Published by Cisco Press (August 24, 2010) © 2011
Priscilla OppenheimerProduct Information
Objectives
The purpose of Top-Down Network Design, Third Edition, is to help you design networks that meet a customer’s business and technical goals. Whether your customer is another department within your own company or an external client, this book provides you with tested processes and tools to help you understand traffic flow, protocol behavior, and internetworking technologies. After completing this book, you will be equipped to design enterprise networks that meet a customer’s requirements for functionality, capacity, performance, availability, scalability, affordability, security, and manageability.
Audience
This book is for you if you are an internetworking professional responsible for designing and maintaining medium- to large-sized enterprise networks. If you are a network engineer, architect, or technician who has a working knowledge of network protocols and technologies, this book will provide you with practical advice on applying your knowledge to internetwork design.
This book also includes useful information for consultants, systems engineers, and sales engineers who design corporate networks for clients. In the fast-paced presales environment of many systems engineers, it often is difficult to slow down and insist on a top-down, structured systems analysis approach. Wherever possible, this book includes shortcuts and assumptions that can be made to speed up the network design process.
Finally, this book is useful for undergraduate and graduate students in computer science and information technology disciplines. Students who have taken one or two courses in networking theory will find Top-Down Network Design, Third Edition, an approachable introduction to the engineering and business issues related to developing real-world networks that solve typical business problems.
Changes for the Third Edition
Networks have changed in many ways since the second edition was published. Many legacy technologies have disappeared and are no longer covered in the book. In addition, modern networks have become multifaceted, providing support for numerous bandwidth-hungry applications and a variety of devices, ranging from smart phones to tablet PCs to high-end servers. Modern users expect the network to be available all the time, from any device, and to let them securely collaborate with coworkers, friends, and family. Networks today support voice, video, high-definition TV, desktop sharing, virtual meetings, online training, virtual reality, and applications that we can’t even imagine that brilliant college students are busily creating in their dorm rooms.
As applications rapidly change and put more demand on networks, the need to teach a systematic approach to network design is even more important than ever. With that need in mind, the third edition has been retooled to make it an ideal textbook for college students. The third edition features review questions and design scenarios at the end of each chapter to help students learn top-down network design.
To address new demands on modern networks, the third edition of Top-Down Network Design also has updated material on the following topics:
¿ Network redundancy
¿ Modularity in network designs
¿ The Cisco SAFE security reference architecture
¿ The Rapid Spanning Tree Protocol (RSTP)
¿ Internet Protocol version 6 (IPv6)
¿ Ethernet scalability options, including 10-Gbps Ethernet and Metro Ethernet
¿ Network design and management tools
Introduction
Part I Identifying Your Customer’s Needs and Goals
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
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
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
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
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
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
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
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
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
Securing User Services 252
Securing Wireless Networks 253
Authentication in Wireless Networks 254
Data Privacy in Wireless Networks 258
Summary 261
Review Questions 261
Design Scenario 262
Chapter 9 Developing Network Management Strategies 263
Network Management Design 263
Proactive Network Management 264
Network Management Processes 264
Fault Management 265
Configuration Management 266
Accounting Management 266
Performance Management 266
Security Management 268
Network Management Architectures 269
In-Band Versus Out-of-Band Monitoring 270
Centralized Versus Distributed Monitoring 270
Selecting Network Management Tools and Protocols 271
Selecting Tools for Network Management 271
Simple Network Management Protocol 271
Management Information Bases (MIB) 272
Remote Monitoring (RMON) 273
Cisco Discovery Protocol 274
Cisco NetFlow Accounting 276
Estimating Network Traffic Caused by Network Management 276
Summary 277
Review Questions 278
Design Scenario 278
Summary for Part II 279
Part III Physical Network Design
Chapter 10 Selecting Technologies and Devices for Campus Networks 283
LAN Cabling Plant Design 284
Cabling Topologies 284
Building-Cabling Topologies 285
Campus-Cabling Topologies 285
Types of Cables 285
LAN Technologies 289
Ethernet Basics 290
Ethernet and IEEE 802.3 290
Ethernet Technology Choices 291
Half-Duplex and Full-Duplex Ethernet 292
100-Mbps Ethernet 292
Gigabit Ethernet 293
10-Gbps Ethernet 295
Selecting Internetworking Devices for a Campus Network Design 299
Criteria for Selecting Campus Internetworking Devices 300
Optimization Features on Campus Internetworking Devices 302
Example of a Campus Network Design 303
Background Information for the Campus Network Design Project 303
Business Goals 304
Technical Goals 304
Network Applications 305
User Communities 306
Data Stores (Servers) 307
Current Network at WVCC 307
Traffic Characteristics of Network Applications 310
Summary of Traffic Flows 311
Performance Characteristics of the Current Network 312
Network Redesign for WVCC 313
Optimized IP Addressing and Routing for the Campus Backbone 313
Wireless Network 314
Improved Performance and Security for the Edge of the Network 315
Summary 316
Review Questions 317
Design Scenario 317
Chapter 11 Selecting Technologies and Devices for Enterprise Networks 319
Remote-Access Technologies 320
PPP 321
Multilink PPP and Multichassis Multilink PPP 321
Password Authentication Protocol and Challenge Handshake
Authentication Protocol 322
Cable Modem Remote Access 323
Challenges Associated with Cable Modem Systems 324
Digital Subscriber Line Remote Access 325
Other DSL Implementations 326
PPP and ADSL 326
Selecting Remote-Access Devices for an Enterprise
Network Design 327
Selecting Devices for Remote Users 327
Selecting Devices for the Central Site 328
WAN Technologies 328
Systems for Provisioning WAN Bandwidth 329
Leased Lines 330
Synchronous Optical Network 331
Frame Relay 332
Frame Relay Hub-and-Spoke Topologies and Subinterfaces 333
Frame Relay Congestion Control Mechanisms 335
Frame Relay Traffic Control 335
Frame Relay/ATM Interworking 336
ATM 337
Ethernet over ATM 337
Metro Ethernet 338
Selecting Routers for an Enterprise WAN Design 339
Selecting a WAN Service Provider 340
Example of a WAN Design 341
Background Information for the WAN Design Project 341
Business and Technical Goals 342
Network Applications 343
User Communities 343
Data Stores (Servers) 344
Current Network 344
Traffic Characteristics of the Existing WAN 345
WAN Design for Klamath Paper Products 346
Summary 348
Review Questions 349
Design Scenario 349
Summary for Part III 350
Part IV Testing, Optimizing, and Documenting Your Network Design
Chapter 12 Testing Your Network Design 353
Using Industry Tests 354
Building and Testing a Prototype Network System 355
Determining the Scope of a Prototype System 355
Testing a Prototype on a Production Network 356
Writing and Implementing a Test Plan for Your Network Design 357
Developing Test Objectives and Acceptance Criteria 357
Determining the Types of Tests to Run 358
Documenting Network Equipment and Other Resources 359
Writing Test Scripts 360
Documenting the Project Timeline 361
Implementing the Test Plan 361
Tools for Testing a Network Design 362
Types of Tools 362
Examples of Network Testing Tools 363
CiscoWorks Internetwork Performance Monitor 364
WANDL Network Planning and Analysis Tools 364
OPNET Technologies 364
Ixia Tools 365
NetIQ Voice and Video Management Solution 365
NetPredict’s NetPredictor 365
Summary 366
Review Questions 366
Design Scenario 366
Chapter 13 Optimizing Your Network Design 367
Optimizing Bandwidth Usage with IP Multicast Technologies 368
IP Multicast Addressing 369
Internet Group Management Protocol 370
Multicast Routing Protocols 370
Distance Vector Multicast Routing Protocol 371
Protocol Independent Multicast 371
Reducing Serialization Delay 372
Link-Layer Fragmentation and Interleaving 373
Compressed Real-Time Transport Protocol 374
Optimizing Network Performance to Meet Quality of Service Requirements 374
IP Precedence and Type of Service 375
IP Differentiated Services Field 376
Resource Reservation Protocol 377
Common Open Policy Service Protocol 379
Classifying LAN Traffic 379
Cisco IOS Features for Optimizing Network Performance 380
Switching Techniques 380
Classic Methods for Layer 3 Packet Switching 381
NetFlow Switching 382
Cisco Express Forwarding 382
Queuing Services 383
First-In, First-Out Queuing 383
Priority Queuing 384
Custom Queuing 384
Weighted Fair Queuing 385
Class-Based Weighted Fair Queuing 386
Low-Latency Queuing 387
Random Early Detection 388
Weighted Random Early Detection 388
Traffic Shaping 389
Committed Access Rate 389
Summary 389
Review Questions 390
Design Scenario 391
Chapter 14 Documenting Your Network Design 393
Responding to a Customer’s Request for Proposal 394
Contents of a Network Design Document 395
Executive Summary 396
Project Goal 396
Project Scope 396
Design Requirements 397
Business Goals 397
Technical Goals 398
User Communities and Data Stores 399
Network Applications 399
Current State of the Network 399
Logical Design 400
Physical Design 400
Results of Network Design Testing 401
Implementation Plan 401
Project Schedule 402
Project Budget 403
Return on Investment 403
Design Document Appendix 404
Summary 404
Review Questions 405
Design Scenario 405
Glossary 407