Table Of ContentDHCP for Windows 2000
by Neall Alcott
Copyright 2001 O’Reilly & Associates, Inc. All rights reserved.
Printed in the United States of America.
Published by O’Reilly & Associates, Inc, 101 Morris Street, Sebastopol, CA 95472.
Editor: Sue Miller
Production Editor: Leanne Clarke Soylemez
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January 2001: First Edition.
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information contained herein.
Library of Congress Cataloging-in-Publication Data can be found at:
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ISBN: 1-56592-838-5
[M]
Table of Contents
Preface ........................................................... 1
Conventions Used in This Book ....................................... 1
How to Contact Us ................................................. 2
Acknowledgments .................................................. 2
1. TCP/IP Overview ................................................ 4
1.1 The TCP/IP Protocol Suite ........................................ 5
1.2 MAC Addresses ............................................... 11
1.3 IP Addressing ................................................. 14
1.4 DNS and Hostnames ............................................ 21
1.5 WINS and NetBIOS Names ...................................... 24
1.6 Summary .................................................... 28
2. In The Beginning: RARP and BOOTP ............................... 29
2.1 RARP ...................................................... 29
2.2 What Is BOOTP? .............................................. 30
2.3 BOOTP Packet Structure ........................................ 31
2.4 The BOOTP Conversation ....................................... 32
2.5 Summary .................................................... 38
3. Making Life Easier: DHCP ........................................ 39
3.1 Why DHCP? ................................................. 39
3.2 DHCP Packet Structure .......................................... 42
3.3 The DHCP Conversation ......................................... 43
3.4 The DHCP Relay Agent ......................................... 52
3.5 Summary .................................................... 55
4. Designing a DHCP Infrastructure ................................... 56
4.1 Who Needs DHCP? ............................................ 56
4.2 Creating an IP Addressing Plan .................................... 57
4.3 Network Topology ............................................. 64
4.4 DHCP Client Needs ............................................ 65
4.5 Defining Scopes ............................................... 66
4.6 Fault Tolerance ............................................... 67
4.7 Putting It All Together: DHCP Strategies ............................. 68
4.8 Summary .................................................... 73
5. The DHCP Server ............................................... 74
5.1 Introduction to Windows 2000 .................................... 74
5.2 DHCP Server in Windows 2000 ................................... 75
5.3 Installing DHCP Server in Windows 2000 ............................ 76
5.4 The DHCP Console ............................................ 82
5.5 Configuring a DHCP Server ...................................... 85
5.6 Leases ...................................................... 97
5.7 Options ..................................................... 98
5.8 Summary ................................................... 106
6. DHCP Clients ................................................. 108
6.1 Windows 2000 Professional ..................................... 108
6.2 Windows NT Workstation 4.0 .................................... 120
6.3 Windows 9x ................................................. 127
6.4 Windows for Workgroups ....................................... 133
6.5 MS-DOS ................................................... 137
6.6 Summary ................................................... 140
7. Advanced DHCP ............................................... 142
7.1 Superscopes ................................................. 142
7.2 Delegating Administration ...................................... 144
7.3 Using Netsh Commands for DHCP ................................ 145
7.4 Configuring Multihomed DHCP Servers ............................ 150
7.5 The DHCP Database ........................................... 152
7.6 Supporting BOOTP Clients ...................................... 155
7.7 Configuring Cisco Routers ...................................... 155
7.8 Configuring Windows 2000 as a DHCP Relay Agent ................... 157
7.9 Summary ................................................... 159
8. Multicasting: Using MADCAP .................................... 161
8.1 Multicast Address Allocation .................................... 161
8.2 Summary ................................................... 172
9. DHCP Failover: Using Clusters .................................... 173
9.1 Windows Clustering ........................................... 173
9.2 Building a Windows 2000 Cluster ................................. 179
9.3 Summary ................................................... 194
10. Integrating DHCP and DNS ..................................... 195
10.1 Domain Name System ........................................ 195
10.2 Windows 2000 DNS Server ..................................... 195
10.3 Dynamic Update ............................................. 202
10.4 Summary .................................................. 212
11. Monitoring and Troubleshooting DHCP ............................ 213
11.1 Monitoring DHCP ........................................... 213
11.2 Troubleshooting DHCP ........................................ 218
11.3 Summary .................................................. 225
12. What Lies Ahead: IPv6 and DHCPv6 .............................. 226
12.1 IPv6 ...................................................... 226
12.2 DHCP for IPv6 .............................................. 230
12.3 Summary .................................................. 238
A. Appendix:DHCP Options ........................................ 239
Colophon ...................................................... 244
DHCP for Windows 2000
Preface
Dynamic Host Configuration Protocol (DHCP) provides a means of allocating and managing
IP addresses dynamically over a network. Before the advent of DHCP, administrators
configured each host on a network with an IP address, subnet mask, and default gateway.
Maintaining the changes and the logs of the changes took a tremendous amount of time and
was prone to error. DHCP uses a client/server model in which the network information is
maintained and updated dynamically by the system.
This book discusses DHCP in a Windows 2000 environment. It provides an introduction to
the DHCP protocol and shows how to implement a DHCP server into the network. It also
covers the more advanced features of DHCP.
The book begins with an overview of the TCP/IP protocol suite and shows how DHCP
coexists with the rest of the TCP/IP suite. It identifies DHCP's predecessors, RARP and
BOOTP, and explores the reasons that DHCP was developed. DHCP design considerations
are discussed, as well as the different methods of deployment. The book shows how to install
and configure DHCP servers in routed and non-routed environments and how to configure a
client to use DHCP. It also discusses how to administer a DHCP server in Windows 2000
using DHCP scopes, options, and leases. Finally, the book covers DHCP's close relationship
with Dynamic DNS, as well as some of the future directions for DHCP.
Conventions Used in This Book
The following conventions are used throughout this book:
Italic
Used for URLs, filenames, email addresses, and new terms when first defined.
Constant width
Used in examples to show the contents of files or the output from commands.
Constant bold
Used in examples to show commands or other text to be typed by the user.
Constant italic
Used in examples and command syntax definitions to show variables for which a
context-specific substitution should be made.
Indicates a tip, suggestion, or general note.
Indicates a warning.
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DHCP for Windows 2000
How to Contact Us
We have tested and verified the information in this book to the best of our ability, but you
may find that features have changed (or even that we have made mistakes!). Please let us
know about any errors you find, as well as your suggestions for future editions, by writing to:
O'Reilly & Associates, Inc. 101 Morris Street Sebastopol, CA 95472 (800) 998-9938 (in the
U.S. or Canada) (707) 829-0515 (international/local) (707) 829-0104 (fax)
We have a web site for the book, where we list errata, examples, or any additional
information. You can access this page at:
http://www.oreilly.com/catalog/dhcpwin2000
To ask technical questions or comment on the book, send email to:
[email protected]
For more information about our books, conferences, software, Resource Centers, and the
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Acknowledgments
Acknowledgments, acknowledgments, acknowledgments! They are oh so difficult. What if I
forget someone?! Well, let me try my best. If I left anyone out, please take me to lunch so I
can personally thank you . . . your treat of course . . .
This book began to take shape during a phone call with Robert Denn at O'Reilly. We
discussed the curious situation where there were many books for many subjects, but very few
for the oft-used, but little discussed, DHCP. Thus, this book was born. I would also like to
thank Neil Salkind, my agent, and everyone at Studio B for all of their help.
At O'Reilly, I would like to thank Sue Miller, my editor. Sue was instrumental in keeping this
project moving forward and sharpening my work. I especially need to thank Leanne Soylemez
for her thoroughness as the production editor and Rob Romano for redrawing my crappy . . .
err . . . displeasing figures.
And of course, the tech reviewers honed the details and, in the end, created a better book. I
must thank Andre Paree-Huff, Rory Winston, and Jim Boyce.
I must say I was very fortunate to work with the finest IT team around: System Support at
AstraZeneca Chesterbrook. Many thanks and memories go to Bill "The Fridge" Friedgen,
Chuck "Chooch" Boohar, Frank "No, not Kathy Lee's hubby, the decent one" Gifford, Mark
"When I was a . . . " Clayton, Richard "This is Richard!" Muir, Mike "Polly" Kliwinski, Matt
"Good eats" McWilliams, Tina Hughes, Tina Mohler, Adara Santillo (J), Paul "Hoagie Man"
Kern, Sandy "Could you please come to the data center" Garlinski, Ed "Salt Shaker"
Cartright, Steve Urick, The Honorable Marvin Mayes, George "The Agent" Oschenreither,
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DHCP for Windows 2000
Chris Pignone, Ed Murawski, David Short, Rich Donato, and finally, the Men in Black: Brian
"Morphius" Seltzer and Jeff "The Angry Man" Sisson. Tell the Culinary Engineer at the
Deltaga I said hello and the coffee is weak.
Nor shall I ever forget the Ghosts of System Support's Past (kill the lights and queue the sad
music):
Jeff Tincher and Mark Marshall, both currently haunting Brandycare.
Jim Lange, rattling chains at Merck.
Bill Juliana, the only spirit wearing boat shoes and changing CDs at Comverse.
Lise Leonard, casually floating through the halls of Yoh.
And most of all I must thank my wife, Ginny, and my daughters, Lauren and Lindsey. Thank
you for always making me laugh and letting me know that play must always be more
important than work. The breaks that I took with you made it possible to recharge my
batteries and forge ahead with this project. I am forever grateful for your love and support.
—Neall Alcott
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DHCP for Windows 2000
Chapter 1. TCP/IP Overview
Dynamic Host Configuration Protocol (DHCP) is an Internet standard protocol designed to
dynamically allocate and distribute IP addresses as well as additional TCP/IP configuration
information. DHCP is defined by RFCs 2131 and 2132. Working with the Internet
Engineering Task Force (IETF) and a number of other vendors, Microsoft was instrumental in
the development and standardization of DHCP.
Before the advent of DHCP, most TCP/IP configurations were maintained statically. An
administrator configured each individual host with a valid IP address, subnet mask, and
default gateway, as well as other TCP/IP configuration parameters. As you can guess,
configuring and administrating static TCP/IP configurations for multiple workstations and
network devices can be a burdensome task, especially if the network is large and/or changes
frequently. The exception to the rule was the use of two predecessors to DHCP, the RARP
and BOOTP protocols. These protocols are covered in more detail in Chapter 2.
DHCP uses a client/server model of operation (see Figure 1.1), where a DHCP client makes a
request to a DHCP server for an IP address and other configuration parameters. When the
DHCP client makes the request, the DHCP server assigns it an IP address and updates its
database, noting which client has the address and the amount of time that the address can be
used. This amount of time is known as a lease. When the time expires, the DHCP client needs
to renew the lease or negotiate a new lease for a different IP address. Through the use of
leases, the DHCP server can reclaim unused IP addresses.
Figure 1.1. The DHCP client/server model
Using DHCP allows an administrator to make changes to a client's IP configuration without
the need to visit each and every client. The user at the workstation only needs to release and
renew their DHCP lease. That is the power and benefit of DHCP.
The purpose of this chapter is to provide an overview of the data that DHCP is expected to
deliver: TCP/IP configuration information. The TCP/IP protocol suite is the common
language of the Internet and by far the dominant networking protocol suite in use today. One
must understand the many different facets of the TCP/IP protocol suite in order to configure,
maintain, and troubleshoot a Windows 2000 DHCP server.
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DHCP for Windows 2000
This chapter begins with an overview of the TCP/IP protocol suite, describing the different
functions at the different layers of the Open Systems Interconnection (OSI) Model. It then
covers Media Access Control (MAC) addresses—what they are and how they operate,
followed by a very important area that one must understand: IP addressing and subnetting.
The next two sections finish up the chapter by giving an overview of the two types of name
resolution used in Microsoft Networking: DNS and WINS.
1.1 The TCP/IP Protocol Suite
In the 1960s, the Department of Defense's Defense Advanced Research Projects Agency
(DARPA) was in charge of developing a means of communication that would still function in
the event of a nuclear war. Development focused on the new theory of the packet-switched
network. All forms of networking up to this time (i.e., the phone system) had used a circuit-
switched network.
A circuit-switched network connects the sending and receiving stations by a single, direct
physical path. Circuit-switched connections are not shared with other traffic; they are meant
to be one-to-one. The telephone system is an example of a circuit-switched network. When a
person dials a phone number, the phone company equipment establishes a direct connection
between the caller's phone and the receiving phone. This connection lasts for the duration of
the call.
A packet-switched network operates by breaking the data to be transmitted into smaller
datagrams or packets. Each of these packets is numbered and sent out across the network.
Because the packets are individually numbered, they can take multiple paths to their
destination. There they will be put back in order and reassembled into the original data.
Figure 1.2 illustrates the concepts of these two types of networks.
Figure 1.2. Circuit-switched and packet-switched networks
The weakness with a circuit-switched network is that communication links have to be set up
ahead of time. If a circuit goes down, communication stops. The beauty of a packet-switched
network is that if a point of communication goes down, the data is automatically rerouted
through another location dynamically. In the end, it had great battlefield potential—which is
what DARPA was looking for. If a command center was taken out, communications could
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DHCP for Windows 2000
continue by rerouting the data across any available medium: packet radio, satellite links, land
links, etc.
The TCP/IP protocol suite was developed and refined as part of the packet-switched network
project.
1.1.1 The OSI and DOD Reference Models
The TCP/IP protocol suite can be used to communicate over any type of networking medium.
This includes Local Area Network (LAN) and Wide Area Network (WAN) environments.
TCP/IP accomplishes this by using a modular design. The blueprint of this modular design
comes from the Department of Defense (DOD) Reference Model. The International Standard
Organization (ISO) also developed a seven-layer reference model called the Open Systems
Interconnection (OSI) Model. These models provide networking hardware and software
vendors with guidelines to create products that will be compatible in form and function across
multiple hardware and operating system platforms.
The DOD Reference Model consists of only four layers that are closely aligned with the OSI
Reference Model (see Figure 1.3):
Application Layer
This layer provides application interfaces, session establishment, data formatting, and
data conversion for applications running on a host system. This layer coincides with
the upper three layers of the OSI Model: Application Layer, Presentation Layer, and
Session Layer.
Transport Layer
This layer defines the method of communication between two systems: connection-
oriented or connectionless. This layer maps directly to the Transport Layer in the OSI
Model.
Internet Layer
The Internet Layer defines internetworking communications (i.e., routing). This layer
maps directly to the Network Layer of the OSI Model.
Network Interface Layer
This layer defines data-link and media access methods (i.e., Ethernet, Token Ring,
FDDI). This layer includes the remaining two layers of the OSI Model: Data Link and
Physical Layers.
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