Top-Down Network Design

Cisco Press
Priscilla Oppenheimer  
Total pages
August 2010
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Top-Down Network Design
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Top-Down Network Design, 3rd Edition presents a systematic, fully practical approach to designing networks.

Thoroughly updated for today's newest technical and business trends, it covers all facets of enterprise network design and all elements of modern enterprise networks. The authors' innovative top-down approach starts by focusing on applications and user requirements, and only then turns to technology selection. Readers will discover how to systematically analyse business and technical requirements, and then select topologies and technologies that reflect this analysis. The authors walk through designing campus networks, data centers, remote access, and wide-area connectivity, and designing for security in an era of wireless networks and mobile users. They also present detailed coverage of performance, reliability, and scalability.

This edition includes new coverage of designing networks that comply with IT Service Management processes, as well as an updated glossary. It also adds chapter-ending essay questions and design scenarios for readers who want to test their understanding of key concepts.


  • Presents an up-to-date, end-to-end design process for creating networks with maximum performance, security, scalability, and support for ITSM management processes
  • Focuses on supporting complex collaboration and the extensive use of video
  • Reflects new business models in areas ranging from bioinformatics and electronic healthcare to renewable energy and high-tech entertainment
  • A brand-new Third Edition of the best-selling, authoritative guide to designing networks that fully align with business goals
  • New to this Edition

    This Third Edition includes updated and expanded material on wireless networks, virtual private networks (VPN), network security, network redundancy, modularity in network designs, dynamic addressing for IPv4 and IPv6, Ethernet scalability options (including 10-Gbps Ethernet, Metro Ethernet, and Long-Reach Ethernet), and networks that carry voice and data traffic. In addition students will learn how to build networks that can support real-time video, collaborative computing, and social networking tools. Every chapter now includes a set of essay questions and design scenarios to give students a chance to practice what they have learned.

    Table of Contents


    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

    Back Cover

    Top-Down Network Design

    Third Edition


    Priscilla Oppenheimer


    A systems analysis approach to enterprise network design


    The authoritative book on designing networks that align with business goals


    Top-Down Network Design, Third Edition, is a practical and comprehensive guide to designing enterprise networks that are reliable, secure, and scalable. The book uses a top-down approach to help you focus first on applications and user requirements before selecting devices, cabling, and other technologies to implement the network. The book takes you through an explanation of how to design networks that align with business goals so that the network can keep pace with changing user requirements.


    This new edition provides a comprehensive look at enterprise network design and the different modules of an enterprise network. Using illustrations and real-world examples, the book covers campus network design, wireless networks, remote access, and wide-area connectivity. You learn how to analyze business and technical requirements and select topologies and technologies that are based on that analysis. A major focus is on security as network users become more mobile. You also develop an understanding of network performance factors and methods for building reliable networks that can scale as traffic loads increase.


    This Third Edition includes updated and expanded material on wireless networks, virtual private networks (VPN), network security, network redundancy, modularity in network designs, dynamic addressing for IPv4 and IPv6, Ethernet scalability options (including 10-Gbps Ethernet, Metro Ethernet, and Long-Reach Ethernet), and networks that carry voice and data traffic. In addition you will learn how to build networks that can support real-time video, collaborative computing, and social networking tools and that adhere to the Cisco SAFE Security Reference Architecture.


    Every chapter now includes a set of essay questions and design scenarios to give you a chance to practice what you have learned. The book also has a companion website at, which includes updates to the book, links to white papers, and supplemental information about design resources.


    • Learn a network design process that results in networks that perform well, provide security, and scale to meet growing demands for bandwidth
    • Develop network designs that provide the high bandwidth and low delay required for real-time applications such as multimedia, distance learning, videoconferencing, teleprescene, virtual communities, and IP telephony
    • Master techniques for checking the health of an existing network to develop a baseline for measuring performance of a new network design
    • Explore solutions for meeting QoS requirements, including IETF controlled-load and guaranteed services, IP multicast, and advanced switching, queuing, and routing algorithms
    • Identify the advantages and disadvantages of various switching and routing protocols, including Rapid Spanning Tree Protocol (RSTP), IEEE 802.1Q, EIGRP, OSPF, and BGP4


    This book is part of the Networking Technology Series from Cisco Press‚ which offers networking professionals valuable information for constructing efficient networks, understanding new technologies, and building successful careers.


    Category: Networking

    Covers:  Network Design



    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.