Top-Down Network Design

Top-Down Network Design Third Edition Priscilla Oppenheimer Cisco Press 800 East 96th Street Indianapolis, IN 46240

vi Тор-Down Network Design 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

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 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

Тор-Down Network Design 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

ix 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

x Тор-Down Network Design 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 Controiled-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 Que stions 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

xi 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

xii Тор-Down Network Design 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

xiii 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 Тор-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

xiv Тор-Down Network Design 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

XV 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 281 Chapter 10 Selecting Technologies and Devices for Campus Networks 283 LAN Cabling Plant Design 284 Cabling Topologies 284 Building-Cabling Topologies 285

xvi Тор-Down Network Design 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 Re view Que stions 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

xvii 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

xviii Тор-Down Network Design Part IV Testing, Optimizing, and Documenting Your Network Design 351 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 NetlQ 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

xix 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

xx Тор-Down Network Design 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 Index 435