Top-Down Network Design / Edition 3

by Priscilla Oppenheimer

Overview

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

Product Details

ISBN-13:	9781587202834
Publisher:	Pearson Education
Publication date:	08/24/2010
Series:	Networking Technology
Pages:	480
Product dimensions:	7.40(w) x 9.20(h) x 1.20(d)

About the Author

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.

Read an Excerpt

Chapter 5: Designing a Network Topology

Designing a backup path that has the same capacity as the primary path can beexpensive and is only appropriate if the customer's business requirements dictate abackup path with the same performance characteristics as the primary path.

If switching to the backup path requires manual reconfiguration of any components,then Users will notice disruption. For mission-critical applications, disruption isprobably not acceptable. An automatic fallover is necessary for mission-criticalapplications. BY using redundant, partial-mesh network designs, you can speedautomatic recovery time when a link falls.

One other important consideration with backup paths is that they must be tested.Sometimes network designers develop backup solutions that are never tested until acatastrophe happens. When the catastrophe occurs, the backup links do not work. Insome network designs, the backup links are used for load balancing as well asredundancy. This has the advantage that the backup path is a tested solution that isregularly used and monitored as a part of day-to-day operations. Load balancing isdiscussed in more detail in the next section.

Load Balancing

The primary purpose of redundancy is to meet availability requirements. A secondarygoal is to improve performance by supporting load balancing across parallel links.

Load balancing must be planned and in some cases configured. Some protocols do notsupport load balancing by default. For example, when running Novell's Routing Protocol(RIP), an Internetwork Packet Exchange (IPX) router can remember only one route to aremote network. You can change this behavior on a Ciscorouter by using the ipx maximum-paths command.

In ISDN environments, You can facilitate load balancing by configuring channelaggregation. Channel aggregation on means that a router can automatically bring upmultiple ISDN B channels as bandwidth requirements increase. The Multilink Point-to-Point Protocol (MPPP) is an Internet Engineering Task Force (IETF) standard for ISDN B-channel aggregation. MPPP ensures that packets arrive in sequence at the receivingrouter. To accomplish this, data is encapsulated within the Point-to-point Protocol (PPP)and datagrams are given a sequence number. At the receiving router, PPP uses thesequence number to re-create the original data stream. Multiple channels appear as onelogical link to upper-layer protocols.Most vendor's implementations of IP routing protocols support load balancing acrossparallel links that have equal cost. (Cost values are used by routing protocols todetermine the most favorable path to a destination. Depending on the routing protocol,cost can be based on hop count, bandwidth, delay, or other factors.) Cisco supports loadbalancing across six parallel paths. With the IGRP and Enhanced [GRP protocols, Ciscosupports load balancing even when the paths do not have the same bandwidth (which isthe main metric used for measuring cost for those protocols). Using a feature calledvariance, IGRP and Enhanced IGRP can load balance across paths that do not haveprecisely the same aggregate bandwidth. Cost, metrics, and variance are discussed inmore detail in Chapter 7, "Selecting Bridging, Switching, and Routing Protocols."

Some routing protocols base cost on the number of hops to a particular destinationsThese routing protocols load balance over unequal bandwidth paths as long as thehop count is equal. Once a slow link becomes saturated, however higher capacitylinks cannot be filled. This is called Pinhole congestion. Pinhole congestion can be avoided by designing equal bandwidth links within one layer of the hierarchyusing a routing protocol that bases cost on bandwidth and has the variance feature.

Load balancing can be affected by advanced switching (forwarding) mechanismsimplemented in routers. Advanced switching processes often cache the path to remotedestinations to allow fast forwarding of subsequent packets to that destination. (Thecache obviates the need for the router CPU to look in the routing table for a path. Theresult of caching is that all packets destined to a particular destination take the same path.In this case, load balancing occurs across traffic flows to different destinations, but not ona packet-per-packet basis. Some newer technologies, such as Cisco Express Forwarding(CEF), can be configured to do packet-per-packet or destination-per-destination loadbalancing. Chapter 12, "Optimizing Your Network Design," covers CEF in more detail.

DESIGNING A CAMPUS NETWORK DESIGN TOPOLOGY

Campus network design topologies should meet a customer's goals for availability andperformance by featuring small broadcast domains, redundant distribution-laversegments, mirrored servers, and multiple ways for a workstation to reach a router for off-net communications. Campus networks should be designed using a hierarchical model sothat the network offers good performance, maintainability, and scalability.

Virtual LANs

A virtual LAN (VLAN) is an emulation of a standard LAN that allows data transfer totake place without the traditional physical restraints placed on a network. A networkadministrator can use management software to group users into a VLAN so they cancommunicate as if they were attached to the same wire, when in fact they are located ondifferent physical LAN segments. Because VLANs are based on logical instead ofphysical connections, they are very flexible.

Companies that are growing quickly cannot guarantee that employees working on thesame project will be located together. With VLANs, the physical location of a user doesnot matter. A network administrator can assign a user to a VLAN regardless of the user'slocation. In theory, VLAN assignment can be based on applications, protocols,performance requirements, security requirements, traffic-loading characteristics, or otherfactors.

VLANs allow a large flat network to be divided into subnets. This feature can be used todivide up broadcast domains. Instead of flooding all broadcasts out every port, a VLAN-enabled switch can flood a broadcast out only the ports that are part of the I same subnetas the sending station.

In the past, some companies implemented large switched campus networks with fewrouters. The goals were to keep costs down by using switches instead of routers, andprovide good performance because presumably switches were faster than routers. Withoutthe router capability of containing broadcast traffic, however, the companies neededVLANs. VLANs allow the large flat network to be divided into subnets. A router (or arouting module within a switch) was still needed for inter-subnet communication.

As routers become as fast as switches and Layer-3 functionality is added to switches,fewer companies will implement large, flat, switched networks, and there will be less of aneed for VLANs.

VLAN-based networks can be hard to manage and optimize. Also, when a VLAN isdispersed across many physical networks, traffic must flow to each of those networks,which affects the performance of the networks and adds to the capacity requirements oftrunk networks that connect VLANs....

Table of Contents

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