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Top-down network design
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Top-Down Network Design
Third Edition
Priscilla Oppenheimer
Priscilla Oppenheimer
Cisco Press
800 East 96th Street
Indianapolis, IN 46240
Top-Down Network Design, Third Edition
Priscilla Oppenheimer
Copyright© 2011 Cisco Systems, Inc.
Published by:
Cisco Press
800 East 96th Street
Indianapolis, IN 46240 USA
All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means,
electronic or mechanical, including photocopying, recording, or by any information storage and retrieval
system, without written permission from the publisher, except for the inclusion of brief quotations in a
review.
Printed in the United States of America
First Printing August 2010
Library of Congress Cataloging-in-Publication data is on file.
ISBN-13: 978-1-58720-283-4
ISBN-10: 1-58720-283-2
Warning and Disclaimer
This book is designed to provide information about top-down network design. Every effort has been
made to make this book as complete and as accurate as possible, but no warranty or fitness is implied.
The information is provided on an “as is” basis. The author, Cisco Press, and Cisco Systems, Inc. shall have
neither liability nor responsibility to any person or entity with respect to any loss or damages arising from
the information contained in this book or from the use of the discs or programs that may accompany it.
The opinions expressed in this book belong to the author and are not necessarily those of Cisco Systems, Inc.
Trademark Acknowledgments
All terms mentioned in this book that are known to be trademarks or service marks have been appropriately
capitalized. Cisco Press or Cisco Systems, Inc., cannot attest to the accuracy of this information. Use of a
term in this book should not be regarded as affecting the validity of any trademark or service mark.
ii Top-Down Network Design
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iii
Publisher: Paul Boger Manager, Global Certification: Erik Ullanderson
Associate Publisher: Dave Dusthimer Business Operation Manager, Cisco Press: Anand Sundaram
Executive Editor: Mary Beth Ray Technical Editors: Keith Nabozny, Joe Wilson
Managing Editor: Sandra Schroeder Copy Editor: Bill McManus
Senior Development Editor: Christopher Cleveland Book Designer: Louisa Adair
Senior Project Editor: Tonya Simpson Proofreader: Apostrophe Editing Services
Editorial Assistant: Vanessa Evans
Composition: Mark Shirar
Indexer: Tim Wright
About the Author
Priscilla Oppenheimer has been developing data communications and networking systems since 1980 when she earned her master’s degree in information science from the
University of Michigan. After many years as a software developer, she became a technical
instructor and training developer and has taught more than 3000 network engineers from
most of the Fortune 500 companies. Her employment at such companies as Apple
Computer, Network General, and Cisco gave her a chance to troubleshoot real-world network design problems and the opportunity to develop a practical methodology for enterprise network design. Priscilla was one of the developers of the Cisco Internetwork
Design course and the creator of the Designing Cisco Networks course. Priscilla teaches
network design, configuration, and troubleshooting around the world and practices what
she preaches in her network consulting business.
About the Technical Reviewers
Keith Nabozny is a technology consultant with HP, an adjunct professor at Macomb
Community College, and a graduate of Oakland University in Rochester, Michigan. He
has three Cisco professional certifications and is a Certified Information Systems
Security Professional (CISSP). Keith has supported large corporate clients for the past
14 years in operations, implementation, and engineering roles. He is currently supporting
the firewalls of a major manufacturer with locations around the world. Most recently he
taught network design and troubleshooting classes at Macomb Community College.
Keith and his family live in Southeast Michigan.
Joe Wilson, MSCS, PMC, CISSP No. 100304, is a senior network design engineer for
TelcoCapital Systems, LLC. TelcoCapital is a leading provider of Cisco Unified
Communications solutions for small and medium-sized enterprises. Joe is completing his
dissertation toward a PhD in information technology at Capella University (Minneapolis,
MN), with specializations in college teaching and IT security and assurance. Joe has
worked in information technology for the past 20 years and is a retired systems engineer
from The Boeing Company in Seattle, Washington, where he designed airborne NMS
solutions for commercial aircraft. While working for AT&T Broadband Network
Solutions as a broadband systems engineer, Joe designed commercial broadband networks using advanced communications technologies such as ATM, SONET, DWDM, and
Gigabit Ethernet. Joe has been a CISSP since 2006 and has distinguished himself as a
trusted partner in providing secure communications solutions and services to public and
private organizations. Joe teaches courses in the Cisco Networking Academy program at
DeVry University in Federal Way, Washington.
iv Top-Down Network Design
Dedication
To my parents, Dr. Stephen T. Worland, PhD, and Mrs. Roberta Worland, MS. They gave
me an appreciation for knowledge, logic, and analysis, and taught me that “where there’s a
will, there’s a way.”
Acknowledgments
I would like to thank Mary Beth Ray, executive editor at Cisco Press, for giving me the
opportunity to update this book and for marshaling the people and resources needed to
complete the project. I would especially like to thank Christopher Cleveland, Tonya
Simpson, and Bill McManus for their hard work on the book. I am also grateful for the
work of the technical editors, Keith Nabozny and Joe Wilson. In many ways, updating a
book is even harder than writing it in the first place, and I couldn’t have done it without
the help of Chris, Tonya, Bill, Keith, and Joe.
I also wish to thank the technical editors for the first two editions, Matthew Birkner,
Blair Buchanan, Dr. Peter Welcher, Dr. Alex Cannara, David Jansson, and Hank Mauldin.
Their terrific contributions are still evident in the third edition.
I would like to thank other networking professionals who have inspired me over the
years, including Joseph Bardwell and Anita Lenk from Connect802, Laura Chappell and
her terrific Wireshark University, Howard Berkowitz, Paul Borghese, John Neiberger,
Leigh Anne Chisholm, Marty Adkins, Matthias David Moore, Tom Lisa, Scott Vermillion,
and many more.
I am grateful for my colleagues and students in Ashland, Oregon, who have inspired and
entertained me, including Dr. Lynn Ackler, Jeff McJunkin, Andrew Krug, Brandon Kester,
Stephen Perkins, Daniel DeFreeze, Christina Kaiserman, Nicole Colbert, Corey Smith,
Stefan Hutchison, Jesse Williamson, Jonathan McCoy, Jennifer Comstock, Linda
Sturgeon, Kathleen Marrs, Vinnie Moscaritolo, Louis Kowolowski, and Robert Luaders
for his ideas regarding the design scenarios.
I’d like to thank Gary Rubin, Rob Stump, and Kip Peterson from Advanced Network
Information for the many opportunities they’ve given me over the years, in particular the
terrific opportunity to work at Cisco. To my colleagues at Cisco, Patrick Stark, our manager, Lisa Bacani, Walt Sacharok, Dax Mickelson, David Daverso, and Paul Azzi; you are
terrific!
Finally, I would like to thank Alan Oppenheimer, who throughout this project acted as my
technical advisor, therapist, chef, and best friend. I’m glad he doesn’t mind that it was
finally time to remove AppleTalk.
v
Contents at a Glance
Introduction xxii
Part I Identifying Your Customer’s Needs and Goals 1
Chapter 1 Analyzing Business Goals and Constraints 3
Chapter 2 Analyzing Technical Goals and Tradeoffs 25
Chapter 3 Characterizing the Existing Internetwork 59
Chapter 4 Characterizing Network Traffic 87
Part II Logical Network Design 117
Chapter 5 Designing a Network Topology 119
Chapter 6 Designing Models for Addressing and Numbering 167
Chapter 7 Selecting Switching and Routing Protocols 199
Chapter 8 Developing Network Security Strategies 233
Chapter 9 Developing Network Management Strategies 263
Part III Physical Network Design 281
Chapter 10 Selecting Technologies and Devices for Campus Networks 283
Chapter 11 Selecting Technologies and Devices for Enterprise Networks 319
Part IV Testing, Optimizing, and Documenting Your Network
Design 351
Chapter 12 Testing Your Network Design 353
Chapter 13 Optimizing Your Network Design 367
Chapter 14 Documenting Your Network Design 393
Glossary 407
Index 435
vi Top-Down Network Design
Contents
Introduction xxii
Part I Identifying Your Customer’s Needs and Goals 1
Chapter 1 Analyzing Business Goals and Constraints 3
Using a Top-Down Network Design Methodology 3
Using a Structured Network Design Process 5
Systems Development Life Cycles 6
Plan Design Implement Operate Optimize (PDIOO) Network Life Cycle 7
Analyzing Business Goals 8
Working with Your Client 8
Changes in Enterprise Networks 10
Networks Must Make Business Sense 10
Networks Offer a Service 11
The Need to Support Mobile Users 12
The Importance of Network Security and Resiliency 12
Typical Network Design Business Goals 13
Identifying the Scope of a Network Design Project 14
Identifying a Customer’s Network Applications 16
Analyzing Business Constraints 19
Politics and Policies 19
Budgetary and Staffing Constraints 20
Project Scheduling 21
Business Goals Checklist 22
Summary 23
Review Questions 23
Design Scenario 24
Chapter 2 Analyzing Technical Goals and Tradeoffs 25
Scalability 25
Planning for Expansion 26
Expanding Access to Data 26
Constraints on Scalability 27
Availability 27
Disaster Recovery 28
Specifying Availability Requirements 29
vii
Five Nines Availability 30
The Cost of Downtime 31
Mean Time Between Failure and Mean Time to Repair 31
Network Performance 32
Network Performance Definitions 33
Optimum Network Utilization 34
Throughput 35
Throughput of Internetworking Devices 36
Application Layer Throughput 37
Accuracy 38
Efficiency 39
Delay and Delay Variation 40
Causes of Delay 41
Delay Variation 43
Response Time 44
Security 44
Identifying Network Assets 45
Analyzing Security Risks 46
Reconnaissance Attacks 47
Denial-of-Service Attacks 48
Developing Security Requirements 48
Manageability 49
Usability 50
Adaptability 50
Affordability 51
Making Network Design Tradeoffs 52
Technical Goals Checklist 54
Summary 55
Review Questions 56
Design Scenario 56
Chapter 3 Characterizing the Existing Internetwork 59
Characterizing the Network Infrastructure 59
Developing a Network Map 60
Characterizing Large Internetworks 60
Characterizing the Logical Architecture 62
Developing a Modular Block Diagram 64
Characterizing Network Addressing and Naming 64
viii Top-Down Network Design
Characterizing Wiring and Media 65
Checking Architectural and Environmental Constraints 68
Checking a Site for a Wireless Installation 69
Performing a Wireless Site Survey 70
Checking the Health of the Existing Internetwork 71
Developing a Baseline of Network Performance 72
Analyzing Network Availability 73
Analyzing Network Utilization 73
Measuring Bandwidth Utilization by Protocol 75
Analyzing Network Accuracy 76
Analyzing Errors on Switched Ethernet Networks 77
Analyzing Network Efficiency 79
Analyzing Delay and Response Time 80
Checking the Status of Major Routers, Switches, and Firewalls 82
Network Health Checklist 83
Summary 84
Review Questions 84
Hands-On Project 85
Design Scenario 85
Chapter 4 Characterizing Network Traffic 87
Characterizing Traffic Flow 87
Identifying Major Traffic Sources and Stores 87
Documenting Traffic Flow on the Existing Network 89
Characterizing Types of Traffic Flow for New Network Applications 90
Terminal/Host Traffic Flow 91
Client/Server Traffic Flow 91
Peer-to-Peer Traffic Flow 93
Server/Server Traffic Flow 94
Distributed Computing Traffic Flow 94
Traffic Flow in Voice over IP Networks 94
Documenting Traffic Flow for New and Existing Network
Applications 95
Characterizing Traffic Load 96
Calculating Theoretical Traffic Load 97
Documenting Application-Usage Patterns 99
Refining Estimates of Traffic Load Caused by Applications 99
Estimating Traffic Load Caused by Routing Protocols 101
ix
Characterizing Traffic Behavior 101
Broadcast/Multicast Behavior 101
Network Efficiency 102
Frame Size 103
Windowing and Flow Control 103
Error-Recovery Mechanisms 104
Characterizing Quality of Service Requirements 105
ATM QoS Specifications 106
Constant Bit Rate Service Category 107
Real-time Variable Bit Rate Service Category 107
Non-real-time Variable Bit Rate Service Category 107
Unspecified Bit Rate Service Category 108
Available Bit Rate Service Category 108
Guaranteed Frame Rate Service Category 108
IETF Integrated Services Working Group QoS Specifications 109
Controlled-Load Service 110
Guaranteed Service 110
IETF Differentiated Services Working Group QoS Specifications 111
Grade of Service Requirements for Voice Applications 112
Documenting QoS Requirements 113
Network Traffic Checklist 114
Summary 114
Review Questions 114
Design Scenario 115
Summary for Part I 115
Part II Logical Network Design 117
Chapter 5 Designing a Network Topology 119
Hierarchical Network Design 120
Why Use a Hierarchical Network Design Model? 121
Flat Versus Hierarchical Topologies 122
Flat WAN Topologies 122
Flat LAN Topologies 123
Mesh Versus Hierarchical-Mesh Topologies 124
Classic Three-Layer Hierarchical Model 125
Core Layer 127
Distribution Layer 127
x Top-Down Network Design
Access Layer 128
Guidelines for Hierarchical Network Design 128
Redundant Network Design Topologies 130
Backup Paths 131
Load Sharing 132
Modular Network Design 133
Cisco SAFE Security Reference Architecture 133
Designing a Campus Network Design Topology 135
Spanning Tree Protocol 135
Spanning Tree Cost Values 136
Rapid Spanning Tree Protocol 137
RSTP Convergence and Reconvergence 138
Selecting the Root Bridge 139
Scaling the Spanning Tree Protocol 140
Virtual LANs 141
Fundamental VLAN Designs 142
Wireless LANs 144
Positioning an Access Point for Maximum Coverage 145
WLANs and VLANs 146
Redundant Wireless Access Points 146
Redundancy and Load Sharing in Wired LANs 147
Server Redundancy 148
Workstation-to-Router Redundancy 150
Hot Standby Router Protocol 152
Gateway Load Balancing Protocol 153
Designing the Enterprise Edge Topology 153
Redundant WAN Segments 153
Circuit Diversity 154
Multihoming the Internet Connection 154
Virtual Private Networking 157
Site-to-Site VPNs 158
Remote-Access VPNs 159
Service Provider Edge 160
Secure Network Design Topologies 162
Planning for Physical Security 162
Meeting Security Goals with Firewall Topologies 162
xi
Summary 163
Review Questions 165
Design Scenario 165
Chapter 6 Designing Models for Addressing and Numbering 167
Guidelines for Assigning Network Layer Addresses 168
Using a Structured Model for Network Layer Addressing 168
Administering Addresses by a Central Authority 169
Distributing Authority for Addressing 170
Using Dynamic Addressing for End Systems 170
IP Dynamic Addressing 171
IP Version 6 Dynamic Addressing 174
Zero Configuration Networking 175
Using Private Addresses in an IP Environment 175
Caveats with Private Addressing 177
Network Address Translation 177
Using a Hierarchical Model for Assigning Addresses 178
Why Use a Hierarchical Model for Addressing and Routing? 178
Hierarchical Routing 179
Classless Interdomain Routing 179
Classless Routing Versus Classful Routing 180
Route Summarization (Aggregation) 181
Route Summarization Example 182
Route Summarization Tips 183
Discontiguous Subnets 183
Mobile Hosts 184
Variable-Length Subnet Masking 185
Hierarchy in IP Version 6 Addresses 186
Link-Local Addresses 187
Global Unicast Addresses 188
IPv6 Addresses with Embedded IPv4 Addresses 189
Designing a Model for Naming 189
Distributing Authority for Naming 190
Guidelines for Assigning Names 191
Assigning Names in a NetBIOS Environment 192
Assigning Names in an IP Environment 193
The Domain Name System 193
xii Top-Down Network Design
Dynamic DNS Names 194
IPv6 Name Resolution 195
Summary 195
Review Questions 196
Design Scenario 197
Chapter 7 Selecting Switching and Routing Protocols 199
Making Decisions as Part of the Top-Down Network Design Process 200
Selecting Switching Protocols 201
Switching and the OSI Layers 202
Transparent Bridging 202
Selecting Spanning Tree Protocol Enhancements 203
PortFast 204
UplinkFast and BackboneFast 204
Unidirectional Link Detection 205
LoopGuard 206
Protocols for Transporting VLAN Information 207
IEEE 802.1Q 207
Dynamic Trunk Protocol 208
VLAN Trunking Protocol 208
Selecting Routing Protocols 209
Characterizing Routing Protocols 209
Distance-Vector Routing Protocols 210
Link-State Routing Protocols 212
Routing Protocol Metrics 214
Hierarchical Versus Nonhierarchical Routing Protocols 214
Interior Versus Exterior Routing Protocols 214
Classful Versus Classless Routing Protocols 214
Dynamic Versus Static and Default Routing 215
On-Demand Routing 216
Scalability Constraints for Routing Protocols 216
Routing Protocol Convergence 217
IP Routing 218
Routing Information Protocol 218
Enhanced Interior Gateway Routing Protocol 219
Open Shortest Path First 221
Intermediate System-to-Intermediate System 224
Border Gateway Protocol 225
xiii
Using Multiple Routing Protocols in an Internetwork 225
Routing Protocols and the Hierarchical Design Model 226
Redistribution Between Routing Protocols 227
Integrated Routing and Bridging 229
A Summary of Routing Protocols 230
Summary 231
Review Questions 231
Design Scenario 232
Chapter 8 Developing Network Security Strategies 233
Network Security Design 233
Identifying Network Assets 234
Analyzing Security Risks 234
Analyzing Security Requirements and Tradeoffs 235
Developing a Security Plan 235
Developing a Security Policy 236
Components of a Security Policy 237
Developing Security Procedures 237
Maintaining Security 237
Security Mechanisms 238
Physical Security 238
Authentication 239
Authorization 239
Accounting (Auditing) 240
Data Encryption 240
Public/Private Key Encryption 241
Packet Filters 243
Firewalls 244
Intrusion Detection and Prevention Systems 244
Modularizing Security Design 245
Securing Internet Connections 245
Securing Public Servers 246
Securing E-Commerce Servers 247
Securing Remote-Access and VPNs 248
Securing Remote-Access Technologies 248
Securing VPNs 249
Securing Network Services and Network Management 250
Securing Server Farms 251
xiv Top-Down Network Design