Top-Down 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.

• IntroductionPart I Identifying Your Customer's Needs and GoalsChapter 1 Analyzing Business Goals and Constraints 3Using a Top-Down Network Design Methodology 3Using a Structured Network Design Process 5Systems Development Life Cycles 6Plan Design Implement Operate Optimize (PDIOO) Network Life Cycle 7Analyzing Business Goals 8Working with Your Client 8Changes in Enterprise Networks 10Networks Must Make Business Sense 10Networks Offer a Service 11The Need to Support Mobile Users 12The Importance of Network Security and Resiliency 12Typical Network Design Business Goals 13Identifying the Scope of a Network Design Project 14Identifying a Customer's Network Applications 16Analyzing Business Constraints 19Politics and Policies 19Budgetary and Staffing Constraints 20Project Scheduling 21Business Goals Checklist 22Summary 23Review Questions 23Design Scenario 24Chapter 2 Analyzing Technical Goals and Tradeoffs 25Scalability 25Planning for Expansion 26Expanding Access to Data 26Constraints on Scalability 27Availability 27Disaster Recovery 28Specifying Availability Requirements 29Five Nines Availability 30The Cost of Downtime 31Mean Time Between Failure and Mean Time to Repair 31Network Performance 32Network Performance Definitions 33Optimum Network Utilization 34Throughput 35Throughput of Internetworking Devices 36Application Layer Throughput 37Accuracy 38Efficiency 39Delay and Delay Variation 40Causes of Delay 41Delay Variation 43Response Time 44Security 44Identifying Network Assets 45Analyzing Security Risks 46Reconnaissance Attacks 47Denial-of-Service Attacks 48Developing Security Requirements 48Manageability 49Usability 50Adaptability 50Affordability 51Making Network Design Tradeoffs 52Technical Goals Checklist 54Summary 55Review Questions 56Design Scenario 56Chapter 3 Characterizing the Existing Internetwork 59Characterizing the Network Infrastructure 59Developing a Network Map 60Characterizing Large Internetworks 60Characterizing the Logical Architecture 62Developing a Modular Block Diagram 64Characterizing Network Addressing and Naming 64Characterizing Wiring and Media 65Checking Architectural and Environmental Constraints 68Checking a Site for a Wireless Installation 69Performing a Wireless Site Survey 70Checking the Health of the Existing Internetwork 71Developing a Baseline of Network Performance 72Analyzing Network Availability 73Analyzing Network Utilization 73Measuring Bandwidth Utilization by Protocol 75Analyzing Network Accuracy 76Analyzing Errors on Switched Ethernet Networks 77Analyzing Network Efficiency 79Analyzing Delay and Response Time 80Checking the Status of Major Routers, Switches, and Firewalls 82Network Health Checklist 83Summary 84Review Questions 84Hands-On Project 85Design Scenario 85Chapter 4 Characterizing Network Traffic 87Characterizing Traffic Flow 87Identifying Major Traffic Sources and Stores 87Documenting Traffic Flow on the Existing Network 89Characterizing Types of Traffic Flow for New Network Applications 90Terminal/Host Traffic Flow 91Client/Server Traffic Flow 91Peer-to-Peer Traffic Flow 93Server/Server Traffic Flow 94Distributed Computing Traffic Flow 94Traffic Flow in Voice over IP Networks 94Documenting Traffic Flow for New and Existing Network Applications 95Characterizing Traffic Load 96Calculating Theoretical Traffic Load 97Documenting Application-Usage Patterns 99Refining Estimates of Traffic Load Caused by Applications 99Estimating Traffic Load Caused by Routing Protocols 101Characterizing Traffic Behavior 101Broadcast/Multicast Behavior 101Network Efficiency 102Frame Size 103Windowing and Flow Control 103Error-Recovery Mechanisms 104Characterizing Quality of Service Requirements 105ATM QoS Specifications 106Constant Bit Rate Service Category 107Real-time Variable Bit Rate Service Category 107Non-real-time Variable Bit Rate Service Category 107Unspecified Bit Rate Service Category 108Available Bit Rate Service Category 108Guaranteed Frame Rate Service Category 108IETF Integrated Services Working Group QoS Specifications 109Controlled-Load Service 110Guaranteed Service 110IETF Differentiated Services Working Group QoS Specifications 111Grade of Service Requirements for Voice Applications 112Documenting QoS Requirements 113Network Traffic Checklist 114Summary 114Review Questions 114Design Scenario 115Summary for Part I 115Part II Logical Network Design Chapter 5 Designing a Network Topology 119Hierarchical Network Design 120Why Use a Hierarchical Network Design Model? 121Flat Versus Hierarchical Topologies 122Flat WAN Topologies 122Flat LAN Topologies 123Mesh Versus Hierarchical-Mesh Topologies 124Classic Three-Layer Hierarchical Model 125Core Layer 127Distribution Layer 127Access Layer 128Guidelines for Hierarchical Network Design 128Redundant Network Design Topologies 130Backup Paths 131Load Sharing 132Modular Network Design 133Cisco SAFE Security Reference Architecture 133Designing a Campus Network Design Topology 135Spanning Tree Protocol 135Spanning Tree Cost Values 136Rapid Spanning Tree Protocol 137RSTP Convergence and Reconvergence 138Selecting the Root Bridge 139Scaling the Spanning Tree Protocol 140Virtual LANs 141Fundamental VLAN Designs 142Wireless LANs 144Positioning an Access Point for Maximum Coverage 145WLANs and VLANs 146Redundant Wireless Access Points 146Redundancy and Load Sharing in Wired LANs 147Server Redundancy 148Workstation-to-Router Redundancy 150Hot Standby Router Protocol 152Gateway Load Balancing Protocol 153Designing the Enterprise Edge Topology 153Redundant WAN Segments 153Circuit Diversity 154Multihoming the Internet Connection 154Virtual Private Networking 157Site-to-Site VPNs 158Remote-Access VPNs 159Service Provider Edge 160Secure Network Design Topologies 162Planning for Physical Security 162Meeting Security Goals with Firewall Topologies 162Summary 163Review Questions 165Design Scenario 165Chapter 6 Designing Models for Addressing and Numbering 167Guidelines for Assigning Network Layer Addresses 168Using a Structured Model for Network Layer Addressing 168Administering Addresses by a Central Authority 169Distributing Authority for Addressing 170Using Dynamic Addressing for End Systems 170IP Dynamic Addressing 171IP Version 6 Dynamic Addressing 174Zero Configuration Networking 175Using Private Addresses in an IP Environment 175Caveats with Private Addressing 177Network Address Translation 177Using a Hierarchical Model for Assigning Addresses 178Why Use a Hierarchical Model for Addressing and Routing? 178Hierarchical Routing 179Classless Interdomain Routing 179Classless Routing Versus Classful Routing 180Route Summarization (Aggregation) 181Route Summarization Example 182Route Summarization Tips 183Discontiguous Subnets 183Mobile Hosts 184Variable-Length Subnet Masking 185Hierarchy in IP Version 6 Addresses 186Link-Local Addresses 187Global Unicast Addresses 188IPv6 Addresses with Embedded IPv4 Addresses 189Designing a Model for Naming 189Distributing Authority for Naming 190Guidelines for Assigning Names 191Assigning Names in a NetBIOS Environment 192Assigning Names in an IP Environment 193The Domain Name System 193Dynamic DNS Names 194IPv6 Name Resolution 195Summary 195Review Questions 196Design Scenario 197Chapter 7 Selecting Switching and Routing Protocols 199Making Decisions as Part of the Top-Down Network Design Process 200Selecting Switching Protocols 201Switching and the OSI Layers 202Transparent Bridging 202Selecting Spanning Tree Protocol Enhancements 203PortFast 204UplinkFast and BackboneFast 204Unidirectional Link Detection 205LoopGuard 206Protocols for Transporting VLAN Information 207IEEE 802.1Q 207Dynamic Trunk Protocol 208VLAN Trunking Protocol 208Selecting Routing Protocols 209Characterizing Routing Protocols 209Distance-Vector Routing Protocols 210Link-State Routing Protocols 212Routing Protocol Metrics 214Hierarchical Versus Nonhierarchical Routing Protocols 214Interior Versus Exterior Routing Protocols 214Classful Versus Classless Routing Protocols 214Dynamic Versus Static and Default Routing 215On-Demand Routing 216Scalability Constraints for Routing Protocols 216Routing Protocol Convergence 217IP Routing 218Routing Information Protocol 218Enhanced Interior Gateway Routing Protocol 219Open Shortest Path First 221Intermediate System-to-Intermediate System 224Border Gateway Protocol 225Using Multiple Routing Protocols in an Internetwork 225Routing Protocols and the Hierarchical Design Model 226Redistribution Between Routing Protocols 227Integrated Routing and Bridging 229A Summary of Routing Protocols 230Summary 231Review Questions 231Design Scenario 232Chapter 8 Developing Network Security Strategies 233Network Security Design 233Identifying Network Assets 234Analyzing Security Risks 234Analyzing Security Requirements and Tradeoffs 235Developing a Security Plan 235Developing a Security Policy 236Components of a Security Policy 237Developing Security Procedures 237Maintaining Security 237Security Mechanisms 238Physical Security 238Authentication 239Authorization 239Accounting (Auditing) 240Data Encryption 240Public/Private Key Encryption 241Packet Filters 243Firewalls 244Intrusion Detection and Prevention Systems 244Modularizing Security Design 245Securing Internet Connections 245Securing Public Servers 246Securing E-Commerce Servers 247Securing Remote-Access and VPNs 248Securing Remote-Access Technologies 248Securing VPNs 249Securing Network Services and Network Management 250Securing Server Farms 251Securing User Services 252Securing Wireless Networks 253Authentication in Wireless Networks 254Data Privacy in Wireless Networks 258Summary 261Review Questions 261Design Scenario 262Chapter 9 Developing Network Management Strategies 263Network Management Design 263Proactive Network Management 264Network Management Processes 264Fault Management 265Configuration Management 266Accounting Management 266Performance Management 266Security Management 268Network Management Architectures 269In-Band Versus Out-of-Band Monitoring 270Centralized Versus Distributed Monitoring 270Selecting Network Management Tools and Protocols 271Selecting Tools for Network Management 271Simple Network Management Protocol 271Management Information Bases (MIB) 272Remote Monitoring (RMON) 273Cisco Discovery Protocol 274Cisco NetFlow Accounting 276Estimating Network Traffic Caused by Network Management 276Summary 277Review Questions 278Design Scenario 278Summary for Part II 279Part III Physical Network Design Chapter 10 Selecting Technologies and Devices for Campus Networks 283LAN Cabling Plant Design 284Cabling Topologies 284Building-Cabling Topologies 285Campus-Cabling Topologies 285Types of Cables 285LAN Technologies 289Ethernet Basics 290Ethernet and IEEE 802.3 290Ethernet Technology Choices 291Half-Duplex and Full-Duplex Ethernet 292100-Mbps Ethernet 292Gigabit Ethernet 29310-Gbps Ethernet 295Selecting Internetworking Devices for a Campus Network Design 299Criteria for Selecting Campus Internetworking Devices 300Optimization Features on Campus Internetworking Devices 302Example of a Campus Network Design 303Background Information for the Campus Network Design Project 303Business Goals 304Technical Goals 304Network Applications 305User Communities 306Data Stores (Servers) 307Current Network at WVCC 307Traffic Characteristics of Network Applications 310Summary of Traffic Flows 311Performance Characteristics of the Current Network 312Network Redesign for WVCC 313Optimized IP Addressing and Routing for the Campus Backbone 313Wireless Network 314Improved Performance and Security for the Edge of the Network 315Summary 316Review Questions 317Design Scenario 317Chapter 11 Selecting Technologies and Devices for Enterprise Networks 319Remote-Access Technologies 320PPP 321Multilink PPP and Multichassis Multilink PPP 321Password Authentication Protocol and Challenge HandshakeAuthentication Protocol 322Cable Modem Remote Access 323Challenges Associated with Cable Modem Systems 324Digital Subscriber Line Remote Access 325Other DSL Implementations 326PPP and ADSL 326Selecting Remote-Access Devices for an EnterpriseNetwork Design 327Selecting Devices for Remote Users 327Selecting Devices for the Central Site 328WAN Technologies 328Systems for Provisioning WAN Bandwidth 329Leased Lines 330Synchronous Optical Network 331Frame Relay 332Frame Relay Hub-and-Spoke Topologies and Subinterfaces 333Frame Relay Congestion Control Mechanisms 335Frame Relay Traffic Control 335Frame Relay/ATM Interworking 336ATM 337Ethernet over ATM 337Metro Ethernet 338Selecting Routers for an Enterprise WAN Design 339Selecting a WAN Service Provider 340Example of a WAN Design 341Background Information for the WAN Design Project 341Business and Technical Goals 342