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Ospf Network Design Solutions 2nd Edition 2nd Edition Tom Thomas

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Ospf Network Design Solutions 2nd Edition 2nd Edition Tom Thomas Ospf Network Design Solutions 2nd Edition 2nd Edition Tom Thomas Ospf Network Design Solutions 2nd Edition 2nd Edition Tom Thomas

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Ospf Network Design Solutions 2nd Edition 2nd Edition Tom Thomas
Cisco Press 201 West 103rd Street Indianapolis, IN 46290 USA Cisco Press OSPF Network Design Solutions Second Edition Thomas M.Thomas II, CCIE No. 9360 0323FMf.book Page i Wednesday, March 12, 2003 9:41 AM
ii OSPF Network Design Solutions, Second Edition Thomas M. Thomas II Copyright© 2003 Cisco Systems, Inc. Published by: Cisco Press 201 West 103rd Street Indianapolis, IN 46290 USA All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the publisher, except for the inclusion of brief quotations in a review. Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 First Printing April 2003 Library of Congress Cataloging-in-Publication Number: 2001095162 ISBN: 1-58705-032-3 Warning and Disclaimer This book is designed to provide information about the Open Shortest Path First (OSPF) protocol. Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied. The information is provided on an “as is” basis. The authors, Cisco Press, and Cisco Systems, Inc. shall have neither liability nor responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book or from the use of the discs or programs that may accompany it. The opinions expressed in this book belong to the author and are not necessarily those of Cisco Systems, Inc. Trademark Acknowledgments All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Cisco Press or Cisco Systems, Inc. cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. Feedback Information At Cisco Press, our goal is to create in-depth technical books of the highest quality and value. Each book is crafted with care and precision, undergoing rigorous development that involves the unique expertise of members from the professional technical community. Readers’ feedback is a natural continuation of this process. If you have any comments regarding how we could improve the quality of this book, or otherwise alter it to better suit your needs, you can contact us through email at feedback@ciscopress.com. Please make sure to include the book title and ISBN in your message. We greatly appreciate your assistance. 0323FMf.book Page ii Wednesday, March 12, 2003 9:41 AM
iii Publisher John Wait Editor-In-Chief John Kane Cisco Representative Anthony Wolfenden Cisco Press Program Manager Sonia Torres Chavez Manager, Marketing Communications, Cisco Systems Scott Miller Cisco Marketing Program Manager Edie Quiroz Executive Editor Brett Bartow Acquisitions Editor Amy Moss Production Manager Patrick Kanouse Development Editor Christopher Cleveland Project Editor San Dee Phillips Copy Editor Progressive Publishing Alternatives Technical Editors Henry Benjamin, Matthew Birkner, Rick Burts, Daniel Golding, John Hammond, Cary Riddock Team Coordinator Tammi Ross Book Designer Gina Rexrode Cover Designer Louisa Adair Indexer Tim Wright 0323FMf.book Page iii Wednesday, March 12, 2003 9:41 AM
iv 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 Communica- tion and Services). Formerly with the Cisco Systems CCIE global team, Henry is now an independent consultant for a large security firm in Australia. He has served as a proctor for the CCIE Lab exams and is the 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. 0323FMf.book Page iv Wednesday, March 12, 2003 9:41 AM
v 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 to keep me going. I want to reaffirm a few words of special meaning to my wife and I who have been married for over 15 years… Always Forever Endlessly Until Eternity Acknowledgments I am very grateful to the group of talented people that were assembled to make this book a reality. Through their knowledge, dedication, and hard work, this book has become more than I ever thought possible. The most important acknowledgment must go to my wife, Rose, who put up with me writing all night after working all day. Her unwavering support was the single greatest factor in my ability to complete the book you now hold in your hands. 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. 0323FMf.book Page v Wednesday, March 12, 2003 9:41 AM
vi 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 Index 724 0323FMf.book Page vi Wednesday, March 12, 2003 9:41 AM
vii 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 0323FMf.book Page vii Wednesday, March 12, 2003 9:41 AM
viii 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 0323FMf.book Page viii Wednesday, March 12, 2003 9:41 AM
ix 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 0323FMf.book Page ix Wednesday, March 12, 2003 9:41 AM
x 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 0323FMf.book Page x Wednesday, March 12, 2003 9:41 AM
xi 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 0323FMf.book Page xi Wednesday, March 12, 2003 9:41 AM
xii 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 0323FMf.book Page xii Wednesday, March 12, 2003 9:41 AM
xiii 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 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 450 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 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 0323FMf.book Page xiii Wednesday, March 12, 2003 9:41 AM
xiv 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 0323FMf.book Page xiv Wednesday, March 12, 2003 9:41 AM
xv 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 0323FMf.book Page xv Wednesday, March 12, 2003 9:41 AM
xvi 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 0323FMf.book Page xvi Wednesday, March 12, 2003 9:41 AM
xvii 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 Router Bridge Hub DSU/CSU Catalyst Switch Multilayer Switch ATM Switch ISDN/Frame Relay Switch Communication Server Gateway Access Server PC PC with Software Sun Workstation Macintosh Terminal File Server Web Server Cisco Works Workstation Printer Laptop IBM Mainframe Front End Processor Cluster Controller 0323FMf.book Page xvii Wednesday, March 12, 2003 9:41 AM
xviii 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. • Boldface indicates 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 0323FMf.book Page xviii Wednesday, March 12, 2003 9:41 AM
xix Introduction OSPF is in use in numerous networks worldwide. OSPF is also one of the most widely tested on proto- 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 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-StateAdvertisement (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. 0323FMf.book Page xix Wednesday, March 12, 2003 9:41 AM
xx • 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. 0323FMf.book Page xx Wednesday, March 12, 2003 9:41 AM
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I P A R T OSPF Fundamentals and Communication Chapter 1 Networking and Routing Fundamentals Chapter 2 Introduction to OSPF Chapter 3 OSPF Communication 0323FMf.book Page 3 Wednesday, March 12, 2003 9:41 AM
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C H A P T E R 1 Networking and Routing Fundamentals Achievement: Unless you try to do something beyond what you have already mastered, you will never grow.—Successories In recent years, the growth of networks everywhere has accelerated as many organizations move into the international business arena and join the Internet community. This expansion continues to drive the development, refinement, and complexity of network equipment and software, consequently resulting in some unique issues and exciting advances. You rarely see an advertisement that does not contain the famous www prefix. In my hometown, one 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. 0323FMf.book Page 5 Wednesday, March 12, 2003 9:41 AM
6 Chapter 1: Networking and Routing Fundamentals Figure 1-1 Moore’s Law Foundations of Networking Many advanced features are being supported by the physical hardware through the appli- cation of Moore’s law. Those of us responsible for networking these many devices follow a theoretical framework that allows the required functionality to be deployed within our networks. This framework is more commonly known as the OSI reference model. 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. 100,000 10,000 1000 100 10 1 4004 8086 80,286 80,386 80,486 Intel CPUs 2.5 years Thousands of Transistors Year: 1975 1980 1985 1990 1995 2000 Doubling time of fitted line is 2.0 years. P5 (Pentium) P6 (Pentium Pro) P7 (Merced) 0323FMf.book Page 6 Wednesday, March 12, 2003 9:41 AM
Foundations of Networking 7 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. 0323FMf.book Page 7 Wednesday, March 12, 2003 9:41 AM
8 Chapter 1: Networking and Routing Fundamentals 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 Transport Layer *Provides error free and reliable packet delivery *Fragments and reassembles packets while managing network layer connections 4 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 Simple Mail Transfer Protocol (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 Protocol (XDR) Light Weight Presentation 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 Routing Protocol (IGRP) Open Shortest Path First (OSPF) Next Hop Routing Protocol (NHRP) CMOT CMIP over TCP X Windows Hewlett Packard Network 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 System (DNS) To NetBIOS To IPX To ISO- TP To DLSW SSP Radius Remote Authentication Dial-In User Service User Datagram Protocol (UDP) Transport Control Protocol (TCP) Internet Protocol (IP) 802.2 Logical Link Control Ethernet Ethernet V.2 Token Bus Token Ring FDDI 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, RTP, RSVP, RTCP, CLNP, ISO 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 VG- AnyLAN 100 BASET 100 BASEF 1 BASE5 G. 703 PLCP 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 StarLAN 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) 0323FMf.book Page 8 Wednesday, March 12, 2003 9:41 AM
Understanding the Seven Layers of the OSI Reference Model 9 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. Upper Layers The upper layers of the OSI reference model—5, 6, and 7—are concerned with application issues. They are generally implemented only in software programs. The application layer is the highest layer and is closest to the end user. Both users and application layer processes interact with software programs that contain a communications component so that the application can interact with the OSI model effectively. The sections that follow review the functions of each upper layer in detail. 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 inter- action between the mail application (cc:Mail, MS Outlook, and so on) or communications package (Secure CRT for Telnet or FTPVoyager for FTP) and the user occurs. For example, Table 1-1 Mnemonics Used to Remember OSI Layers OSI Layer (Upper to Lower) Mnemonic OSI Layer (Lower to Upper) Mnemonic Application (Layer 7) All Physical (Layer 1) Please Presentation (Layer 6) people Data Link (Layer 2) do Session (Layer 5) seem Network (Layer 3) not Transport (Layer 4) to Transport (Layer 4) take Network (Layer 3) need Session (Layer 5) sales Data Link (Layer 2) data Presentation (Layer 6) peoples Physical (Layer 1) processing Application (Layer 7) advice 0323FMf.book Page 9 Wednesday, March 12, 2003 9:41 AM
10 Chapter 1: Networking and Routing Fundamentals 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 communi- 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 5—Session The session layer responsibilities range from managing the application layer’s transfer of information to the data transport portion of the OSI reference model. An example is Sun’s or Novell’s Remote Procedure Call (RPC), which uses Layer 5. Lower Layers The lower layers of the OSI reference model—1, 2, 3, and 4—handle data transport issues. The physical and data link layers are implemented in hardware and software. The other lower layers are generally implemented only in software. These lower layers are the ones that network engineers and designers need to focus on to be successful. The sections that follow review the functions of each of the lower layers in detail. 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. 0323FMf.book Page 10 Wednesday, March 12, 2003 9:41 AM
Understanding the Seven Layers of the OSI Reference Model 11 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 ProtocolAddressing.” 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 Organi- 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. 0323FMf.book Page 11 Wednesday, March 12, 2003 9:41 AM
12 Chapter 1: Networking and Routing Fundamentals 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. Figure 1-3 Detailed OSI Layer Relationships Table 1-2 Example Ethernet Address Organization Unique ID Assigned by Cisco 00 00 0C 01 23 45 Application 7 OSI Layer Name of Unit Exchanged Presentation 6 Session 5 Transport 4 Network 3 Data Link 2 Physical Application Presentation Session Transport Network Data Link Physical Host A Host B APDU PPDU SPDU Segment (TCP) Datagram (UDP) Packet Frame Bit 1 Communication subnet boundary Transport Internal Subnet Protocol Session Presentation Application Router Router Network Data Link Physical Network Data Link Physical Protocol Data Unit 0323FMf.book Page 12 Wednesday, March 12, 2003 9:41 AM
OSI Reference Model Layers and Information Exchange 13 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,thedataportionofaninformationunitatagivenOSIlayercanpotentiallycontainheaders, 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. Figure 1-4 OSI Packet Encapsulation Through the OSI Layers 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 0323FMf.book Page 13 Wednesday, March 12, 2003 9:41 AM
14 Chapter 1: Networking and Routing Fundamentals 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 forARPAnet, 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. Figure 1-5 OSI Model–to–TCP/IP Mappings 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 0323FMf.book Page 14 Wednesday, March 12, 2003 9:41 AM
TCP/IP Protocol Suite 15 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 0323FMf.book Page 15 Wednesday, March 12, 2003 9:41 AM
16 Chapter 1: Networking and Routing Fundamentals • 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. Alter- 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: • 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 network-acces- sible equipment, which are, in turn, interconnected to form your network. The most common types of LANs are as follows: • 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. 0323FMf.book Page 16 Wednesday, March 12, 2003 9:41 AM
Types of Network Topologies 17 • 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. Figure 1-6 Typical Ethernet LAN For further information on this subject, visit the following website: www.ethermanage.com/ethernet/ethernet.html Wide-Area Networks WANs are used to connect physically separated applications, data, and resources, thereby extending the reach of your network to form an intranet. The ideal result is seamless access to remote resources from geographically separated end users. The most common types of WAN connectivity technologies include the following: • 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 0323FMf.book Page 17 Wednesday, March 12, 2003 9:41 AM
18 Chapter 1: Networking and Routing Fundamentals • 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 theWorldWideWeb. 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 anANSI 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. 0323FMf.book Page 18 Wednesday, March 12, 2003 9:41 AM
Types of Network Topologies 19 • 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. Figure 1-7 Available WAN Technology Options 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. WANOptions Dedicated Switched LeasedLines: FractionalT1/E1 T1/E1 T3/E3 Circuit Switched Packet/Cell Switched BasicTelephone Service ISDN Switched56 X.25 FrameRelay (PVCs&SVCs) ATM SMDS CableModems DSL 0323FMf.book Page 19 Wednesday, March 12, 2003 9:41 AM
20 Chapter 1: Networking and Routing Fundamentals *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. Table 1-3 Carrier Rates and Transmission Characteristics* Digital Signal (DS) Name Circuit Bit Rate Number of DS0s Used Equivalent T-Carrier Name Equivalent E-Carrier Name DS0 64 Kbps 1 - - DS1 1.544 Mbps 24 T-1 - - 2.048 Mbps 32 - E-1 DS1C 3.152 Mbps 48 - - DS2 6.312 Mbps 96 T-2 - - 8.448 Mbps 128 - E-2 - 34.368 Mbps 512 - E-3 DS3 44.736 Mbps 672, or 28 DS1s T-3 - - 139.264 Mbps 2048 - E-4 DS4/NA 139.264 Mbps 2176 - - DS4 274.176 Mbps 4032 - - - 565.148 Mbps 4 E-4 Channels - E-5 SONET Signal Bit Rate SDH Signal SONET Capacity SDH Capacity OC–1 (STS-1) 51.84 Mbps STM–0 28 DS–1s or 1 DS–3 21 E1s OC–3 (STS-3) 155.52 Mbps STM–1 84 DS–1s or 3 DS–3s 63 E1s or 1 E4 OC–12 (STS–12) 622.08 Mbps STM–4 336 DS–1s or 12 DS–3s 252 E1s or 4 E4s OC–48 (STS–48) 2.488 Gbps STM–16 1344 DS–1s or 48 DS–3s 1008 E1s or 16 E4s OC–192 (STS–192) 10 Gbps STM–64 5376 DS–1s or 192 DS–3s 4032 E1s or 64 E4s OC-256 13.271 Gbps - - - OC-768 40 Gbps - - - 0323FMf.book Page 20 Wednesday, March 12, 2003 9:41 AM
IP Addressing 21 IP Addressing This section discusses IP addressing methodology, basic subnetting, variable-length subnet masking (VLSM), and classless interdomain routing (CIDR). In a properly designed and configured network, communication between hosts and servers is transparent. This is because each device that uses the TCP/IP protocol suite has a unique 32-bit IP address. A device reads the destination IP address in the packet and makes the appropriate routing decision based on this information. In this case, a device might be either the host or server using a default gateway or a router using its routing table to forward the packet to its destination. Regardless of what the device is, the communication is easily accomplished and transparent to the user as a result of proper IP addressing. IP addresses can be represented as a group of four decimal numbers, each within the range of 0 to 255. Each of these four decimal numbers is separated by a decimal point. The method of displaying these numbers is known as dotted decimal notation. Note that these numbers can also be displayed in both the binary and hexadecimal numbering systems. Figure 1-8 illustrates the basic format of an IP address as determined by using dotted decimal notation. Figure 1-8 IP Address Format as Determined by Dotted Decimal Notation IP addresses have two primary logical components, network and host portions, the difference and use of which is extremely important. A third component, the subnet, is also used. A network address identifies the logical network and must be unique; if the network is to be a part of the Internet, the network must be assigned by American Registry for Internet Numbers (ARIN) in North America, Réseaux IP Européens (RIPE) in Europe, and Asia Pacific Network Information Centre (APNIC) in Asia. A host address, on the other hand, identifies a host (device) on a network and is assigned by a local administrator. ! # 0323FMf.book Page 21 Wednesday, March 12, 2003 9:41 AM
22 Chapter 1: Networking and Routing Fundamentals Consider a network that has been assigned an address of 172.24. An administrator then assigns a host the address of 248.100. The complete address of this host is 172.24.248.100. This address is unique because only one network and one host can have this address. NOTE In many cases when dealing with advanced networking topics such as OSPF, the latest trend is to write IP addresses as follows: x.x.x.x/8 or /16 or /24. This has become an accepted method of shorthand for IP addressing. The number to the right of the slash (/) represents the number of bits in the subnet mask. Class A Addresses In a Class A address (also known as /8), the first octet contains the network address and the other three octets make up the host address. The first bit of a Class A network address must be set to 0. Although mathematically it would appear that there are 128 possible Class A network addresses (the first bit is set to 0), the address 00000000 is not available, so there are only 127 such addresses. This number is further reduced because network 127.0.0.0 is reserved for loopback addressing purposes and 10.0.0.0 is a reserved private range. This means that only 126 ClassA addresses are available for use. However, each ClassA address can support 126 networks that correspond to 16,777,214 node addresses per Class A address. NOTE IP addresses or masks of either all 1s or all 0s in each octet are not usually allowed or used in a classful network implementation. The introduction of CIDR now allows most service providers to assign addresses in /19 or /20. Cisco has made exceptions in using all 1s or all 0s, but for this discussion, consider this practice as being not allowed. Class B Addresses In a Class B (also known as /16) address, the network component uses the first two octets for addressing purposes. The first 2 bits of a Class B address are always 10; that is, 1 and 0, not ten. The address range would then be 128.0.0.0 to 191.255.255.255. This makes available the first 6 bits of the first octet and all 8 bits of the second octet, thereby providing 16,384 possible Class B network addresses. The remaining octets are used to provide over 65,534 hosts per Class B address. 0323FMf.book Page 22 Wednesday, March 12, 2003 9:41 AM
IP Addressing 23 Class C Addresses In a Class C (also known as /24) address, the first three octets are devoted to the network component. The first 3 bits of a Class C address must be 110. The address range would then be 192.0.0.0 to 223.255.255.255. This leaves 5 bits of the first octet and 8 bits of the second and third octets, thereby providing 2,097,152 possible Class C addresses. The node address is determined by the last octet, which provides 254 nodes per network. Class D Addresses Class D addresses are special addresses that do not refer to individual networks. The first 4 bits of these addresses are 1110. The address range would then be in the range of 224 to 239. Class D addresses are used for multicast packets, which are used by many different protocols to reach multiple groups of hosts (such as ICMP router discovery or Internet group membership protocol [IGMP], which is gaining in popularity since its release in Cisco IOS Software Release 11.2). Consider these addresses as being preprogrammed within the logical structure of most network components in that when they see a destination address of this type within a packet, the address triggers a response. For example, if a host sends a packet out to the destination IP address 224.0.0.5, all routers (using OSPF) on this address’s Ethernet segment respond. Class E Addresses Addresses in the range of 240.0.0.0 to 255.255.255.255 are termed Class E addresses. The first octet of these addresses begins with the bits 1111. These addresses are reserved for future additions to the IP addressing scheme. These future additions might or might not come to fruition with the advent of IP version 6 (IPv6). In most networks, the assigned IP addresses have been broken into parts that logically relate to different areas. For example, part of an IP address identifies a particular network, part identifies a subnet (that is, subnetwork), and part identifies a specific host within that subnetwork (that is, a subnet). The following three blocks of IP address space for private networks have been reserved according to RFC 1918, “Address Allocation for Private Internets”: • 10.0.0.0–10.255.255.255—Single Class A network numbers • 172.16.0.0–172.31.255.255—Contiguous Class B network numbers • 192.168.0.0–192.168.255.255—Contiguous Class C network numbers NOTE You can also write these three networks as 10/8, 172.16/12, and 192.168/16, using the slash method to represent the address. 0323FMf.book Page 23 Wednesday, March 12, 2003 9:41 AM
24 Chapter 1: Networking and Routing Fundamentals How IP Addresses Are Used Routers examine the most significant or left-most bit of the first octet when determining the class of a network address. This technique of reading IP addresses (also known as the first octet rule) is discussed further as the different classes of addresses are defined. Table 1-4 provides information regarding the different IP address classes. Note that in the format column, N equals the network number and H equals the host number.Also, for Class A addresses, one address is reserved for the broadcast address and one address is reserved for the network. Tables 1-5 through 1-7 list the number of hosts and subnets for Class A, B, and C IP addresses. For the subnets and hosts, all 0s and 1s are excluded. Table 1-4 IP Address Quick-Reference Information Class Format Purpose High- Order Bit Address Range Network/ Host Bits Maximum Number of Hosts A N.H.H.H Large organizations 0 1.0.0.0– 126.255.255.255 7/24 16,777,214 (224 – 2) B N.N.H.H Medium organizations 10 128.0.0.0– 191.255.255.255 14/16 65,534 (216 – 2) C N.N.N.H Small organizations 110 192.0.0.0– 223.255.255.255 22/8 254 (28– 2) D N/A Multicast 1110 224.0.0.0– 239.255.255.255 N/A N/A E N/A Experimental 11110 240.0.0.0– 254.255.255.255 N/A N/A Table 1-5 Host/Subnet Quantities for Class A IP Addresses Number of Bits Subnet Mask Effective Subnets Effective Hosts 2 255.192.0.0 2 4,194,302 3 255.224.0.0 6 2,097,150 4 255.240.0.0 14 1,048,574 5 255.248.0.0 30 524,286 6 255.252.0.0 62 262,142 7 255.254.0.0 126 131,070 8 255.255.0.0 254 65,534 0323FMf.book Page 24 Wednesday, March 12, 2003 9:41 AM
IP Addressing 25 Number of Bits Subnet Mask Effective Subnets Effective Hosts 9 255.255.128.0 510 32,766 10 255.255.192.0 1022 16,382 11 255.255.224.0 2046 8190 12 255.255.240.0 4094 4094 13 255.255.248.0 8190 2046 14 255.255.252.0 16,382 1022 15 255.255.254.0 32,766 510 16 255.255.255.0 65,534 254 17 255.255.255.128 131,070 126 18 255.255.255.192 262,142 62 19 255.255.255.224 524,286 30 20 255.255.255.240 1,048,574 14 21 255.255.255.248 2,097,150 6 22 255.255.255.252 4,194,302 2 Table 1-6 Host/Subnet Quantities for Class B IP Addresses Number of Bits Subnet Mask Effective Subnets Effective Hosts 2 255.255.192.0 2 16,382 3 255.255.224.0 6 8190 4 255.255.240.0 14 4094 5 255.255.248.0 30 2046 6 255.255.252.0 62 1022 7 255.255.254.0 126 510 8 255.255.255.0 254 254 9 255.255.255.128 510 126 10 255.255.255.192 1022 62 11 255.255.255.224 2046 30 12 255.255.255.240 4094 14 13 255.255.255.248 8190 6 14 255.255.255.252 16,382 2 Table 1-5 Host/Subnet Quantities for Class A IP Addresses (Continued) 0323FMf.book Page 25 Wednesday, March 12, 2003 9:41 AM
26 Chapter 1: Networking and Routing Fundamentals NOTE You can derive the maximum number of hosts in each of the address classes by doing the following calculation: N.H.H.H for H * H * H = total number of hosts, where (256 * 256 * 256) – 2 = 16 million, N is the network number, and H is the host. (The calculation actually results in 16,777,214 but is rounded to 16 million.) Figure 1-9 shows the various IP address classes by network and host components. Figure 1-9 IP Addresses by Class The IP addresses that are assigned to most networks have been broken into parts that logically relate to the different areas of each network. For example, part of an IP address identifies a particular network, part identifies a subnet (that is, a subnetwork), and part identifies a specific host within that subnetwork (that is, a host). Table 1-7 Host/Subnet Quantities for Class C IP Addresses Number of Bits Subnet Mask Effective Subnets Effective Hosts 2 255.255.255.192 2 62 3 255.255.255.224 6 30 4 255.255.255.240 14 14 5 255.255.255.248 30 6 6 255.255.255.252 62 2 Class C Class B Class A Network 0 1 Network 0 1 1 24 7 No. Bits 16 14 21 8 64 32 16 8 4 2 1 128 Network 0 Host Host Host Host Host Network Host Network Network 0323FMf.book Page 26 Wednesday, March 12, 2003 9:41 AM
IP Addressing 27 Role of IP Addresses IP uses a hierarchical addressing structure.A router simply sends the packet to the next hop in the route to reach its destination. For example, if a packet has a destination IP address of 172.24.50.10, the router begins with the first octet (172) and searches its routing tables for it. When a match is found, the router then adds the next octet (24) to its search until enough information is learned so that the router can send the packet to its next destination. This router behavior is known as the longest match rule. If the router does not have enough information to route the packet, the packet is dropped. Routers make their hierarchical decisions based on the network and host components of an IP address, as demonstrated in Figure 1-10. Figure 1-10 Example of a Hierarchical IP Address Another good example of the hierarchical addressing technique used by routers is your phone number. For example, if the phone number 919-779-xxxx is dialed, the phone system knows that 919 is located in North Carolina, 779 is in the Raleigh area, and the last four numbers are assigned to a residence. An interesting side note here is that the telephone system is also running out of numbers, hence the implementation of the new toll-free extension, 888. Even in the use of phone numbers, you can see how technology has depleted the “bank” of possible numbers as a result of the use of modems, pagers, cellular phones, personal 800 numbers, and multiple phone lines in a residence. How IP Addresses Are Read Routers examine the most significant or left-most bit of the first octet when determining the class of a network address. This technique of reading IP addresses (also known as the first octet rule) is discussed further as the different classes of addresses are defined. A router usually has an interface to which it connects. This interface is assigned an IP address and subnet mask. Devices trying to reach a host within the network that are assigned to that interface are routed through the interface. For example, consider a Token Network Host Network or IP Address Class aka Prefix IP address 32 bits in length Class A address is 8 bits long and always starts with 0 Class B address is 16 bits long and always starts with 10 Class C address is 24 bits long and always starts with 110 0323FMf.book Page 27 Wednesday, March 12, 2003 9:41 AM
28 Chapter 1: Networking and Routing Fundamentals Ring interface with an IP address of 172.24.248.100. The router knows that packets going into or coming out of network 172.24.0.0 need to interact with this interface. IP Subnet Addressing The need for subnetting has resulted in the massive growth of networks in the past decade. As the available address space rapidly continues to shrink, network managers need to use the existing space more efficiently; hence, subnetting was born. Additional benefits to using subnetting are as follows: • Efficient use of available network addresses • Flexibility in planning network growth and design • Capability to contain broadcast traffic • Availability of local administrative control NOTE Broadcast traffic is defined as data packets that are sent to all nodes on a network. Broadcasts are identified by a broadcast address of all 1s. To better understand subnets, consider them to be extensions of the network number. Essen- tially, you are reassigning part of what is officially the host address space to act as an additional network address. Use the following steps to assign addresses in a subnetted network: Step 1 Define the subnet mask. Step 2 Assign an address to each subnet. Step 3 Assign IP addresses to each node. In many organizations, subnets divide one large network into a number of smaller networks. For example, the previously mentioned Class B network (172.24.0.0) can be subdivided into 256 subnets: 172.24.0.0, 172.24.1.0, 172.24.2.0, and so on. Each subnet would have 254 hosts per subnet. NOTE According to RFC 1812, Section 5.3.5.3, all-subnet broadcast is no longer supported, so an all 1s subnet is now allowed. 0323FMf.book Page 28 Wednesday, March 12, 2003 9:41 AM
IP Addressing 29 Subnet Masking Subnet masks use the same representation technique that regular IP addresses use. However, the subnet mask has binary 1s in all bits that specify the network field. Essen- tially, a subnet mask is a 32-bit number that is applied to an IP address to override the default network or node address convention. The subnet mask also tells the router which octets of an IP address to pay attention to when comparing the destination address of a packet to its routing table. For example, for the subnet 172.24.1.0 to be properly configured, you must apply a mask of 255.255.255.0. This gives you a complete IP subnet address of 172.24.1.0255.255.255.0. If you were to then apply this to an Ethernet interface of a router, and a packet came into the router with a destination address of 172.24.1.30, the router would be able to route the packet appropriately because it knows (through the assigned IP address and mask) that any packet destined for the network 172.24.1.0 is to be sent out the router’s Ethernet interface. All class addresses have default subnet masks because the subnet bits come from the high- order bits of the host field. The following list provides the default subnet masks that are used for each class of IP address: • Class A—255.0.0.0 default mask • Class B—255.255.0.0 default mask • Class C—255.255.255.0 default mask These default masks have a binary 1 in every position that corresponds to the default network address component of the appropriate IP address class. Now that you are familiar with the technical explanation of subnet masking, further discussion is in terms that are easier to understand. The most important thing to remember about subnet masks is that you cannot assign IP addresses with no consideration. The question then becomes, “Why should I use subnetting on my network?”You should do so to route across your network. Then you might ask, “Why route?” Complicated and convoluted, isn’t it? For the purpose of this discussion, assume that you have a large Ethernet segment that is so full of users that the collisions occurring on it are negatively impacting the users’ and the segments’performance. The easy fix is to use a bridge that enables you to split the network but retain connectivity. The problem here is that bridges use MAC addresses to make decisions on where to forward packets. However, if the bridge does not know where to send a packet, it resorts to broadcasting it to everyone. Your slow, busy Ethernet segment will have been split into two segments; your network performance should increase as a result. The problem is that as you begin to connect more segments, you end up with broadcasts flowing all across the network to the point that the intranet might come to a standstill. Large amounts of broadcasts, such as those described here, are typically called broadcast storms, which are a bad thing. What is needed is a piece of hardware with more intelligence—the router, which can segment multiple broadcast domains. 0323FMf.book Page 29 Wednesday, March 12, 2003 9:41 AM
30 Chapter 1: Networking and Routing Fundamentals In general terms, the router connects multiple networks and makes decisions on if it should forward packets based on the packets’ addresses. The router has been designed to drop all packets if it does not know where to forward them; hence, there are no more out-of-control broadcasts. For example, suppose you have network 172.24.0.0 out interface #1 of your router and network 10.37.0.0 out interface #2. First, IP addresses must be assigned to each router interface—assume xxx.xxx.1.1—and at least one PC would need to be on each network. Figure 1-11 demonstrates this scenario. Figure 1-11 Basic Subnetting Example A router does not learn about every available address. Instead, the router believes that if interface 1 has an IP address of 172.24.1.1255.255.0.0, all packets destined for the 172.24.0.0 network must be located on that interface. To recap, if the router receives a packet that is not destined to either of the networks it knows about (in this case, 172.24.0.0 or 10.37.0.0), that packet is dropped (erased) from the router’s memory. If PC A is trying to communicate with PC B, the packet’s destination IP address will be 10.37.100.212. So, how does the router know that this IP address is located in the same network as the IP address that is assigned to its interface (10.37.1.1)? Simply put, the subnet mask must be entered. Therefore, when you assign the IP address 10.37.1.1 to interface 2, you must also specify a subnet mask. TIP Every interface in a router must be assigned a local subnet mask. Fortunately, Cisco routers do not accept an IP address without a mask. If you assigned a subnet mask of 255.255.0.0 to interface 2, you are telling the router when it needs to make a routing decision on a packet if the first two octets of the destination IP address match (10.37). The router then forwards the packet out interface 2. This is because, when designing a subnet mask, 255 in a subnet mask indicates that the router needs an exact match, whereas 0 means that this octet’s value is not important. If you give that interface a subnet mask of 255.255.255.0, you are telling the router to look only at the first three octets of the destination IP address when it needs to make a routing Interface #1 172.24.1.1 Interface #2 10.37.1.1 IP address 172.24.50.10 is assigned to this PC IP address 10.37.100.212 is assigned to this PC PC-A PC-B Router 0323FMf.book Page 30 Wednesday, March 12, 2003 9:41 AM
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  • 1. Ospf Network Design Solutions 2nd Edition 2nd Edition Tom Thomas download https://ebookbell.com/product/ospf-network-design-solutions-2nd- edition-2nd-edition-tom-thomas-2418648 Explore and download more ebooks at ebookbell.com
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  • 5. Cisco Press 201 West 103rd Street Indianapolis, IN 46290 USA Cisco Press OSPF Network Design Solutions Second Edition Thomas M.Thomas II, CCIE No. 9360 0323FMf.book Page i Wednesday, March 12, 2003 9:41 AM
  • 6. ii OSPF Network Design Solutions, Second Edition Thomas M. Thomas II Copyright© 2003 Cisco Systems, Inc. Published by: Cisco Press 201 West 103rd Street Indianapolis, IN 46290 USA All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the publisher, except for the inclusion of brief quotations in a review. Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 First Printing April 2003 Library of Congress Cataloging-in-Publication Number: 2001095162 ISBN: 1-58705-032-3 Warning and Disclaimer This book is designed to provide information about the Open Shortest Path First (OSPF) protocol. Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied. The information is provided on an “as is” basis. The authors, Cisco Press, and Cisco Systems, Inc. shall have neither liability nor responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book or from the use of the discs or programs that may accompany it. The opinions expressed in this book belong to the author and are not necessarily those of Cisco Systems, Inc. Trademark Acknowledgments All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Cisco Press or Cisco Systems, Inc. cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. Feedback Information At Cisco Press, our goal is to create in-depth technical books of the highest quality and value. Each book is crafted with care and precision, undergoing rigorous development that involves the unique expertise of members from the professional technical community. Readers’ feedback is a natural continuation of this process. If you have any comments regarding how we could improve the quality of this book, or otherwise alter it to better suit your needs, you can contact us through email at feedback@ciscopress.com. Please make sure to include the book title and ISBN in your message. We greatly appreciate your assistance. 0323FMf.book Page ii Wednesday, March 12, 2003 9:41 AM
  • 7. iii Publisher John Wait Editor-In-Chief John Kane Cisco Representative Anthony Wolfenden Cisco Press Program Manager Sonia Torres Chavez Manager, Marketing Communications, Cisco Systems Scott Miller Cisco Marketing Program Manager Edie Quiroz Executive Editor Brett Bartow Acquisitions Editor Amy Moss Production Manager Patrick Kanouse Development Editor Christopher Cleveland Project Editor San Dee Phillips Copy Editor Progressive Publishing Alternatives Technical Editors Henry Benjamin, Matthew Birkner, Rick Burts, Daniel Golding, John Hammond, Cary Riddock Team Coordinator Tammi Ross Book Designer Gina Rexrode Cover Designer Louisa Adair Indexer Tim Wright 0323FMf.book Page iii Wednesday, March 12, 2003 9:41 AM
  • 8. iv 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 Communica- tion and Services). Formerly with the Cisco Systems CCIE global team, Henry is now an independent consultant for a large security firm in Australia. He has served as a proctor for the CCIE Lab exams and is the 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. 0323FMf.book Page iv Wednesday, March 12, 2003 9:41 AM
  • 9. v 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 to keep me going. I want to reaffirm a few words of special meaning to my wife and I who have been married for over 15 years… Always Forever Endlessly Until Eternity Acknowledgments I am very grateful to the group of talented people that were assembled to make this book a reality. Through their knowledge, dedication, and hard work, this book has become more than I ever thought possible. The most important acknowledgment must go to my wife, Rose, who put up with me writing all night after working all day. Her unwavering support was the single greatest factor in my ability to complete the book you now hold in your hands. 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. 0323FMf.book Page v Wednesday, March 12, 2003 9:41 AM
  • 10. vi 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 Index 724 0323FMf.book Page vi Wednesday, March 12, 2003 9:41 AM
  • 11. vii 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 0323FMf.book Page vii Wednesday, March 12, 2003 9:41 AM
  • 12. viii 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 0323FMf.book Page viii Wednesday, March 12, 2003 9:41 AM
  • 13. ix 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 0323FMf.book Page ix Wednesday, March 12, 2003 9:41 AM
  • 14. x 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 0323FMf.book Page x Wednesday, March 12, 2003 9:41 AM
  • 15. xi 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 0323FMf.book Page xi Wednesday, March 12, 2003 9:41 AM
  • 16. xii 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 0323FMf.book Page xii Wednesday, March 12, 2003 9:41 AM
  • 17. xiii 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 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 450 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 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 0323FMf.book Page xiii Wednesday, March 12, 2003 9:41 AM
  • 18. xiv 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 0323FMf.book Page xiv Wednesday, March 12, 2003 9:41 AM
  • 19. xv 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 0323FMf.book Page xv Wednesday, March 12, 2003 9:41 AM
  • 20. xvi 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 0323FMf.book Page xvi Wednesday, March 12, 2003 9:41 AM
  • 21. xvii 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 Router Bridge Hub DSU/CSU Catalyst Switch Multilayer Switch ATM Switch ISDN/Frame Relay Switch Communication Server Gateway Access Server PC PC with Software Sun Workstation Macintosh Terminal File Server Web Server Cisco Works Workstation Printer Laptop IBM Mainframe Front End Processor Cluster Controller 0323FMf.book Page xvii Wednesday, March 12, 2003 9:41 AM
  • 22. xviii 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. • Boldface indicates 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 0323FMf.book Page xviii Wednesday, March 12, 2003 9:41 AM
  • 23. xix Introduction OSPF is in use in numerous networks worldwide. OSPF is also one of the most widely tested on proto- 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 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-StateAdvertisement (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. 0323FMf.book Page xix Wednesday, March 12, 2003 9:41 AM
  • 24. xx • 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. 0323FMf.book Page xx Wednesday, March 12, 2003 9:41 AM
  • 25. 0323FMf.book Page xxi Wednesday, March 12, 2003 9:41 AM
  • 26. 0323FMf.book Page 2 Wednesday, March 12, 2003 9:41 AM
  • 27. I P A R T OSPF Fundamentals and Communication Chapter 1 Networking and Routing Fundamentals Chapter 2 Introduction to OSPF Chapter 3 OSPF Communication 0323FMf.book Page 3 Wednesday, March 12, 2003 9:41 AM
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  • 29. C H A P T E R 1 Networking and Routing Fundamentals Achievement: Unless you try to do something beyond what you have already mastered, you will never grow.—Successories In recent years, the growth of networks everywhere has accelerated as many organizations move into the international business arena and join the Internet community. This expansion continues to drive the development, refinement, and complexity of network equipment and software, consequently resulting in some unique issues and exciting advances. You rarely see an advertisement that does not contain the famous www prefix. In my hometown, one 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. 0323FMf.book Page 5 Wednesday, March 12, 2003 9:41 AM
  • 30. 6 Chapter 1: Networking and Routing Fundamentals Figure 1-1 Moore’s Law Foundations of Networking Many advanced features are being supported by the physical hardware through the appli- cation of Moore’s law. Those of us responsible for networking these many devices follow a theoretical framework that allows the required functionality to be deployed within our networks. This framework is more commonly known as the OSI reference model. 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. 100,000 10,000 1000 100 10 1 4004 8086 80,286 80,386 80,486 Intel CPUs 2.5 years Thousands of Transistors Year: 1975 1980 1985 1990 1995 2000 Doubling time of fitted line is 2.0 years. P5 (Pentium) P6 (Pentium Pro) P7 (Merced) 0323FMf.book Page 6 Wednesday, March 12, 2003 9:41 AM
  • 31. Foundations of Networking 7 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. 0323FMf.book Page 7 Wednesday, March 12, 2003 9:41 AM
  • 32. 8 Chapter 1: Networking and Routing Fundamentals 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 Transport Layer *Provides error free and reliable packet delivery *Fragments and reassembles packets while managing network layer connections 4 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 Simple Mail Transfer Protocol (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 Protocol (XDR) Light Weight Presentation 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 Routing Protocol (IGRP) Open Shortest Path First (OSPF) Next Hop Routing Protocol (NHRP) CMOT CMIP over TCP X Windows Hewlett Packard Network 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 System (DNS) To NetBIOS To IPX To ISO- TP To DLSW SSP Radius Remote Authentication Dial-In User Service User Datagram Protocol (UDP) Transport Control Protocol (TCP) Internet Protocol (IP) 802.2 Logical Link Control Ethernet Ethernet V.2 Token Bus Token Ring FDDI 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, RTP, RSVP, RTCP, CLNP, ISO 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 VG- AnyLAN 100 BASET 100 BASEF 1 BASE5 G. 703 PLCP 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 StarLAN 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) 0323FMf.book Page 8 Wednesday, March 12, 2003 9:41 AM
  • 33. Understanding the Seven Layers of the OSI Reference Model 9 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. Upper Layers The upper layers of the OSI reference model—5, 6, and 7—are concerned with application issues. They are generally implemented only in software programs. The application layer is the highest layer and is closest to the end user. Both users and application layer processes interact with software programs that contain a communications component so that the application can interact with the OSI model effectively. The sections that follow review the functions of each upper layer in detail. 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 inter- action between the mail application (cc:Mail, MS Outlook, and so on) or communications package (Secure CRT for Telnet or FTPVoyager for FTP) and the user occurs. For example, Table 1-1 Mnemonics Used to Remember OSI Layers OSI Layer (Upper to Lower) Mnemonic OSI Layer (Lower to Upper) Mnemonic Application (Layer 7) All Physical (Layer 1) Please Presentation (Layer 6) people Data Link (Layer 2) do Session (Layer 5) seem Network (Layer 3) not Transport (Layer 4) to Transport (Layer 4) take Network (Layer 3) need Session (Layer 5) sales Data Link (Layer 2) data Presentation (Layer 6) peoples Physical (Layer 1) processing Application (Layer 7) advice 0323FMf.book Page 9 Wednesday, March 12, 2003 9:41 AM
  • 34. 10 Chapter 1: Networking and Routing Fundamentals 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 communi- 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 5—Session The session layer responsibilities range from managing the application layer’s transfer of information to the data transport portion of the OSI reference model. An example is Sun’s or Novell’s Remote Procedure Call (RPC), which uses Layer 5. Lower Layers The lower layers of the OSI reference model—1, 2, 3, and 4—handle data transport issues. The physical and data link layers are implemented in hardware and software. The other lower layers are generally implemented only in software. These lower layers are the ones that network engineers and designers need to focus on to be successful. The sections that follow review the functions of each of the lower layers in detail. 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. 0323FMf.book Page 10 Wednesday, March 12, 2003 9:41 AM
  • 35. Understanding the Seven Layers of the OSI Reference Model 11 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 ProtocolAddressing.” 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 Organi- 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. 0323FMf.book Page 11 Wednesday, March 12, 2003 9:41 AM
  • 36. 12 Chapter 1: Networking and Routing Fundamentals 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. Figure 1-3 Detailed OSI Layer Relationships Table 1-2 Example Ethernet Address Organization Unique ID Assigned by Cisco 00 00 0C 01 23 45 Application 7 OSI Layer Name of Unit Exchanged Presentation 6 Session 5 Transport 4 Network 3 Data Link 2 Physical Application Presentation Session Transport Network Data Link Physical Host A Host B APDU PPDU SPDU Segment (TCP) Datagram (UDP) Packet Frame Bit 1 Communication subnet boundary Transport Internal Subnet Protocol Session Presentation Application Router Router Network Data Link Physical Network Data Link Physical Protocol Data Unit 0323FMf.book Page 12 Wednesday, March 12, 2003 9:41 AM
  • 37. OSI Reference Model Layers and Information Exchange 13 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,thedataportionofaninformationunitatagivenOSIlayercanpotentiallycontainheaders, 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. Figure 1-4 OSI Packet Encapsulation Through the OSI Layers 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 0323FMf.book Page 13 Wednesday, March 12, 2003 9:41 AM
  • 38. 14 Chapter 1: Networking and Routing Fundamentals 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 forARPAnet, 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. Figure 1-5 OSI Model–to–TCP/IP Mappings 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 0323FMf.book Page 14 Wednesday, March 12, 2003 9:41 AM
  • 39. TCP/IP Protocol Suite 15 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 0323FMf.book Page 15 Wednesday, March 12, 2003 9:41 AM
  • 40. 16 Chapter 1: Networking and Routing Fundamentals • 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. Alter- 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: • 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 network-acces- sible equipment, which are, in turn, interconnected to form your network. The most common types of LANs are as follows: • 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. 0323FMf.book Page 16 Wednesday, March 12, 2003 9:41 AM
  • 41. Types of Network Topologies 17 • 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. Figure 1-6 Typical Ethernet LAN For further information on this subject, visit the following website: www.ethermanage.com/ethernet/ethernet.html Wide-Area Networks WANs are used to connect physically separated applications, data, and resources, thereby extending the reach of your network to form an intranet. The ideal result is seamless access to remote resources from geographically separated end users. The most common types of WAN connectivity technologies include the following: • 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 0323FMf.book Page 17 Wednesday, March 12, 2003 9:41 AM
  • 42. 18 Chapter 1: Networking and Routing Fundamentals • 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 theWorldWideWeb. 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 anANSI 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. 0323FMf.book Page 18 Wednesday, March 12, 2003 9:41 AM
  • 43. Types of Network Topologies 19 • 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. Figure 1-7 Available WAN Technology Options 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. WANOptions Dedicated Switched LeasedLines: FractionalT1/E1 T1/E1 T3/E3 Circuit Switched Packet/Cell Switched BasicTelephone Service ISDN Switched56 X.25 FrameRelay (PVCs&SVCs) ATM SMDS CableModems DSL 0323FMf.book Page 19 Wednesday, March 12, 2003 9:41 AM
  • 44. 20 Chapter 1: Networking and Routing Fundamentals *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. Table 1-3 Carrier Rates and Transmission Characteristics* Digital Signal (DS) Name Circuit Bit Rate Number of DS0s Used Equivalent T-Carrier Name Equivalent E-Carrier Name DS0 64 Kbps 1 - - DS1 1.544 Mbps 24 T-1 - - 2.048 Mbps 32 - E-1 DS1C 3.152 Mbps 48 - - DS2 6.312 Mbps 96 T-2 - - 8.448 Mbps 128 - E-2 - 34.368 Mbps 512 - E-3 DS3 44.736 Mbps 672, or 28 DS1s T-3 - - 139.264 Mbps 2048 - E-4 DS4/NA 139.264 Mbps 2176 - - DS4 274.176 Mbps 4032 - - - 565.148 Mbps 4 E-4 Channels - E-5 SONET Signal Bit Rate SDH Signal SONET Capacity SDH Capacity OC–1 (STS-1) 51.84 Mbps STM–0 28 DS–1s or 1 DS–3 21 E1s OC–3 (STS-3) 155.52 Mbps STM–1 84 DS–1s or 3 DS–3s 63 E1s or 1 E4 OC–12 (STS–12) 622.08 Mbps STM–4 336 DS–1s or 12 DS–3s 252 E1s or 4 E4s OC–48 (STS–48) 2.488 Gbps STM–16 1344 DS–1s or 48 DS–3s 1008 E1s or 16 E4s OC–192 (STS–192) 10 Gbps STM–64 5376 DS–1s or 192 DS–3s 4032 E1s or 64 E4s OC-256 13.271 Gbps - - - OC-768 40 Gbps - - - 0323FMf.book Page 20 Wednesday, March 12, 2003 9:41 AM
  • 45. IP Addressing 21 IP Addressing This section discusses IP addressing methodology, basic subnetting, variable-length subnet masking (VLSM), and classless interdomain routing (CIDR). In a properly designed and configured network, communication between hosts and servers is transparent. This is because each device that uses the TCP/IP protocol suite has a unique 32-bit IP address. A device reads the destination IP address in the packet and makes the appropriate routing decision based on this information. In this case, a device might be either the host or server using a default gateway or a router using its routing table to forward the packet to its destination. Regardless of what the device is, the communication is easily accomplished and transparent to the user as a result of proper IP addressing. IP addresses can be represented as a group of four decimal numbers, each within the range of 0 to 255. Each of these four decimal numbers is separated by a decimal point. The method of displaying these numbers is known as dotted decimal notation. Note that these numbers can also be displayed in both the binary and hexadecimal numbering systems. Figure 1-8 illustrates the basic format of an IP address as determined by using dotted decimal notation. Figure 1-8 IP Address Format as Determined by Dotted Decimal Notation IP addresses have two primary logical components, network and host portions, the difference and use of which is extremely important. A third component, the subnet, is also used. A network address identifies the logical network and must be unique; if the network is to be a part of the Internet, the network must be assigned by American Registry for Internet Numbers (ARIN) in North America, Réseaux IP Européens (RIPE) in Europe, and Asia Pacific Network Information Centre (APNIC) in Asia. A host address, on the other hand, identifies a host (device) on a network and is assigned by a local administrator. ! # 0323FMf.book Page 21 Wednesday, March 12, 2003 9:41 AM
  • 46. 22 Chapter 1: Networking and Routing Fundamentals Consider a network that has been assigned an address of 172.24. An administrator then assigns a host the address of 248.100. The complete address of this host is 172.24.248.100. This address is unique because only one network and one host can have this address. NOTE In many cases when dealing with advanced networking topics such as OSPF, the latest trend is to write IP addresses as follows: x.x.x.x/8 or /16 or /24. This has become an accepted method of shorthand for IP addressing. The number to the right of the slash (/) represents the number of bits in the subnet mask. Class A Addresses In a Class A address (also known as /8), the first octet contains the network address and the other three octets make up the host address. The first bit of a Class A network address must be set to 0. Although mathematically it would appear that there are 128 possible Class A network addresses (the first bit is set to 0), the address 00000000 is not available, so there are only 127 such addresses. This number is further reduced because network 127.0.0.0 is reserved for loopback addressing purposes and 10.0.0.0 is a reserved private range. This means that only 126 ClassA addresses are available for use. However, each ClassA address can support 126 networks that correspond to 16,777,214 node addresses per Class A address. NOTE IP addresses or masks of either all 1s or all 0s in each octet are not usually allowed or used in a classful network implementation. The introduction of CIDR now allows most service providers to assign addresses in /19 or /20. Cisco has made exceptions in using all 1s or all 0s, but for this discussion, consider this practice as being not allowed. Class B Addresses In a Class B (also known as /16) address, the network component uses the first two octets for addressing purposes. The first 2 bits of a Class B address are always 10; that is, 1 and 0, not ten. The address range would then be 128.0.0.0 to 191.255.255.255. This makes available the first 6 bits of the first octet and all 8 bits of the second octet, thereby providing 16,384 possible Class B network addresses. The remaining octets are used to provide over 65,534 hosts per Class B address. 0323FMf.book Page 22 Wednesday, March 12, 2003 9:41 AM
  • 47. IP Addressing 23 Class C Addresses In a Class C (also known as /24) address, the first three octets are devoted to the network component. The first 3 bits of a Class C address must be 110. The address range would then be 192.0.0.0 to 223.255.255.255. This leaves 5 bits of the first octet and 8 bits of the second and third octets, thereby providing 2,097,152 possible Class C addresses. The node address is determined by the last octet, which provides 254 nodes per network. Class D Addresses Class D addresses are special addresses that do not refer to individual networks. The first 4 bits of these addresses are 1110. The address range would then be in the range of 224 to 239. Class D addresses are used for multicast packets, which are used by many different protocols to reach multiple groups of hosts (such as ICMP router discovery or Internet group membership protocol [IGMP], which is gaining in popularity since its release in Cisco IOS Software Release 11.2). Consider these addresses as being preprogrammed within the logical structure of most network components in that when they see a destination address of this type within a packet, the address triggers a response. For example, if a host sends a packet out to the destination IP address 224.0.0.5, all routers (using OSPF) on this address’s Ethernet segment respond. Class E Addresses Addresses in the range of 240.0.0.0 to 255.255.255.255 are termed Class E addresses. The first octet of these addresses begins with the bits 1111. These addresses are reserved for future additions to the IP addressing scheme. These future additions might or might not come to fruition with the advent of IP version 6 (IPv6). In most networks, the assigned IP addresses have been broken into parts that logically relate to different areas. For example, part of an IP address identifies a particular network, part identifies a subnet (that is, subnetwork), and part identifies a specific host within that subnetwork (that is, a subnet). The following three blocks of IP address space for private networks have been reserved according to RFC 1918, “Address Allocation for Private Internets”: • 10.0.0.0–10.255.255.255—Single Class A network numbers • 172.16.0.0–172.31.255.255—Contiguous Class B network numbers • 192.168.0.0–192.168.255.255—Contiguous Class C network numbers NOTE You can also write these three networks as 10/8, 172.16/12, and 192.168/16, using the slash method to represent the address. 0323FMf.book Page 23 Wednesday, March 12, 2003 9:41 AM
  • 48. 24 Chapter 1: Networking and Routing Fundamentals How IP Addresses Are Used Routers examine the most significant or left-most bit of the first octet when determining the class of a network address. This technique of reading IP addresses (also known as the first octet rule) is discussed further as the different classes of addresses are defined. Table 1-4 provides information regarding the different IP address classes. Note that in the format column, N equals the network number and H equals the host number.Also, for Class A addresses, one address is reserved for the broadcast address and one address is reserved for the network. Tables 1-5 through 1-7 list the number of hosts and subnets for Class A, B, and C IP addresses. For the subnets and hosts, all 0s and 1s are excluded. Table 1-4 IP Address Quick-Reference Information Class Format Purpose High- Order Bit Address Range Network/ Host Bits Maximum Number of Hosts A N.H.H.H Large organizations 0 1.0.0.0– 126.255.255.255 7/24 16,777,214 (224 – 2) B N.N.H.H Medium organizations 10 128.0.0.0– 191.255.255.255 14/16 65,534 (216 – 2) C N.N.N.H Small organizations 110 192.0.0.0– 223.255.255.255 22/8 254 (28– 2) D N/A Multicast 1110 224.0.0.0– 239.255.255.255 N/A N/A E N/A Experimental 11110 240.0.0.0– 254.255.255.255 N/A N/A Table 1-5 Host/Subnet Quantities for Class A IP Addresses Number of Bits Subnet Mask Effective Subnets Effective Hosts 2 255.192.0.0 2 4,194,302 3 255.224.0.0 6 2,097,150 4 255.240.0.0 14 1,048,574 5 255.248.0.0 30 524,286 6 255.252.0.0 62 262,142 7 255.254.0.0 126 131,070 8 255.255.0.0 254 65,534 0323FMf.book Page 24 Wednesday, March 12, 2003 9:41 AM
  • 49. IP Addressing 25 Number of Bits Subnet Mask Effective Subnets Effective Hosts 9 255.255.128.0 510 32,766 10 255.255.192.0 1022 16,382 11 255.255.224.0 2046 8190 12 255.255.240.0 4094 4094 13 255.255.248.0 8190 2046 14 255.255.252.0 16,382 1022 15 255.255.254.0 32,766 510 16 255.255.255.0 65,534 254 17 255.255.255.128 131,070 126 18 255.255.255.192 262,142 62 19 255.255.255.224 524,286 30 20 255.255.255.240 1,048,574 14 21 255.255.255.248 2,097,150 6 22 255.255.255.252 4,194,302 2 Table 1-6 Host/Subnet Quantities for Class B IP Addresses Number of Bits Subnet Mask Effective Subnets Effective Hosts 2 255.255.192.0 2 16,382 3 255.255.224.0 6 8190 4 255.255.240.0 14 4094 5 255.255.248.0 30 2046 6 255.255.252.0 62 1022 7 255.255.254.0 126 510 8 255.255.255.0 254 254 9 255.255.255.128 510 126 10 255.255.255.192 1022 62 11 255.255.255.224 2046 30 12 255.255.255.240 4094 14 13 255.255.255.248 8190 6 14 255.255.255.252 16,382 2 Table 1-5 Host/Subnet Quantities for Class A IP Addresses (Continued) 0323FMf.book Page 25 Wednesday, March 12, 2003 9:41 AM
  • 50. 26 Chapter 1: Networking and Routing Fundamentals NOTE You can derive the maximum number of hosts in each of the address classes by doing the following calculation: N.H.H.H for H * H * H = total number of hosts, where (256 * 256 * 256) – 2 = 16 million, N is the network number, and H is the host. (The calculation actually results in 16,777,214 but is rounded to 16 million.) Figure 1-9 shows the various IP address classes by network and host components. Figure 1-9 IP Addresses by Class The IP addresses that are assigned to most networks have been broken into parts that logically relate to the different areas of each network. For example, part of an IP address identifies a particular network, part identifies a subnet (that is, a subnetwork), and part identifies a specific host within that subnetwork (that is, a host). Table 1-7 Host/Subnet Quantities for Class C IP Addresses Number of Bits Subnet Mask Effective Subnets Effective Hosts 2 255.255.255.192 2 62 3 255.255.255.224 6 30 4 255.255.255.240 14 14 5 255.255.255.248 30 6 6 255.255.255.252 62 2 Class C Class B Class A Network 0 1 Network 0 1 1 24 7 No. Bits 16 14 21 8 64 32 16 8 4 2 1 128 Network 0 Host Host Host Host Host Network Host Network Network 0323FMf.book Page 26 Wednesday, March 12, 2003 9:41 AM
  • 51. IP Addressing 27 Role of IP Addresses IP uses a hierarchical addressing structure.A router simply sends the packet to the next hop in the route to reach its destination. For example, if a packet has a destination IP address of 172.24.50.10, the router begins with the first octet (172) and searches its routing tables for it. When a match is found, the router then adds the next octet (24) to its search until enough information is learned so that the router can send the packet to its next destination. This router behavior is known as the longest match rule. If the router does not have enough information to route the packet, the packet is dropped. Routers make their hierarchical decisions based on the network and host components of an IP address, as demonstrated in Figure 1-10. Figure 1-10 Example of a Hierarchical IP Address Another good example of the hierarchical addressing technique used by routers is your phone number. For example, if the phone number 919-779-xxxx is dialed, the phone system knows that 919 is located in North Carolina, 779 is in the Raleigh area, and the last four numbers are assigned to a residence. An interesting side note here is that the telephone system is also running out of numbers, hence the implementation of the new toll-free extension, 888. Even in the use of phone numbers, you can see how technology has depleted the “bank” of possible numbers as a result of the use of modems, pagers, cellular phones, personal 800 numbers, and multiple phone lines in a residence. How IP Addresses Are Read Routers examine the most significant or left-most bit of the first octet when determining the class of a network address. This technique of reading IP addresses (also known as the first octet rule) is discussed further as the different classes of addresses are defined. A router usually has an interface to which it connects. This interface is assigned an IP address and subnet mask. Devices trying to reach a host within the network that are assigned to that interface are routed through the interface. For example, consider a Token Network Host Network or IP Address Class aka Prefix IP address 32 bits in length Class A address is 8 bits long and always starts with 0 Class B address is 16 bits long and always starts with 10 Class C address is 24 bits long and always starts with 110 0323FMf.book Page 27 Wednesday, March 12, 2003 9:41 AM
  • 52. 28 Chapter 1: Networking and Routing Fundamentals Ring interface with an IP address of 172.24.248.100. The router knows that packets going into or coming out of network 172.24.0.0 need to interact with this interface. IP Subnet Addressing The need for subnetting has resulted in the massive growth of networks in the past decade. As the available address space rapidly continues to shrink, network managers need to use the existing space more efficiently; hence, subnetting was born. Additional benefits to using subnetting are as follows: • Efficient use of available network addresses • Flexibility in planning network growth and design • Capability to contain broadcast traffic • Availability of local administrative control NOTE Broadcast traffic is defined as data packets that are sent to all nodes on a network. Broadcasts are identified by a broadcast address of all 1s. To better understand subnets, consider them to be extensions of the network number. Essen- tially, you are reassigning part of what is officially the host address space to act as an additional network address. Use the following steps to assign addresses in a subnetted network: Step 1 Define the subnet mask. Step 2 Assign an address to each subnet. Step 3 Assign IP addresses to each node. In many organizations, subnets divide one large network into a number of smaller networks. For example, the previously mentioned Class B network (172.24.0.0) can be subdivided into 256 subnets: 172.24.0.0, 172.24.1.0, 172.24.2.0, and so on. Each subnet would have 254 hosts per subnet. NOTE According to RFC 1812, Section 5.3.5.3, all-subnet broadcast is no longer supported, so an all 1s subnet is now allowed. 0323FMf.book Page 28 Wednesday, March 12, 2003 9:41 AM
  • 53. IP Addressing 29 Subnet Masking Subnet masks use the same representation technique that regular IP addresses use. However, the subnet mask has binary 1s in all bits that specify the network field. Essen- tially, a subnet mask is a 32-bit number that is applied to an IP address to override the default network or node address convention. The subnet mask also tells the router which octets of an IP address to pay attention to when comparing the destination address of a packet to its routing table. For example, for the subnet 172.24.1.0 to be properly configured, you must apply a mask of 255.255.255.0. This gives you a complete IP subnet address of 172.24.1.0255.255.255.0. If you were to then apply this to an Ethernet interface of a router, and a packet came into the router with a destination address of 172.24.1.30, the router would be able to route the packet appropriately because it knows (through the assigned IP address and mask) that any packet destined for the network 172.24.1.0 is to be sent out the router’s Ethernet interface. All class addresses have default subnet masks because the subnet bits come from the high- order bits of the host field. The following list provides the default subnet masks that are used for each class of IP address: • Class A—255.0.0.0 default mask • Class B—255.255.0.0 default mask • Class C—255.255.255.0 default mask These default masks have a binary 1 in every position that corresponds to the default network address component of the appropriate IP address class. Now that you are familiar with the technical explanation of subnet masking, further discussion is in terms that are easier to understand. The most important thing to remember about subnet masks is that you cannot assign IP addresses with no consideration. The question then becomes, “Why should I use subnetting on my network?”You should do so to route across your network. Then you might ask, “Why route?” Complicated and convoluted, isn’t it? For the purpose of this discussion, assume that you have a large Ethernet segment that is so full of users that the collisions occurring on it are negatively impacting the users’ and the segments’performance. The easy fix is to use a bridge that enables you to split the network but retain connectivity. The problem here is that bridges use MAC addresses to make decisions on where to forward packets. However, if the bridge does not know where to send a packet, it resorts to broadcasting it to everyone. Your slow, busy Ethernet segment will have been split into two segments; your network performance should increase as a result. The problem is that as you begin to connect more segments, you end up with broadcasts flowing all across the network to the point that the intranet might come to a standstill. Large amounts of broadcasts, such as those described here, are typically called broadcast storms, which are a bad thing. What is needed is a piece of hardware with more intelligence—the router, which can segment multiple broadcast domains. 0323FMf.book Page 29 Wednesday, March 12, 2003 9:41 AM
  • 54. 30 Chapter 1: Networking and Routing Fundamentals In general terms, the router connects multiple networks and makes decisions on if it should forward packets based on the packets’ addresses. The router has been designed to drop all packets if it does not know where to forward them; hence, there are no more out-of-control broadcasts. For example, suppose you have network 172.24.0.0 out interface #1 of your router and network 10.37.0.0 out interface #2. First, IP addresses must be assigned to each router interface—assume xxx.xxx.1.1—and at least one PC would need to be on each network. Figure 1-11 demonstrates this scenario. Figure 1-11 Basic Subnetting Example A router does not learn about every available address. Instead, the router believes that if interface 1 has an IP address of 172.24.1.1255.255.0.0, all packets destined for the 172.24.0.0 network must be located on that interface. To recap, if the router receives a packet that is not destined to either of the networks it knows about (in this case, 172.24.0.0 or 10.37.0.0), that packet is dropped (erased) from the router’s memory. If PC A is trying to communicate with PC B, the packet’s destination IP address will be 10.37.100.212. So, how does the router know that this IP address is located in the same network as the IP address that is assigned to its interface (10.37.1.1)? Simply put, the subnet mask must be entered. Therefore, when you assign the IP address 10.37.1.1 to interface 2, you must also specify a subnet mask. TIP Every interface in a router must be assigned a local subnet mask. Fortunately, Cisco routers do not accept an IP address without a mask. If you assigned a subnet mask of 255.255.0.0 to interface 2, you are telling the router when it needs to make a routing decision on a packet if the first two octets of the destination IP address match (10.37). The router then forwards the packet out interface 2. This is because, when designing a subnet mask, 255 in a subnet mask indicates that the router needs an exact match, whereas 0 means that this octet’s value is not important. If you give that interface a subnet mask of 255.255.255.0, you are telling the router to look only at the first three octets of the destination IP address when it needs to make a routing Interface #1 172.24.1.1 Interface #2 10.37.1.1 IP address 172.24.50.10 is assigned to this PC IP address 10.37.100.212 is assigned to this PC PC-A PC-B Router 0323FMf.book Page 30 Wednesday, March 12, 2003 9:41 AM
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