists, and have to make do with a handful of network
engineers who have to know “whatever’s necessary.” Furthermore, debugging and
analyzing Internet problems defies specialization. Problems often arise because of
the interactions between different parts of the network. If email isn’t being deliv-
ered, is the problem with the mail server itself? Or has something gone wrong with
routing, the domain name system, or with the low-level protocols that map Ether-
net addresses to Internet addresses? It may be unrealistic to expect one person to
diagnose problems in all of these areas (plus a dozen more), but many network
operators face this challenge daily.
When problems do occur, administrators have a variety of tools available for
debugging purposes. This includes packet analyzers that can show you the inner
core of the network traffic, although they won’t tell you what that traffic means.
Another set of tools is the vendor’s own documentation, although more often than
not the vendor’s documentation is based on the same misreading of the specs as
the problematic software. One of the last alternatives is for the administrator to
prowl through the protocol’s technical specifications in order to determine where
the problem really lies. But when it’s 4 a.m. and the web server in Chicago keeps
dropping its connection to the database server in Atlanta, these specifications are
of limited use. These documents were written largely as strict definitions of behav-
ior that should occur, and generally do not describe ways in which the protocols
might be made to fail.
That’s why these books were written. Throughout this series, Eric Hall takes you
behind the scenes to discover the function and rationale behind the protocols used
on IP networks, offering thorough examinations of the theory behind how things
are supposed to work. Furthermore, Hall backs up the tutorial-oriented discussion
with packet captures from real-world monitoring tools, providing an indispens-
able reference for when you need to know what a particular field in a specific
packet is supposed to look like. In addition, Hall also discusses the common
symptoms of what things look like when they break, providing detailed clues and
discussions on the most common interoperability problems.
This three-way combination of tutorial/reference/debugging-guide essentially
makes these books all-inclusive “owner’s manuals” for IP-based networks. They
are attractive volumes for any network manager who works with Internet technol-
ogies, particularly as the Internet continues to go through the growing pains result-
ing from near-exponential growth. Even though there are already more than 44
million devices connected now, all indications point to there being nearly a billion
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