Cisco Press 2003 - OSPF Network Design Solutions Second Edition

Contents at a Glance Introduction xix Part I OSPF Fundamentals and Communication 3 Chapter 1 Networking and Routing Fundamentals 5 Chapter 2 Introduction to OSPF 47 Chapter 3 OSPF Commun

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Manager, Marketing Communications, Cisco Systems Scott Miller

Daniel Golding, John Hammond, Cary Riddock

About the Author

Thomas M Thomas II is a self-proclaimed Network Emergency Repair Dude, or NERD for short, and a country boy who is CCIE No 9360 as well as being a certified Cisco Systems instructor and holding CCNP, CCDA, and CCNA certifications and claims he never works because he loves what he does Tom is the founder of NetCerts.com (now CCPrep.com) and the International Network Resource Group (www.inrgi.net ) where he remains on the board

of directors in an advisory capacity, providing vision and focus He was previously an Instructor for Chesapeake Computer Consultants, Inc (CCCI), and a course developer for Cisco Systems He has also authored the first edition

of OSPF Network Design Solutions and a variety of other networking books designed to help his fellow engineers

Tom is currently working as a senior network consultant designing and implementing Voice-over-IP and Data networks wherever he can as a part of US Networks, Inc (www.usnetworksinc.com) Tom currently lives in Raleigh, NC, with his family, and although he is not in the country, he humorously observes that you can see it from his home.

About the Technical Reviewers

Henry Benjamin, CCIE No 4695, holds three CCIE certifications (Routing and Switching, ISP Dial, and tion and Services) Formerly with the Cisco Systems CCIE global team, Henry is now an independent consultant for

Communica-a lCommunica-arge security firm in AustrCommunica-aliCommunica-a He hCommunica-as served Communica-as Communica-a proctor for the CCIE LCommunica-ab exCommunica-ams Communica-and is the Communica-author of CCNP

Practical Studies: Routing from Cisco Press and CCIE Routing and Switching Exam Cram from Coriolis.

Matthew H Birkner, CCIE No 3719, is a technical leader at Cisco Systems, specializing in IP and MPLS network

design He has influenced multiple large carrier and enterprise designs worldwide Matt has spoken at Cisco Networkers

on MPLS VPN technologies in both the United States and EMEA over the past few years Matt, a “Double CCIE,”

authored the Cisco Press book, Cisco Internetwork Design Matt holds a B.S.E.E from Tufts University, where he

majored in electrical engineering.

Rick Burts, CCIE No 4615, has over 20 years experience with computers and computer networks Rick is a certified

Cisco Systems instructor and a CCIE (Routing/Switching) He has taught a variety of Cisco courses and helped develop an OSPF course for Mentor Technologies Rick is a consultant and has helped many customers with OSPF as their network routing protocol He is a senior consultant with Chesapeake NetCraftsmen (www.netcraftsmen.net) In his current position, Rick deals with network design, implementation, and troubleshooting issues and teaches a few courses.

Daniel L Golding is peering manager in America Online’s Internet Architecture group Dan is responsible for

ensuring worldwide Internet connectivity for all AOL Time Warner subscribers and properties His particular areas

of expertise include internetwork peering and routing policy design He has a long history of involvement with various Internet service providers, particularly in the area of backbone engineering Dan is also a frequent speaker at North American Network Operator’s Group (NANOG) meetings and has been a network engineer for over six years.

John Hammond has been an instructor and course developer for Juniper Networks for the past two years Prior to

that he was a member of the teaching staff of Chesapeake Computer Consultants, Inc., a Cisco Training Partner John has been involved in many aspects of networks since 1990.

Cary Riddock, CCNP, CSS1, has worked as an network engineer for some of the largest companies in Houston,

Texas and Central Florida over the last six years He is very active in the IT Security Field and is currently pursuing

CCSP and CISSP certifications His resume includes co-authoring MCNS for Cisco Press and is a contributing

author for various network security publications

Dedications

I want to dedicate this book to my family for their ever-faithful support and understanding during the many nights and weekends I spent writing An extra special thank you goes to my wife Rose, daughter Rebekah, and son Daniel who never voiced anything but encouragement and support

Without the support of my family and their faith in me I would never have been able to completely rewrite this book.

I had my faith in the Lord and the knowledge that my family knew I could improve upon my book in this new edition

Writing this book allowed me to assemble a team of technical professionals who have helped me make this book more than I thought possible I had the privilege to be a part of an awesome team during this time Thank you all for your insight and friendship.

I have to recognize the extraordinary group of publishing professionals who helped guide me through the process: Amy Moss, a true and dear friend of many years now; and Chris Cleveland who is always busy but always has time

to help me.

Contents at a Glance

Introduction xix

Part I OSPF Fundamentals and Communication 3

Chapter 1 Networking and Routing Fundamentals 5

Chapter 2 Introduction to OSPF 47

Chapter 3 OSPF Communication 103

Part II OSPF Routing and Network Design 161

Chapter 4 Design Fundamentals 163

Chapter 5 Routing Concepts and Configuration 225

Chapter 6 Redistribution 339

Chapter 7 Summarization 405

Part III OSPF Implementation, Troubleshooting, and Management 439 Chapter 8 Managing and Securing OSPF Networks 441

Chapter 9 Troubleshooting OSPF 533

Chapter 10 BGP and MPLS in an OSPF Network 655

Part IV Additional OSPF Resources 707

Appendix A OSPF RFCs 705

Contents

Introduction xix

Part I OSPF Fundamentals and Communication 3

Chapter 1 Networking and Routing Fundamentals 5

Foundations of Networking 6 Why Was the OSI Reference Model Needed? 6 Characteristics of the OSI Layers 7

Understanding the Seven Layers of the OSI Reference Model 9 Upper Layers 9

Layer 7—Application 9 Layer 6—Presentation 10 Layer 5—Session 10 Lower Layers 10 Layer 4—Transport 10

Layer 2—Data Link 11 Layer 1—Physical 12 OSI Reference Model Layers and Information Exchange 13 Headers, Trailers, and Data 13

TCP/IP Protocol Suite 14 TCP/IP Functions 15 TCP Overview 15

IP Overview 16 Types of Network Topologies 16 Local-Area Networks 16 Wide-Area Networks 17

IP Addressing 21 Class A Addresses 22 Class B Addresses 22 Class C Addresses 23 Class D Addresses 23 Class E Addresses 23 How IP Addresses Are Used 24 Role of IP Addresses 27 How IP Addresses Are Read 27

IP Subnet Addressing 28 Subnet Masking 29 Subnetting Restrictions 31 Explaining the Need for VLSM and CIDR 31 Route Summarization 33

Classful Routing 34 Impact of Classful Routing 34 Classless Routing 34

IP Classless 39 CIDR Translation Table 39 Manually Computing the Value of a CIDR IP Prefix 40 Case Study: VLSMs 41

Route Aggregation 42

Chapter 2 Introduction to OSPF 47

What Is a Routing Protocol? 48 Basic Routing Protocol Operation 50 Link-State Versus Distance Vector Routing Protocols 51 Link-State Routing Protocols 52

OSPF Characteristics 53 Integrated Intermediate System-to-Intermediate System 54 Distance Vector Routing Protocols 55

Routing Information Protocol Characteristics 56 Conclusion 56

Selecting a Routing Protocol 57 Operational Considerations 57 Protocols Supported 57 Routing Hierarchies 58

IP Address Management 59

IP Encapsulation Support 59 Available Resources 59 Technical Considerations 60 Fast Convergence 60 Routing Updates 61

Load Sharing 61 Metrics 61 Scalability 62 Physical Media Support 62 Extensibility 62

Business Considerations 62 Standards 63

Multivendor Environments 63 Proven Technology 63 SPF Overview 63

SPF in Operation 64 SPF Functions 68 Full and Partial SPF Calculations 70 Verifying SPF Operation 70 OSPF Routing Hierarchy 71 Hierarchical Network Design Techniques 71 Routing Types Within an OSPF Network 72 Intra-Area Routing 72

Inter-Area Routing 72 External Routes 73 OSPF Areas 74 Characteristics of a Standard OSPF Area 74 Standard Area Design Rules 74

Area 0: The OSPF Backbone Area 75 Stub Areas 75

Not-So-Stubby Areas 76 OSPF Operational Environment 77 Types of OSPF Routers 77 Internal Routers 78 Area Border Routers 78 Autonomous System Boundary Routers 78 Backbone Routers 79

OSPF Network Types 79 Router Identification 80 Neighbors 81

Adjacencies 82 Neighbor Versus Adjacent OSPF Routers 82 Designated Routers 83

Case Study: Adding a New OSPF Router to a Network 85

Case Study: Developing the Link-State Database 88 Case Study: OSPF Network Evolution and Convergence 95 Configuring Loopback Interfaces 96

Enabling OSPF 96 Verifying OSPF Operation 97

Chapter 3 OSPF Communication 103

Link-State Advertisements 103 Types of LSAs 103 Type 1: Router LSAs 104 Type 2: Network LSAs 105 Type 3: ABR Summary LSAs 107

Type 5: Autonomous System External LSAs 109 Type 7: Not-So-Stubby Area LSAs 110 Type 9: Opaque LSA: Link-Local Scope 112 Type 10: Opaque LSA: Area-Local Scope 113 Type 11: Opaque LSA: Autonomous System Scope 113 LSA Operation Example 113

Link-State Database Synchronization 116 Speaking OSPF 121

Types of OSPF Packets 121 Hello Process/Protocol 122 Hello Protocol Operational Variations 124 Hello Protocol Packet Format 125 Exchange Process/Protocol 126 Flooding Process/Protocol 127 Manipulating LSAs 128

Understanding LSA Group Pacing 128 How to Configure LSA Group Pacing 130 Understanding OSPF Packet Pacing 131 Blocking LSA Flooding 131

Ignoring MOSPF LSA Packets 132 Altering LSA Retransmissions 132 Altering LSA Transmission Delay 133 Detailed Neighbor Establishment 133 Hello Protocol State Changes 133 Database Exchange State Changes 134 Case Study: OSPF Initialization 138 Case Study: Troubleshooting Neighbor Problems 149 Neighbor Stuck in Init STATE 150

Neighbor Stuck in Exstart/Exchange State 151 What’s the Solution? 156

Neighbor Stuck in 2-Way State 156

Part II OSPF Routing and Network Design 161

Chapter 4 Design Fundamentals 163

OSPF Design Guidelines 164 OSPF Design Goals 164 Functionality 165 Scalability 165 Adaptability 166 Manageability 166 Cost Effectiveness 166

Using a Stub Area 175 Example of an OSPF Network with a Hierarchical Structure 177 Step 3: Determine the Addressing and Naming Conventions 180 Public or Private Address Space 180

Plan Now for OSPF Summarization 181 Bit Splitting (Borrowing Bits) 184 Map OSPF Addresses for VLSM 184 Discontiguous Subnets 185

Step 4: Provision the Hardware 186 Step 5: Deploy Protocol and Cisco IOS Software Features 187 OSPF Features 187

Cisco IOS Software Features 188 Step 6: Implement, Monitor, and Manage the Network 189 OSPF Network Scalability 189

OSPF Network Topology 190 Area Sizing 191

Determining the Number of Areas per ABR 192 Determining the Number of Areas per Router 194 Determining the Number of Neighbors per Router 194 Selecting the Designated Router 195

Fully Meshed Versus Partially Meshed Network Topology 196 Link-State Database Size Considerations 197

Determining Router Memory Requirements 197 Router CPU Requirements 199

Bandwidth Usage 199 OSPF Security 199 Area Design Considerations 200 Area Design Overview 200 Considering Physical Proximity 201 Reducing the Area Size if Links Are Unstable 201 Ensuring Contiguous Areas 201

Using Tunable OSPF Parameters 202 Naming an Area 204

Standard Area Design 205 Golden Rules of Standard Area Design 205 Backbone Area Design 205

Backbone Design Golden Rules 206 Stub Area Design 207

Stub Area Design Golden Rules 208 Stub Area Configuration 208 Totally Stubby Areas 212 Not-So-Stubby Areas 212 NSSA Implementation Considerations 214 OSPF Virtual Links: Bane or Benefit? 215 Mending a Partitioned Area 0 215 Ensuring a Connection to Area 0 216 Golden Rules of Virtual Link Design 217 Virtual Link Configuration Example 217 OSPF Design Tools 230

Altering Neighbor Cost 230

Case Study Conclusion 239 Case Study: Designing an OSPF Network 240

Determining the Frame Relay PVC Architecture 242 Determining Multiprotocol Support 242

Determining the Traffic Flow 243 Determining the Number of Routers 244 Determining the IP Addressing Scheme 244 Determining Internet Connectivity 244 Determining Enterprise Routing Policies 244 Establishing Security Concerns 244 Implementing Your Design 245

IP Addressing 245 OSPF Area Organization 247 Specifying the OSPF Network Type 248 Implementing Authentication 248 Configuring Link Cost 249 Tuning OSPF Timers 249 Strategizing Route Redistribution 250

Chapter 5 Routing Concepts and Configuration 255

OSPF Routing Concepts 255 OSPF Cost 256

ip cost Interface Command 259 Changing the Reference Bandwidth 259 Altering OSPF Convergence 261

Hello Timers 261 Dead Timers 262 SPF Timers 262 Setting the Router ID 264 Loopback Interfaces 264 Configuring a Loopback Interface 265 Routing Loopback Interfaces 265 Configuring the Designated Router 266 Route Types 266

Which Is Better—E1 or E2 Routes? 268 Controlling Inter-Area Traffic 269 Configuring OSPF 270

Activating OSPF 271

OSPF Router Considerations 273 ABR Considerations 273 ASBR Considerations 274 Backbone Router Considerations 275 Different Network Types and OSPF 276 Configuring the Network Type 276 Broadcast Networks 277

Nonbroadcast Networks 278 Point-to-Multipoint Networks 279 Point-to-Point Networks 283

Area Configuration 284 Normal Area Configuration 285 Stub Area Configuration 289 Totally Stubby Area Configuration 294 Not-So-Stubby-Area (NSSA) Configuration 297 area default-cost Command 306

Area Range 309 Tuning OSPF Operation 313 Altering OSPF Administrative Distance 313 Load Balancing 314

Default Routes 318 Passive Interfaces 321 On-Demand Circuits 322 Implementation Considerations 324 On-Demand Configuration Examples 324 On-Demand Circuits Summary 328

Default Routes 347 default-information originate Command 348 Assigning Metrics for Redistributed Protocols 354 Using the redistribute Command to Assign a Metric 354 Using the default-metric Command to Assign a Metric 354 Configuration Example 1: Setting the Default Metric for Redistributed Routes 355 Route Tagging 359

Mutual Redistribution 360 Distribute List Concerns 361 Avoiding Redistribution Loops 364

Configuration Example 2: RIP and OSPF 366 Configuring the RIP Network 366 Adding OSPF to the Center of a RIP Network 368 Adding OSPF Areas 372

What If Mutual Redistribution Were Required? 375 Configuration Example 3: Redistributing Connected and Loopback Interfaces 376 Configuration Example 4: Redistributing OSPF and EIGRP 380

OSPF and EIGRP Mutual Redistribution 384 Using Route Maps to Protect Against Routing Loops 385 Using Route Tagging to Protect Against Routing Loops 388 Configuration Example 5: Redistributing OSPF and RIP and Tagging Routes 390 OSPF and RIP Mutual Redistribution 392

Redistributing into OSPF with Route Tagging 393 Configuration Example 6: Controlling Redistribution 396 Altering Link Cost 396

Altering Routes 397 Filtering Routes 398 Distribute Lists and OSPF 398 Chapter Summary 403

Chapter 7 Summarization with OSPF 405

Summarization with OSPF 406 Benefits of Summarization 408 Summarization Golden Rules 409 Troubleshooting Summarization 410 Types of OSPF Summarization 410 Summarize Area Routes 411 Summarize External Routes 414 Summarizations Effect on the Routing Table 418 Configuration Example 3: Subnetting with Summarization 420 Alternative Area Summarization Example 423

Using Private Addressing to Summarize? 424 Configuration Example 4: Using VLSM with Summarization 426

Final Router Example Configurations 431

Part III OSPF Implementation, Troubleshooting, and Management 439

Chapter 8 Managing and Securing OSPF Networks 441

Network Management System 451 Agents 452

Managed Devices 452 Management Information Base Overview 453

SNMP Operation Definitions 455 Network Management System Operation 456 Agent Response to NMS Request 458 Cisco’s MIB Extensions+ 459 Access Lists for SNMP 462 Multiple Community Strings 462

Network Security 466 Assessing the Need for Security 467 Golden Rules for Designing a Secure Network 467 Document Your Security Plan 468

Count the Cost 469 Identify Your Assumptions 470 Control and Limit Your Secrets 470 Remember Human Factors 471 Know Your Weaknesses 472 Limit the Scope of Access 472 Understand Your Environment 472 Limit Your Trust 472

Remember Physical Security 473 Security Is Pervasive 473 Additional Resources on Network Security 473 Securing Your OSPF Network 473

OSPF and Network Devices 474 Cisco IOS Password Encryption 474 Network Impact: User Passwords (vty and Enable) 475 Increasing SNMP Security 477

Network Data Encryption 478

OSPF Authentication 479 Benefits of OSPF Neighbor Authentication 480 When to Deploy OSPF Neighbor Authentication 481 How OSPF Authentication Works 481

Configuring OSPF Authentication in an Area 483 Configuring OSPF Authentication on a Virtual Link 489 Changing the Virtual Link Password 492

Restricting Access to Network Devices 493 Controlling Access to Network Equipment 493 Terminal Access Controller Access Control System 497 Nonprivileged Access 498

Privileged Access 498 Privilege Level Security 499 Access Lists to Restrict Access 501 User Authentication to Restrict Access 504

Case Study: IOS Secure Template 506 Case Study: Router and Firewall Deployment 518 Defending Against Attacks Directly to Network Devices 518 Controlling Traffic Flow 519

Configuring the Firewall Router 520 Defining Firewall Access Lists 520 Applying Access Lists to Interfaces 527 Configuring the Communication Server 528 Defining the Communication Server’s Access Lists 528 Applying Access Lists to Lines 529

Spoofing and Inbound Access Lists 529 Additional Firewall Security Considerations 530 File Transfer Protocol Port 530

Chapter 9 Troubleshooting OSPF 533

The Mechanics of Troubleshooting OSPF 533 Preparing for Network Failure 534 Troubleshooting Methodology 535 Step 1: Clearly Define the Problem 537 Step 2: Gather Facts 537

Step 3: Consider Possible Problems 538 Step 4: Create an Action Plan 539 Step 5: Implement the Action Plan 539 Step 6: Gather Results 539

Step 7: Reiterate the Process 540 Determining That OSPF Is Operating Properly 540 Monitoring the Operation of OSPF 541 Configuring Lookup of DNS Names 541 System Logging (SYSLOG) 543

Logging OSPF Neighbor Changes 548 OSPF Troubleshooting Commands 549 show ip ospf Command 550 show ip ospf process-id Command 553 show ip ospf interface Command 553 show ip ospf border-routers Command 555 show ip ospf database Command 556 show ip ospf database asbr-summary Command 560 show ip ospf database database-summary Command 563 show ip ospf database external Command 564

show ip ospf database network Command 566 show ip ospf database router Command 568 show ip ospf database summary Command 570 show ip ospf delete Command (Hidden) 572 show ip ospf events Command (Hidden) 575 show ip ospf flood-list Command 579

clear ip ospf counters Command 585 clear ip ospf process Command 586 clear ip ospf redistribution Command 587

When to Use debug Commands 587 How to Use debug Commands 588 Timestamping debug Output 589 Complete OSPF debug Commands 589 debug ip ospf adjacency Command 591 debug ip ospf events Command 593 debug ip ospf flood Command 595 debug ip ospf hello Command 597 debug ip ospf lsa-generation Command 598 debug ip ospf monitor Command (Hidden) 599 debug ip ospf packet Command 600

debug ip ospf retransmission Command 602 debug ip ospf spf Command 602

debug ip routing Command 614

Step 7: Reiterate the Process, If Needed, in Steps 4–7 623 Step 4: Create a New Action Plan 624

Step 5: Implement the New Action Plan 624 Step 6 Revisited: Gather Results 625 Step 7: Reiterate Steps 4–6 625 Step 6 Visited Again: Gather Results 627 Problem #2: Performance Issues 628 Step 1: Define the Problem 628 Step 2: Gather Facts 628 Step 4: Create an Action Plan 629 Step 5: Implement the Action Plan 630 Step 6: Gather Results 631

Case Study Conclusion and Design Tips 632 Case Study: OSPF Issues and Teasers 633 OSPF Error Messages 634

What Do %OSPF-4-ERRRCV Error Messages Mean? 635 What Does the Adv router not-reachable Error Message Mean? 635 OSPF Is Having Neighbor and Adjacency Problems 635

OSPF Stuck in INIT 636

OSPF Routes Missing from Routing Table 642 OSPF Routes Are in the Database but Not in the Routing Table 643

Miscellaneous Known OSPF Issues 647 Why Doesn’t My Cisco 1600 Router Recognize the OSPF Protocol? 647 Why Doesn’t My Cisco 800 Router Run OSPF 647

Why Is the ip ospf interface-retry 0 Configuration Command Added to All Interfaces? 648 How Do I Produce a Stable OSPF Network with Serial Links Flapping? 648

OSPF Routing Issues 648

Chapter 10 BGP and MPLS in an OSPF Network 655

Review of Interior Gateway Protocols and Exterior Gateway Protocols 655 Role of IGPs and EGPs in a Network 656

Introduction to BGP 660 Characteristic Overview of BGP 661 Operational Overview of BGP 662 Preventing Routing Loops 663 Types of BGP 664

BGP and OSPF Interaction 665 Routing Dependencies and Synchronization 667 Synchronization Is Good 668

Synchronization Is Bad 669 Next-Hop Reachability 671 Redistributing OSPF into BGP 673 Redistributing OSPF Internal (Intra- and Inter-Area) Routes into BGP 676 Redistributing OSPF External (Type 1 and 2) Routes into BGP 677 Redistributing Both Internal and External Routes into BGP 679 Redistributing OSPF NSSA-External Routes into BGP 679 Conclusions About BGP 680

Case Study: BGP 680 Problem Description 680

What Is the Benefit of MPLS? 686 Why Not IP Routing or ATM Switching? 686 Conventional Best Effort Routing 687

Label Structure 691 Label Placement 692 MPLS Addresses Traffic Engineering 693 Looking up the Label Path 695

Configuring OSPF and MPLS 696 Configuring MPLS 697 Verifying OSPF and MPLS Operation 701

Part IV Additional OSPF Resources 705

Appendix A Overview of the OSPF RFCs 707

Icons Used in This Book

Throughout this book, you will see the following icons used for networking devices:

The following icons are used for peripherals and other devices:

DSU/CSU

Catalyst Switch

Multilayer Switch

ATM Switch

ISDN/Frame Relay Switch

Communication Server

Macintosh

Terminal File

Server

Web Server

Cisco Works Workstation

Mainframe

Front End Processor

Cluster Controller

The following icons are used for networks and network connections:

Command Syntax Conventions

The conventions used to present command syntax in this book are the same conventions used in the Cisco IOS Software Command Reference The Command Reference describes these conventions as follows:

• Vertical bars (|) separate alternative, mutually exclusive elements.

• Square brackets [ ] indicate optional elements.

• Braces { } indicate a required choice.

• Braces within brackets [{ }] indicate a required choice within an optional element.

• Boldfaceindicates commands and keywords that are entered literally as shown In actual configuration examples and output (not general command syntax), boldface indicates commands that are manually input

by the user (such as a show command).

• Italics indicate arguments for which you supply actual values.

Network Cloud

Token Ring Token Ring Line: Ethernet

FDDI

FDDI Line: Serial

Line: Switched Serial

Introduction

OSPF is in use in numerous networks worldwide OSPF is also one of the most widely tested on cols if you choose to pursue a networking certification From a technical perspective, the overwhelming presence of OSPF ensures that almost everyone will encounter it at some point in their career A result

proto-of these facts is that everyone should understand OSPF including how it operates, how to configure it, troubleshooting, and—most importantly—how to design a network that will use OSPF You can see that everyone will be exposed to OSPF to some degree, and because it is highly likely that your family is surfing the Internet and having their packets pass over a network that is OSPF enabled, it is clear to me that they, too, might benefit from this book, so consider getting them a copy as well

Who Should Read This Book?

This book is not designed to be a general networking topics book; although, it can be used for that purpose This book is intended to tremendously increase your knowledge level with regards to OSPF Personnel responsible for understanding OSPF should read this book You might need to understand OSPF because you are a programmer, network manager, network engineer, studying for certification, and so on

How This Book Is Organized

Although this book can be read cover-to-cover, it is designed to be flexible and allow you to easily move between chapters and sections of chapters to cover just the material that you need more information on

If you do intend to read them all, the order in the book is an excellent sequence to use:

• Chapter 1, “Networking and Routing Fundamentals”—Those of us responsible for

programming, managing, maintaining, troubleshooting, and ensuring the operation of the network will appreciate this chapter as the building blocks of interworking are reviewed

• Chapter 2, “Introduction to OSPF”—This chapter helps you understand the basic types of routing protocols, their characteristics, and when it is best to use a certain protocol and uses that information to build a deeper understanding of how to implement them in your network

• Chapter 3, “OSPF Communication”—This chapter introduces you to how OSPF communicates

between routers running OSPF This chapter covers how the link-state information is then entered

into the link-state database through OSPF’s use of Link-State Advertisement (LSA) and the various internal OSPF protocols that define and allow OSPF routers to communicate

• Chapter 4, “Design Fundamentals”—The foundation of understanding the purpose for using OSPF and its operation as discussed in previous chapters is further expanded as the discussion of OSPF performance and design issues are expanded Within each of the design sections, a series of

“golden design rules” are presented These rules can help you understand the constraints and recommendations of properly designing each area within an OSPF network In many cases, examples are presented that draw upon the material presented, to further reinforce key topics and ideas

• Chapter 5, “Routing Concepts and Configuration”—This is going to be a fun chapter that will challenge you, the reader, and me, the author, to keep you interested in the different We are going

to look at all the OSPF features, knobs, and functionality that are possible

• Chapter 6, “Redistribution” and Chapter 7, “Summarization”—Redistribution and

summarization are interesting concepts, and these chapters decipher and demystify the challenges

you face when one routing algorithm is redistributed into another, when one of those protocols is

OSPF (of course), or when the OSPF routing table is optimized through summarization

• Chapter 8, “Managing and Securing OSPF Networks”—The management of your OSPF

network is just as important as the security In fact, a case could be made that proper network

management is the most important aspect of having your network operate smoothly

• Chapter 9, “Troubleshooting OSPF”—This chapter builds upon the design theories and OSPF

communication processes as discussed throughout the book prior to this chapter The basis for this

chapter is how to go about monitoring OSPF to ensure it is operating correctly and what to do if it

is not There are certain troubleshooting procedures and techniques that you can use to determine

the causes of a network problem, which are covered as well

• Chapter 10, “BGP and MPLS in an OSPF Network”—This chapter covers some of the evolving

OSPF extensions and new capabilities as OSPF grows to embrace new technologies such as

Multiprotocol Label Switching (MPLS) This chapter begins this discussion by reviewing the difference

between an IGP and an EGP routing protocol, and then looks at how OSPF interacts with BGP

P A R T

OSPF Fundamentals and

Communication

Chapter 1 Networking and Routing Fundamentals

Chapter 2 Introduction to OSPF

of the local news stations now displays the e-mail address of its reporters as they deliver the news! Is this the new economy in action, or is it just another example of too much infor-mation? At least the media are feeding on their own now!

Can you imagine modern business or life without computers, fax machines and services, e-mail, Internet commerce, automatic teller machines, remote banking, check cards, or video conferencing? Even more importantly, today’s children think that these tools are commonplace and that business cannot be done without them when they get to our age I hate to admit it, but I can clearly remember a time without the Internet and when Novell ruled the office; however, nothing stands still in our industry, and some of us have known that for quite a while

Gordon Moore of Intel made an interesting observation in 1965, just 6 years after he invented the first planar transistor He observed that the “doubling of transistor density on

a manufactured die every year” would occur Now almost 40 years later, his statement has

become known as Moore’s law, and it has continued to hold true According to Intel

There are no theoretical or practical challenges that will prevent Moore’s law from being true for another 20 years; this is another five generations of processors.

In 1995, Moore updated his prediction to indicate that transistor density would double once every two years Using Moore’s law to predict transistor density in 2012, Intel should have the capability to integrate 1 billion transistors on a production die that will be operating at

10 GHz This could result in a performance of 100,000 MIPS This represents an increase over the Pentium II processor that is similar to the Pentium II processor’s speed increase over the 386 chip That is impressive considering the sheer number of transistors on a chip that you can hold in your hand! Figure 1-1 depicts Moore’s law

Figure 1-1 Moore’s Law

OSI stands for open system interconnection, where open system refers to the specifications

surrounding the model’s structure as well as its nonproprietary public availability Anyone can build the software and hardware needed to communicate within the OSI structure If you know someone that has written a script to access information in a router, at some level,

he is following the OSI reference model

Why Was the OSI Reference Model Needed?

Before the development of the OSI reference model, the rapid growth of applications and hardware resulted in a multitude of vendor-specific models In other words, one person’s solution would not work with anyone else’s because there was no agreed-upon method, style, process, or way for different devices to interoperate In terms of future network growth and design, this rapid growth caused a great deal of concern among network engineers and designers because they had to ensure that the systems under their control could interact with every standard This concern encouraged the International Organization

of Standardization (ISO) to initiate the development of the OSI reference model

8086 80,286 80,386 80,486

P6 (Pentium Pro) P7 (Merced)

The work on the OSI reference model was initiated in the late 1970s and came to maturity

in the late 1980s and early 1990s The ISO was the primary architect of the model that is in place today

Characteristics of the OSI Layers

Figure 1-2 demonstrates how the layers are spanned by a routing protocol You might also want to contact Network Associates, as its protocol chart shows how almost every protocol spans the seven layers of the OSI reference model Figure 1-2 provides a good illustration

of how the seven layers are grouped in the model For a better picture of how protocols are positioned in the OSI reference model, visit to the following websites and request a copy

of the applicable posters:

Acterna (aka W&G) offers free OSI, ATM, ISDN, and fiberoptics posters at www.acterna.com/shared/forms/poster_form.html

Network Associates offers its Guide to Communications Protocols at www.sniffer.com/dm/protocolposter.asp

Figure 1-2 How a Routing Protocol Spans the OSI Model

Application Layer

* Provides protocols

to end-user applications

*Provides standardized services to applications

Internet Management

7

Presentation Layer

*Translates the sender's data

to the format of the receiver

*Provides data compression and encryption 6

Session Layer

*Establishes and terminates communication sessions between host processes

*Provides synchronization between address and name databases 5

Network Layer

*Addresses, switches, and routes packets 3

Logical Link Layer

*Provides packet framing

*Controls the physical layer flow of data by mapping between the layers 2

Physical Layer

*Defines electrical and mechanical characteristics such as connectors, pinouts, voltage and current levels

*Provides the interface network devices 1

Network News Transfer Protocol (NNTP) File Transfer Protocol (FTP) Telnet Transfer ProtocolSimple Mail

(SMTP)

TACAS+

Access Control Protocol

TACAS Access Control Protocol

HTTP WWW Hyper Text Transfer Protocol Cisco Gateway Discovery Protocol (GDP)

Network News Transfer Protocol (NNTP)

Exchange Data Representative Light Weight

Protocol (LPP)

Generic Routing Encapsulation (GRE)

Serial Line over IP (SLIP) Compressed Slip (CSLIP)

Cisco Discovery Protocol (CDP)

Internet Control Message Protocol (ICMP)

Packet Level Protocol X.25

Point-to-Point Tunneling (PPTP)

Resource Reservation Protocol (RSVP) RTP Control Protocol (RTPCP) Real-Time Transport Protocol (RTP)

Address Resolution Protocol (ARP)

BPDU Bridge Spanning Tree Protocol

Sub Network Access Protocol (SNAP)

Type 1 Connectionless Service Type 2 Connectionless Service Type 3 Connectionless Service

SMT FDDI Station Management

UTP 4/16 Unshielded Twisted Pair

Shielded Twisted Pair 4/16 Mbps Fiber Optic

Reverse ARP (RARP)

Exterior Gateway Protocol (EGP)

Hot Standby Protocol (HSRP)

Border Gateway Protocol (BGP) Gateway to Gateway Protocol (GGP) Cisco Enhanced IGRP (E-IGRP) Interior Gateway (IGRP) Open Shortest Path First (OSPF)

Next Hop Routing Protocol (NHRP)

CMOT CMIP over TCP

X Windows Hewlett Packard Services DECNet NSP

Simple Network Management Protocol (SNMPv1)

Simple Network Management Protocol (SNMPv2)

Remote UNIX

Routing Protocols

Remote UNIX Print (RPRINT) Remote UNIX Login (RLOGIN)

Remote UNIX Shell (RSHELL)

Game Protocols

Remote UNIX Exec (REXEC)

Remote UNIX WHO Protocol (RWHO)

QUAKE Etc

Bootstrap Protocol (BOOTP)

Gopher

SUN Network Services

Dynamic Host Configuration Protocol (DHCP) DOOM

Trivial File Transfer Protocol (TFTP) Network Time Protocol (NTP)

Domain Name

To NetBIOS

To IPX

To TP

ISO-To DLSW SSP

Radius Remote Authentication Dial-In User Service

User Datagram Transport Control

Protocol (TCP)

Internet Protocol (IP)

802.2 Logical Link Control

Ethernet

LLC 802.2 Ethernet V.2 Internetwork

ISO-DE ISO Deployment Environment

Routing Information Protocol (RIP)

IP Provides links to: PPP, CSLIP, SLIP, XTP, VFRP,

TP, ND, X.25

IEEE 802.4 Token Passing Bus Media Access Control IEEE 802.3 CSMA/CD Media Access Control

IEEE 802.5 Token Passing Ring Media Access Control

IEEE 802.6 Metropolitan Area Network DQDB Media Access Control FDDI Token

Passing Ring Media Access Control ANSI Ethernet Data Link

Control

CDDI Copper Twisted Pair

FDDI Fiber Optic 100 Mbps

SDDI Shielded Copper Ethernet 50 Ohm Coax

100 AnyLAN

VG-100 BASET

100 BASEF

Subscriber Network Interface (SNI)

SONET

DS3 PLCP-T3 -45 Mbps

DS1 PLCP-T1 -1.544 Mbps

DSO

PLCP-64 Kbps

Carrierband Phase Continuous Carrierband Phase Coherent Broadband Multilevel Duobinary

1BASES

10 BROAD 36 Ethernet 50 Ohm Coax Thin Wire 50 Ohm Coax Broadband 75 Ohm Coax

10 Base-T Twisted Pair

10 BASES Thick

10 BASE2 Thin

10 Base-F (A or P) Fiber

CMOT

Remote Procedure Call (RPC)

Table 1-1 outlines an effective mnemonic tool to help you remember the seven OSI layers and their order, working either from Layer 7 down or from Layer 1 up.

Understanding the Seven Layers of the OSI Reference Model

The seven layers of the OSI reference model can be divided into two categories: upper layers and lower layers The upper layers are typically concerned only with applications, and the lower layers primarily handle data transportation The sections that follow examine the three upper layers, the four lower layers, and the functions of each

NOTE The term upper layer is often used to refer to any higher layer, relative to a given layer The

opposite, lower layer, is used to refer to any layer below the one being discussed.

Layer 7—Application

The application layer essentially acts as the end-user interface This is the layer where action between the mail application (cc:Mail, MS Outlook, and so on) or communications package (Secure CRT for Telnet or FTP Voyager for FTP) and the user occurs For example,

OSI Layer (Upper to Lower) Mnemonic OSI Layer (Lower to Upper) Mnemonic

when a user wants to send an e-mail message or access a file on the server, this is where the process starts Another example of the processes that occur at this layer are network file system (NFS) use and the mapping of drives through Windows NT.

Layer 6—Presentation

The presentation layer is responsible for the agreement and translation of the cation format (syntax) between applications For example, the presentation layer enables Microsoft Exchange to correctly interpret a message from Lotus Notes A historical example of why the presentation layer is needed is when a sender is transmitting in EBCDIC (8-bit) character representation to a receiver that needs ASCII (7-bit) character representation Another example of the actions that occur in this layer is the encryption and decryption of data in Pretty Good Privacy (PGP)

Layer 4—Transport

The transport layer is responsible for the logical transport mechanism, which includes functions conforming to the mechanism’s characteristics For example, the transmission control protocol (TCP), a logical transport mechanism, provides a level of error checking and reliability (through sequence numbers) to the transmission of user data to the lower layers of the OSI reference model This is the only layer that provides true source-to-desti-nation, end-to-end connectivity through the use of routing protocols such as open shortest path first (OSPF) or the file transfer protocol (FTP) application as examples of TCP.Contrast the presence of TCP with the user datagram protocol (UDP), which is an unreliable protocol that does not have the additional overhead that provides error checking and reliability like TCP Some common examples of UDP-based protocols are Trivial File Transfer Protocol (TFTP) and Simple Network Management Protocol (SNMP) The most common usage of UDP is streaming media solutions, such as Real Audio

Layer 3—Network

The network layer determines a logical interface address Routing decisions are made based

on the locations of the Internet protocol (IP) address in question For example, IP addresses

establish separate logical topologies, known as subnets Applying this definition to a LAN

workstation environment, the workstation determines the location of a particular IP address and where its associated subnet resides through the network layer For example, there might

be subnet 10.10.10.x, where the customer service people have their workstations or servers, and another subnet 10.20.20.x, where the finance people have their servers or workstations

IP addressing is discussed in more detail later in the section “Internet Protocol Addressing.” Until then, remember that a logical IP address can have three components: network, subnet, and host

Layer 2—Data Link

The data link layer provides framing, error, and flow control across the network media being used An important characteristic of this layer is that the information that is applied

to it is used by devices to determine if the packet needs to be acted upon by this layer (that

is, proceed to Layer 3 or discard) The data link layer also assigns a media access control (MAC) address to every LAN interface on a device For example, on an Ethernet LAN segment, all packets are broadcast and received by every device on the segment Only the device whose MAC address is contained within this layer’s frame acts upon the packet; all others do not

It is important to note at this point that serial interfaces do not normally require unique Layer 2 station addresses, such as MAC addresses, unless it is necessary to identify the receiving end in a multipoint network On networks that do not conform to the IEEE 802 standards but do conform to the OSI reference model, the node address is called the data link control (DLC) address For example, in Frame Relay, this Layer 2 address is known as the data-link connection identifier (DLCI)

MAC addresses are 6 bytes or 48 bits in size, of which 24 bits are dedicated for zation Unique Identification (OUI) and 24 bits are for unique identification See the Institute of Electrical and Electronic Engineers (IEEE) website for more information.The IEEE assigns Ethernet address blocks to manufacturers of Ethernet network interface cards The first 3 bytes of an Ethernet address are the company ID, and the last 3 bytes are assigned by the manufacturer Table 1-2 shows an example of an Ethernet address that is assigned to Cisco Systems

Organi-When discussing MAC addresses, some people refer to the Organization Unique IDs as the vendor ID or OID All are correct; however, the IEEE uses the term shown in Table 1-2.

Layer 1—Physical

The physical layer, the lowest layer of the OSI reference model, is closest to the physical network medium (for example, the network cabling that connects various pieces of network equipment) This layer is responsible for defining information regarding the physical media, such as electrical, mechanical, and functional specifications to connect two systems The physical layer is composed of three main areas: wires, connectors, and encoding Figure 1-3 shows the relationship among the seven layers

Organization Unique ID Assigned by Cisco

Packet

Frame

Bit 1

Communication subnet boundary

Transport

Internal Subnet Protocol

Session Presentation Application

OSI Reference Model Layers and Information Exchange

The seven OSI layers use various forms of control information to communicate with their peer layers in other computer systems This control information consists of specific requests and instructions that are exchanged between peer OSI layers Control information typically takes one of two forms:

• Headers—Appended to the front of data passed down from upper layers

• Trailers—Appended to the back of data passed down from upper layers

OSI layers are not necessarily required to attach a header or trailer to upper-layer data, but they typically do

Headers, Trailers, and Data

Headers (and trailers) and data are relative concepts, depending on the layer that is analyzing the information unit at the time

For example, at the network layer, an information unit consists of a Layer 3 header and data,

known as the payload At the data link layer (Layer 2), however, all the information passed

down by the network layer (the Layer 3 header and the data) is treated simply as data In other words, the data portion of an information unit at a given OSI layer can potentially contain headers,

trailers, and data from all the higher layers This is known as encapsulation Figure 1-4 shows

the header and data from one layer that are encapsulated in the header of the next-lowest layer

This discussion described the framework that is used to tie networks together There are now hundreds of online and print references that spend even more time discussing the OSI model, but for this text, the level of discussion presented here is appropriate However, note that how networks communicate has not been discussed The following section reviews the basic principles of TCP/IP—the de facto standard for communication on the Internet

Host A

Data Header 4 Data Header 3

Data Header 2

Data Network

Host B

Information Units

.

Application Presentation Session Transport Network Data Link Physical

Application Presentation Session Transport Network Data Link Physical

TCP/IP Protocol Suite

A protocol is a set of rules and conventions that govern how devices on a network exchange

information This section discusses one of the more commonly used protocol suites: TCP/IP This discussion does not provide sufficient information for an in-depth study of TCP/IP Nevertheless, TCP/IP needs to be covered to some degree so that you can better understand the overall operation of network protocols; these discussions are expanded in later chapters concerning OSPF

The TCP/IP protocol suite is also referred to as the TCP/IP stack, and it is one of the most widely implemented internetworking standards in use today The term TCP/IP literally

means Transmission Control Protocol/Internet Protocol TCP and IP are the two core

protocols that exist within the TCP/IP protocol suite, and their place in the TCP/IP protocol stack is clarified in the following paragraphs

TCP/IP was originally developed for ARPAnet, a U.S Government packet-switched WAN, over 25 years ago Although at the time, the Internet was a private network and TCP/IP was designed specifically for use within that network, TCP/IP has since grown in popularity and

is one of the most open protocols available for use in networks today This growth and popularity is primarily due to TCP/IP’s capability to connect different networks regardless

of their physical environments This has made TCP/IP today’s de facto standard on the Internet and in the majority of today’s networks, large and small

TCP/IP is not 100 percent compatible with the OSI reference model; however, TCP/IP can run over OSI-compliant lower layers, such as the data link and physical layers of the OSI model TCP/IP can communicate at the network layer as well using IP Essentially, layers 3 and below

in the OSI reference model are close to the original TCP/IP structure Figure 1-5 illustrates this mapping of layers between the OSI model and the TCP/IP protocol

Application Presentation Session Transport Network Data Link Physical

7 6 5 4 3 2 1

OSI Model

Application

Transport Network Data Link Physical

TCP/IP Model

5 4 3 2 1 TCP/UDP

IP

TCP/IP Functions

Whereas OSI was a structure for networks, you can consider TCP/IP the language of the networks When combined, networks create a diverse and powerful network—the Internet This section reviews the major functionality of TCP/IP in general and then TCP and IP in turn

The term segment describes a unit of data at the TCP layer At the IP layer, it is called a

packet, and at the lower layers, it is called a frame The various names are shown in Figure 1-3.

If a message is too large for the underlying network topology, it is up to the IP layer to fragment the datagram into smaller parts For example, Ethernet frame sizes differ from what is allowable in Token Ring; therefore, IP handles the size changes as needed.Different paths might be available through the Internet, between a source and a destination station Fragments of a datagram might take different paths through a network So, when messages arrive at the destination station, the IP protocol stack must sequence them and reassemble them into their original datagram Each datagram or fragment is given an IP header and is transmitted as a frame by the lower layers

NOTE In addition to the two network layer protocols (IP and Internet control message protocol

[ICMP]) and the two transport layer protocols (TCP and UDP), the TCP/IP suite includes

a cluster of protocols that operates at the upper layers, such as FTP, Telnet, and so on.Some of these are TCP/IP-specific, and some are protocols that can run with TCP/IP but originate elsewhere; however, discussion of these advanced protocols is beyond the scope

of this book

A good resource for further reading on the subject of TCP/IP is TCP/IP Illustrated, Volume 1,

by Richard Stevens It is somewhat dated in its examples, but the text is definitive Also, by the time you read this, Stevens’s second edition should be published Hopefully, the high standards of the original volume will be maintained because Mr Stevens has regretfully passed away and did not revise the first edition

TCP Overview

Within this suite of protocols, TCP is the main transport layer protocol that offers connection-oriented transport services TCP accepts messages from upper-layer protocols and provides the messages with an acknowledged reliable connection-oriented transport service to the TCP layer of a remote device TCP provides five important functions within the TCP/IP protocol suite:

• Provides format of the data and acknowledgments that two computers exchange to achieve a reliable transfer

• Ensures that data arrive correctly

• Distinguishes between multiple destinations on a given machine

• Explains how to recover from errors

• Explains how a data stream transfer is initiated and when it is complete

IP Overview

IP is the main network-layer protocol It offers unreliable, connectionless service because

it depends on TCP to detect and recover from lost packets when TCP is being used natively, when UDP is used, there is no recovery of lost packets because UDP does not have that capability IP provides three important functions within the TCP/IP protocol suite:

Alter-• Defines the basic format and specifications of all data transfer used throughout the protocol suite

• Performs the routing function by choosing a path to the required destination over which data is to be sent

• Includes the previously mentioned functions as well as those covering unreliable packet delivery

Essentially, these functions cover how packets should be processed, what error message parameters are, and when a packet should be discarded

Types of Network Topologies

The preceding sections discussed the evolution of today’s advanced networks and the building blocks that have evolved to make them what they are today—that is, the OSI reference model and the TCP/IP protocol The sections on the OSI reference model described the essential means of how data is transported between the various layers that are running on all intranet devices The TCP/IP section reviewed the protocols’ characteristics This section addresses the media that operates in your network The sections that follow review both LAN and WAN topologies

Local-Area Networks

LANs connect workstations, servers, legacy systems, and miscellaneous sible equipment, which are, in turn, interconnected to form your network The most common types of LANs are as follows:

network-acces-• Ethernet—A communication system that has only one wire with multiple stations

attached to the single wire; the system operates at a speed of 10 Mbps Ethernet is currently traditionally found based on copper wire You can contrast this with Fast Ethernet and Gigabit Ethernet, which have been developed on both copper wire and fiberoptic cabling

• Fast Ethernet—An improved version of Ethernet that also operates with a single wire

with multiple stations However, the major improvement is in the area of speed; Fast Ethernet operates at a speed of 100 Mbps

• Gigabit Ethernet—Yet another version of Ethernet that allows for operational speeds

of 1 Gbps The functional differences between copper- and fiber-based Gigabit Ethernet can affect design and operation

• Token Ring—One of the oldest “ring” access techniques that was originally proposed

in 1969 It has multiple wires that connect stations by forming a ring and operates at speeds of 4 Mbps and 16 Mbps Token Ring is mentioned here as a courtesy to IBM (its creator); it is rarely used today

• Fiber distributed data internetworking (FDDI)—A dual fiberoptic ring that

provides increased redundancy and reliability FDDI operates at speeds of 100 Mbps FDDI is still in use, but Gigabit Ethernet and Synchronous Optical Network (SONET), mentioned in the next section, might make FDDI obsolete

Figure 1-6 shows a typical Ethernet LAN

For further information on this subject, visit the following website:

• Frame Relay—A good, connection-oriented, frame-switched protocol for connecting

sites over a WAN Frame Relay is a great solution for enterprise networks that require

a multipoint WAN media

Backbone cable

Node

• Leased lines—A dedicated connection from two distinct points that commonly uses

the point-to-point protocol to provide various standards through encapsulation for IP traffic between serial links

• Asynchronous transfer mode (ATM)—ATM is an International Telecommunications

Union–Telecommunication Standardization Sector (ITU-T) standard for cell relay Information is conveyed in small, fixed-size cells ATM is a high-speed, low-delay multiplexing and switching technology that can support any type of user traffic, including voice, data, and video applications that are defined by the American National Standards Institute (ANSI) and International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) standards committees for the transport of a broad range of user information ATM is ideally suited to applications that cannot tolerate time delay, as well as for transporting IP traffic

• Integrated Systems Digital Network (ISDN)—Consists of digital telephony and

data transport services using digitization over a specialized telephone network The future of ISDN is in question because of the development of digital subscriber line and cable modem technologies

• Digital subscriber line (DSL)—An always-on Internet connection that is typically

billed monthly, usually for a fixed price and unlimited usage DSL, when installed as

a wall socket, looks much like a phone socket In the United States, the wall socket is,

in fact, a phone socket and, for the popular residential type of DSL (asymmetric digital subscriber line [ADSL]), the phone wiring does indeed carry phone and data signals The key advantage of DSL over dial-up modems is its speed DSL is from several

to dozens of times faster than a dial-up modem connection DSL is also a great way to save money compared to pay-per-minute ISDN data lines or expensive T1 lines

• Cable modem—Refers to a modem that operates over the ordinary cable TV network

cables Because the coaxial cable used by cable TV provides much greater bandwidth than telephone lines, a cable modem can be used to achieve extremely fast access to the World Wide Web The term “Cable Modem” is a bit misleading, as a Cable Modem works more like a LAN interface than as a modem Basically, you just connect the Cable Modem to the TV outlet for your cable TV, and the cable TV operator connects

a Cable Modem Termination System (CMTS) in his end (the Head-End)

• SONET—An optical fiber-based network created by Bellcore in the mid-1980s It is

now an ANSI standard The international equivalent of SONET is synchronous digital hierarchy (SDH) SONET defines interface standards at the physical layer of the OSI seven-layer model The SONET ANSI standard defines a hierarchy of interface rates that allow data streams of different rates to be multiplexed from optical carrier (OC) levels, from 51.8 Mbps (about the same as a T-3 line) to 2.48 Gbps The international equivalent of SONET, standardized by the ITU, is called SDH SONET is considered

to be the foundation for the physical layer of broadband ISDN (BISDN) Asynchronous transfer mode runs can also run on top of SONET as well as on top of other technologies

• Dense wave division multiplexing (DWDM)—An optical multiplexing technique

that is used to increase the carrying capacity of a fiber network beyond what can currently be accomplished by time-division multiplexing (TDM) techniques DWDM replaces TDM as the most effective optical transmission method Different wavelengths

of light are used to transmit multiple streams of information along a single fiber with minimal interference Using DWDM, up to 80 (and theoretically more) separate wavelengths or channels of data can be multiplexed into a light stream that is transmitted on a single optical fiber DWDM is also sometimes called wave division multiplexing (WDM) Because each wavelength or channel is demultiplexed at the end of the transmission back into the original source, different data formats being transmitted at different data rates can be transmitted together DWDM will allow SONET data and ATM data to be transmitted at the same time within the optical fiber

These WAN technologies are only briefly covered in this book However, their connectivity and protocol characteristics are compared Figure 1-7 shows some of the basic differences and choices that are considered when switching is involved

Table 1-3 summarizes the various carrier speeds and characteristics This information is a good reference going forward and as the industry develops higher speeds

WAN Options

Leased Lines:

Fractional T1/E1 T1/E1 T3/E3

Circuit Switched Packet/CellSwitched

Basic Telephone Service ISDN Switched 56

X.25 Frame Relay (PVCs & SVCs) ATM SMDS Cable Modems

DSL

*STS-1 is electrical equivalent of OC-1 E0 = 64 kbps

STS-1 = OC1 = 51.84 Mbps (base rate) 4 * E1 = E2

STS-3 = OC3 = STM-1 = 155 Mbps 4 * E2 = E3

STS-9 = OC9 = STM-3 = 9 times base rate (not used) E3 = 34 Mbps in or around

STS-12 = OC12 = STM-4 = 622 Mbps STM = synchronous transport module (ITU–T) STS-18 = OC18 = STM-6 = 18 times base rate (not used) STS = synchronous transfer signal (ANSI)

STS-24 = OC24 = STM-8 = 24 times base rate (not used) OC = optical carrier (ANSI)

STS-36 = 0C36 = STM-12 = 36 times base rate (not used) Although an SDH STM–1 has the same bit rate as the STS-48 = OC48 = STM-16 = 2.5 Gbps SONET STS–3, the two signals contain different frame E1 = 32 64-kbps channels = 2.048 Mbps structures.

Digital Signal

(DS) Name

Circuit Bit Rate

Number of DS0s Used

Equivalent T-Carrier Name

Equivalent E-Carrier Name

SONET Signal Bit Rate SDH Signal SONET Capacity SDH Capacity