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OSPF: Anatomy of an Internet Routing Protocol

Book Description

Written for TCP/IP network administrators, protocol designers, and network application developers, this book gives the most complete and practical view ever into the inner workings of Internet routing. The book focuses on OSPF (Open Shortest Path First), a common TCP/IP routing protocol that provides robust and efficient routing support in the most demanding Internet environments. A methodical and detailed description of the protocol is offered and OSPF's role within the wider context of a TCP/IP network is demonstrated.

Practical throughout, the book provides not only a theoretical description of Internet routing, but also a real-world look into how theory translates into practice. It shows how algorithms are implemented, and how the routing protocols function in a working network where transmission lines and routers routinely break down.

You will find clear explanations of such routing fundamentals as how a router forwards packets, IP addressing, CIDR (Classless Inter-Domain Routing), the routing table, Internet routing architecture, and the two main routing technologies: Distance Vector and link-state algorithms. OSPF is discussed in depth, with an examination of the rationale behind OSPF's design decisions and how it has evolved to keep pace with the rapidly changing Internet environment. OSPF topics covered by the book include the following:

  • OSPF areas and virtual links

  • NBMA (Nonbroadcast multi-access) and Point-to-MultiPoint network segments

  • OSPF configuration and management

  • Interaction with other routing protocols

  • OSPF cryptographic authentication

  • OSPF protocol extensions, including the Demand Circuit extensions and the multicast extensions to OSPF (MOSPF)

  • An OSPF FAQ

  • IP multicast and multicast routing are also discussed. Methods for debugging routing problems are explained, including a catalog of available debugging tools. The book also offers side-by-side comparisons of all the unicast and multicast routing protocols currently in use in the Internet.

    You will come away from this book with a sophisticated understanding of Internet routing and of the OSPF protocol in particular. Moreover, the book's practical focus will enable you to put this deeper understanding to work in your network environment.



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    Table of Contents

    1. Copyright
    2. List of Tables
    3. List of Figures
    4. Preface
      1. Introduction
      2. Audience
      3. Organization of This Book
      4. Companion Book: OSPF Complete Implementation
      5. Acknowledgments
    5. I. Internet Routing Overview
      1. 1. Role of Routers in the Internet
        1. 1.1. The Internet Protocol Suite
          1. Physical Layer
          2. Data-Link Layer
          3. Network Layer
          4. Transport Layer
          5. Higher Layers
        2. 1.2. Forwarding IP Datagrams
          1. Modification of Forwarding
          2. Sending ICMP Errors
          3. Add-Ons
          4. Finding the First-Hop Router
          5. 1.2.1. IP Addresses
          6. 1.2.2. A Short History of Internet Addressing
          7. 1.2.3. Tunneling
        3. 1.3. IPv6
          1. Differences from IPv4
        4. Further Reading
      2. 2. Internet Routing Protocols
        1. 2.1. Routing Tables
          1. Implementation of Routing Tables
        2. 2.2. Internet Routing Architecture
        3. 2.3. Distance Vector Algorithms
          1. Distance Vector Convergence
          2. Counting to Infinity
          3. Improving Convergence
        4. 2.4. Link-State Algorithms
        5. Further Reading
    6. II. The OSPF Protocol
      1. 3. Developing the OSPF Protocol
        1. 3.1. Functional Requirements
        2. 3.2. Design Decisions
          1. Link-State versus Distance Vector
          2. Link-State Basis
          3. Encapsulation
          4. LSA Fragmentation
          5. Common Mechanisms over Disparate Link Layers
          6. Backup Designated Router
          7. External Route Tag
          8. Hierarchical Abstraction
        3. 3.3. OSPFv1: A False Start
        4. 3.4. Interoperability Testing
          1. Tools
          2. Problems Found
          3. INTEROP Demo
        5. 3.5. Field Trials
          1. Feature Requests
          2. Problems Found
        6. 3.6. On Becoming a Standard
        7. 3.7. The Internet Evolves
          1. CIDR
          2. Frame Relay Subnets
          3. Multicast
          4. Enhanced Security
          5. IPv6
        8. Further Reading
      2. 4. OSPF Basics
        1. 4.1. An OSPF Example
        2. 4.2. Link State Advertisements (LSAs)
          1. 4.2.1. Identifying LSAs
            1. LS Type Field
            2. Links State ID Field
            3. Advertising Router Field
          2. 4.2.2. Identifying LSA Instances
            1. LS Sequence Number Field
          3. 4.2.3. Verifying LSA Contents
            1. LS Checksum Field
          4. 4.2.4. Removing LSAs from the Distributed Database
            1. LS Age Field
          5. 4.2.5. Other LSA Header Fields
            1. Options
            2. Length
        3. 4.3. A Sample LSA: The Router-LSA
        4. 4.4. The link-State Database
        5. 4.5. Communicating between OSPF Routers: OSPF Packets
        6. 4.6. Neighbor Discovery and Maintenance
        7. 4.7. Database Synchronization
          1. 4.7.1. Initial Database Synchronization
          2. 4.7.2. Reliable Flooding
          3. 4.7.3. Flooding Robustness
        8. 4.8. Routing Calculations
        9. Further Reading
        10. Exercise
      3. 5. OSPF Network Types
        1. 5.1. The IP Subnet Model
        2. 5.2. Broadcast Subnets
          1. 5.2.1. Neighbor Discovery and Maintenance
          2. 5.2.2. Database Synchronization
            1. Designated Router Election
          3. 5.2.3. Abstraction
          4. 5.2.4. Problems
        3. 5.3. NBMA Subnets
          1. 5.3.1. Neighbor Discovery and Maintenance
          2. 5.3.2. Database Synchronization
          3. 5.3.3. Abstraction
          4. 5.3.4. Problems
        4. 5.4. Point-to-MultiPoint Subnets
          1. 5.4.1. Neighbor Discovery and Maintenance
          2. 5.4.2. Database Synchronization
          3. 5.4.3. Abstraction
          4. 5.4.4. Problems
        5. Further Reading
        6. Exercises
      4. 6. Hierarchical Routing in OSPF
        1. 6.1. OSPF Areas
          1. 6.1.1. Area Organization
          2. 6.1.2. Virtual Links
        2. 6.2. Incorporating External Routing Information
          1. 6.2.1. Interaction with Areas
        3. 6.3. OSPF Area Types
          1. 6.3.1. Stub Areas
          2. 6.3.2. NSSAs
        4. Further Reading
        5. Exercises
      5. 7. OSPF Extensions
        1. 7.1. TOS-Based Routing
          1. Backward-Compatibility Provisions
        2. 7.2. Stub Areas
          1. Backward-Compatibility Provisions
        3. 7.3. Demand Circuit Extensions
          1. The DoNotAge Bit
          2. Caveats
          3. Backward-Compatibility Provisions
        4. 7.4. NSSA Areas
          1. Backward-Compatibility Provisions
        5. 7.5. Database Overflow Support
          1. Backward-Compatibility Provisions
        6. 7.6. The External-Attributes-LSA
          1. Backward-Compatibility Provisions
        7. Further Reading
        8. Exercises
      6. 8. An OSPF FAQ
    7. III. Internet Multicast Routing
      1. 9. Internet Multicast Routing
        1. 9.1. Internet Multicast Model
        2. 9.2. The Multicast Protocol Stack
          1. IP Multicast Addresses
          2. 9.2.1. IGMP
            1. IGMPv2
            2. IGMPv3
        3. 9.3. Broadcast Forwarding
          1. 9.3.1. Multicast Forwarding
            1. Multicast Router Processing
        4. 9.4. MBONE
          1. TTL Thresholds
        5. Further Reading
      2. 10. MOSPF
        1. 10.1. An Extended Example
          1. 10.1.1. Steady-State Forwarding Behavior
            1. Expanding Ring Search
          2. 10.1.2. Response to Change
        2. 10.2. Group-Membership-LSAs
        3. 10.3. MOSPF Routing Calculations
          1. 10.3.1. The Multicast Forwarding Cache
          2. 10.3.2. Maintaining the Multicast Forwarding Cache
          3. 10.3.3. Calculating a Multicast Datagram’s Path: Details
        4. 10.4. Hierarchical Multicast in MOSPF
          1. 10.4.1. Advertising MOSPF Information in the Presence of Hierarchy
          2. 10.4.2. Routing Calculations in Hierarchical MOSPF
        5. 10.5. Backward Compatibility: Mixing with Nonmulticast Routers
          1. Restrictions
        6. 10.6. MOSPF in the MBONE
        7. Further Reading
        8. Exercises
    8. IV. Configuration and Management
      1. 11. OSPF Management
        1. 11.1. SNMP
        2. 11.2. OSPF MIB
        3. 11.3. Configuring OSPF
          1. 11.3.1. Configuring Link Costs
          2. 11.3.2. Configuring OSPF Areas
          3. 11.3.3. Configuring Timers
        4. 11.4. An Example: The Arkansas Public School Computer Network
        5. 11.5. Monitoring the OSPF Protocol
          1. Synchronization Problems
          2. Checking Database Contents
          3. Other Issues
        6. 11.6. Interactions with Other Routing Protocols
          1. 11.6.1. OSPF/BGP Interaction
            1. Using OSPF to Replace IBGP
          2. 11.6.2. OSPF/RIP Interaction
        7. 11.7. OSPF Security
          1. 11.7.1. OSPF Cryptographic Authentication
          2. 11.7.2. Message Verification
          3. 11.7.3. Key Management
          4. 11.7.4. Stronger Security
        8. Further Reading
        9. Exercises
      2. 12. Debugging Routing Problems
        1. 12.1. War Stories
        2. 12.2. Finding Tools for Debugging Routing Problems
        3. 12.3. Tool Interpretation
        4. 12.4. The ping Tool
          1. How It Works
          2. Strong Points
          3. Weak Points
        5. 12.5. The traceroute Tool
          1. How It Works
          2. Strong Points
          3. Weak Points
        6. 12.6. SNMP MIBs
          1. How It Works
          2. Strong Points
          3. Weak Points
        7. 12.7. MIB-Based Tools
          1. How They Work
          2. Strong Points
          3. Weak Points
        8. 12.8. Network Analyzers
          1. How They Work
          2. Strong Points
          3. Weak Points
        9. 12.9. Protocol-Specific Tools
          1. How They Work
          2. Strong Points
          3. Weak Points
        10. 12.10. Product-Specific Monitoring and Tracing
          1. How They Work
          2. Strong Points
          3. Weak Points
        11. 12.11. Multicast Traceroute
          1. How It Works
          2. Strong Points
          3. Weak Points
        12. Further Reading
        13. Exercises
    9. V. Routing Protocol Comparisons
      1. 13. Unicast Routing Protocols
        1. 13.1. RIP
          1. RIPv2
        2. 13.2. OSPF
        3. 13.3. BGP
          1. IBGP
          2. BGP Path Attributes
          3. BGP Operational Issues
        4. 13.4. IGRP
          1. EIGRP
        5. 13.5. Integrated IS-IS
        6. 13.6. Historical Protocols
        7. 13.7. Interaction among Routing Protocols
        8. Further Reading
      2. 14. Multicast Routing Protocols
        1. 14.1. Broadcast-and-Prune Protocols
        2. 14.2. DVMRP
        3. 14.3. MOSPF
        4. 14.4. PIM Dense
        5. 14.5. PIM Sparse
        6. 14.6. CBT
        7. 14.7. Interaction among Multicast Routing Protocols
    10. Bibliography