Top-Down Network Design

Cisco Press
Priscilla Oppenheimer  
Total pages
August 2010
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Top-Down Network Design
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Network usage is continuing to accelerate as enterprise network users communicate via video-conferencing, develop products more collaboratively, and rely more heavily on networked tools. Top-Down Network Design, Third Edition presents a systematic, fully practical approach to designing networks that will keep pace with these changes. 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 analyze 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. Graphics are used extensively throughout to clarify concepts and present examples This Third 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. The book also has a companion website at, which includes PowerPoint slides of the figures in the book, updates to the book, links to white papers, and supplemental information about design resources.

    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

        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


    9781587202834    TOC    8/2/2010


    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.