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 3—Network 11 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 VLSMs 35

VLSM Design Guidelines and Techniques 36 CIDR 37

Validating a CIDRized Network 37 What Do Those Slashes Mean? 38 Important CIDR Terms 38 IP Classless 39 CIDR Translation Table 39

Manually Computing the Value of a CIDR IP Prefix 40 Case Study: VLSMs 41

Route Aggregation 42 Summary 44

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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 VLSM and CIDR Support 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 Summary 101

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 4: ASBR Summary LSAs 108 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 Summary 158

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

OSPF Network Design Methodology 167 Step 1: Analyze the Requirements 168 OSPF Deployment 169 Load Balancing with OSPF 170 OSPF Convergence 170 Step 2: Develop the Network Topology 171 Fully Meshed Topology 171 Hierarchical Topology 171

OSPF Backbone Design in the Hierarchical Model 173 Area Design in the Hierarchical Model 174 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 Naming Schemes 186 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

Configuring a Neighbor's Cost on Point-to-Multipoint Broadcast Networks 231 Configuring an Interface as Point-to-Multipoint Nonbroadcast 231 Configuring Route Calculation Timers 232 Suppressing OSPF Updates 232 Summary 232 Case Studies 233

Case Study: Understanding Subinterfaces 233 Point-to-Point Subinterfaces 233 Multipoint Subinterfaces 234 Case Study: Point-to-Multipoint Link Networks 235 Router Configuration Examples 237 Case Study Conclusion 239 Case Study: Designing an OSPF Network 240 New WAN Requirements 242

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

network Command 272 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 Summary 328

Case Study: Assigning Unique Network Numbers to Each OSPF Area 329

Case Study: OSPF with Multiple Areas 330

Case Study: OSPF with Stub and Totally Stubby Areas 335

Chapter 6 Redistribution 339

OSPF Redistribution 340

Administrative Distance and Metrics 341 Redistribution Golden Rules 342 Redistribution Configuration 343 External Routes 347 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 Route Maps 365

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 4G6 Benefits of Summarization 4GS Summarization Golden Rules 4G9 Troubleshooting Summarization 41G Types of OSPF Summarization 41G Summarize Area Routes 411 Summarize External Routes 414 Summarizations Effect on the Routing Table 41S Configuration Example 3: Subnetting with Summarization 42G Alternative Area Summarization Example 423 Using Private Addressing to Summarize? 424 Configuration Example 4: Using VLSM with Summarization 426 Summary 431

Final Router Example Configurations 431 Part III OSPF Implementation, Troubleshooting, and Management 439

Chapter 8 Managing and Securing OSPF Networks 441

Network Management 442

Network Management Tools 444 CiscoView 444 CiscoWorks 445 Cisco ConfigMaker 446 Simple Network Management Protocol 446 Introduction to SNMP 45G

Network Management System 451 Agents 452 Managed Devices 452 Management Information Base Overview 453 SNMP Operation 455

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 OSPF MIBs 462 Network Security 466

Assessing the Need for Security 467 Golden Rules for Designing a Secure Network 467 Document Your Security Plan 468 Know Your Enemy 469 Count the Cost 469 Identify Your Assumptions 47G Control and Limit Your Secrets 47G 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 Summary 505

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 Configuring 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

show ip ospf maxage-list Command (Hidden) 579 show ip ospf neighbor Command 580 show ip ospf neighbor ip address Command 581 show ip ospf neighbor int ip-address Command 581 show ip ospf neighbor detail Command 581 show ip ospf virtual-links Command 583 show ip ospf stat Command (Hidden) 583 show ip ospf summary-address Command 585 clear ip ospf Command 585

clear ip ospf counters Command 585 clear ip ospf process Command 586 clear ip ospf redistribution Command 587 OSPF debug Commands 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 Summary 615

Case Study: In the Trenches with OSPF 616 Problem No. 1 616

Step 1: Define the Problem 617 Step 2: Gather Facts 617 Step 3: Consider Possible Problems 621 Step 4: Create an Action Plan 622 Step 5: Implement the Action Plan 622 Step 6: Gather Results 623

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 Stuck in EXSTART/EXCHANGE 638 OSPF Stuck in LOADING 641 OSPF Stuck in TWO-WAY 641 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 MPLS and OSPF 683

Background of MPLS 684 What Is the Benefit of MPLS? 686 Why Not IP Routing or ATM Switching? 686 Conventional Best Effort Routing 687 MPLS Overview 689 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 Summary 703

Part IV Additional OSPF Resources 705

Appendix A Overview of the OSPF RFCs 707

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