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Cisco IP Routing: Packet Forwarding and Intra-domain Routing Protocols

Book Description

As a networking professional, you will find this practical guide an invaluable resource for understanding routing technologies and configuring and troubleshooting Cisco routers, as well as for studying for the CCIE exam. Cisco IP Routing presents the most thorough information available on the inner workings of Cisco routers. Focusing on intra-domain dynamic routing protocols, the book provides an in-depth understanding of IP routing and forwarding technologies, and their implementation within Cisco routers.

You will find essential background information on IP addressing, general routing and forwarding processes, and routing table maintenance. The book discusses packet forwarding and static routing, and details the specific mechanisms inside the dynamic routing protocols, covering both the distance vector and link-state routing protocols. Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), and Enhanced IGRP (EIGRP), Cisco's proprietary routing protocol, are covered in depth within the context of Cisco's implementation.

Specific topics covered include:

  • Variable length subnet masks

  • Classful and classless addressing and routing

  • Routing and forwarding differences

  • Static and dynamic routing

  • Routing table structure and maintenance in Cisco routers

  • Cisco packet switching mechanisms, including fast, optimum, distributed, NetFlow, and Cisco Express Forwarding

  • Cisco load-sharing techniques

  • The Bellman-Ford and Dijkstra algorithms

  • RIP packet formats, input and outbound messaging, event processing, configuration commands, and more

  • IGRP packet formats, input and outbound messaging, events processing, configuration commands, and more

  • Comparison between ISIS and OSPF

  • OSPF subprotocols and packet formats

  • OSPF intra-area, inter-area and external routing

  • OSPF flooding algorithm and link-state database synchronization

  • LSA installation and SPF scheduling

  • OSPF configuration and implementation in Cisco routers

  • EIGRP operation and configuration

  • EIGRP stub router feature

Numerous examples of logs from real Cisco routers illustrate the concepts presented and their practical application. Useful configuration examples are also presented. In addition, many of the chapters include a Frequently Asked Questions section that clarifies common misunderstandings and confusion about IP routing technologies and Cisco routers.

Comprehensive, yet detailed and accessible, Cisco IP Routing provides the inside information you need to be a truly proficient Cisco router networking professional.



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Table of Contents

  1. Copyright
    1. Dedication
  2. Preface
    1. Introduction
    2. Objectives
    3. Audience
    4. Organization
    5. Approach
    6. Disclaimer
  3. One. Overview of Cisco Routers
    1. 1.1. Description of a Cisco Router
    2. 1.2. Interfacing with Routers
    3. 1.3. Router Configuration
    4. 1.4. Monitoring and Troubleshooting Tools
    5. 1.5. The Test Lab
    6. 1.6. References
  4. Two. Review of IP Addressing
    1. 2.1. IP Addressing
    2. 2.2. Subnetting
    3. 2.3. Special Addressing Rules
    4. 2.4. Classful and Classless Addressing
    5. 2.5. Variable-Length Subnet Masks
    6. 2.6. IP Addressing Details in Cisco Routers
    7. 2.7. Frequently Asked Questions
    8. 2.8. References
  5. Three. Routing and Forwarding Processes
    1. 3.1. Packet-Switched Technologies
    2. 3.2. Router Operation Overview
    3. 3.3. Routing Information Sources
    4. 3.4. Static Routing
    5. 3.5. Dynamic Routing
    6. 3.6. Default Routing
    7. 3.7. Basic Forwarding Algorithm
    8. 3.8. Classful Routing Operations
    9. 3.9. Classless Routing Operations
  6. Four. Routing Table Maintenance
    1. 4.1. Routing Information Sources
      1. 4.1.1. Directly Attached Networks and Interface Routes
      2. 4.1.2. Static Routes
      3. 4.1.3. Dynamic Routes
      4. 4.1.4. Comparison of the Route Sources
    2. 4.2. Routing Table Maintenance
      1. 4.2.1. Representation of Routing Information and Interfaces
      2. 4.2.2. Routing Table Structure
      3. 4.2.3. Route Source Selection
      4. 4.2.4. Routing Table Initialization
      5. 4.2.5. Asynchronous Table Maintenance
      6. 4.2.6. Route Resolvability
      7. 4.2.7. Change of an Interface State
      8. 4.2.8. Change of Interface Address
      9. 4.2.9. Dynamic Route Processing
      10. 4.2.10. Static Route Processing
      11. 4.2.11. Manual Routing Table Clearance
      12. 4.2.12. Defining Default Routes
      13. 4.2.13. Default Route Selection
    3. 4.3. Summary
    4. 4.4. Frequently Asked Questions
  7. Five. Packet Forwarding
    1. 5.1. Overview of IP Forwarding
    2. 5.2. Packet Input
    3. 5.3. Forwarding Engine
      1. 5.3.1. Route Lookup
      2. 5.3.2. Policy Routing
    4. 5.4. Packet Delivery
      1. 5.4.1. Network Interface Types
      2. 5.4.2. General Packet-Delivery Functionality
        1. 5.4.2.1. Packet Delivery on Broadcast Interfaces
        2. 5.4.2.2. Packet Delivery on Point-to-Point Interfaces
        3. 5.4.2.3. Packet Delivery on Point-to-Multipoint Interfaces
        4. 5.4.2.4. Packet Delivery on Dialer-Enabled Interfaces
        5. 5.4.2.5. Packet Delivery on Tunnel Interfaces
        6. 5.4.2.6. Packet Delivery on Loopback Interfaces
        7. 5.4.2.7. Packet Delivery on Null Interface
    5. 5.5. Forwarding Methods in Cisco IOS
      1. 5.5.1. Fast Switching
      2. 5.5.2. Autonomous and SSE Switching
      3. 5.5.3. Optimum Switching
      4. 5.5.4. Distributed Switching
      5. 5.5.5. Cisco Express Forwarding
      6. 5.5.6. NetFlow Switching
    6. 5.6. Load Sharing in Cisco IOS
      1. 5.6.1. Per Packet Load Sharing in Process-Switching Path
      2. 5.6.2. Per Destination Load Sharing in Fast Switching Path
      3. 5.6.3. Load Sharing in Cisco Express Forwarding
    7. 5.7. Summary
    8. 5.8. Frequently Asked Questions
    9. 5.9. References
  8. Six. Static Routes
    1. 6.1. Static Routes in Cisco Routers
    2. 6.2. Backup Static Routes
    3. 6.3. Using Static Routes in NBMA and Dial-Up Environments
    4. 6.4. Default Routes
    5. 6.5. Routing Loops and Discard Routes
    6. 6.6. Implementation Scenarios
      1. 6.6.1. ISP and a Customer
      2. 6.6.2. Central Office and Branch Offices (Partial Mesh)
    7. 6.7. Frequently Asked Questions
  9. Seven. Dynamic Routing Protocols in Cisco IOS
    1. 7.1. Common Functionality of Dynamic Routing Protocols
    2. 7.2. Routing Protocol Configuration
    3. 7.3. Routing Protocol Data Structures
    4. 7.4. Route Redistribution
    5. 7.5. Events Processed by Routing Protocols
    6. 7.6. Summary
    7. 7.7. Frequently Asked Questions
    8. References
  10. Eight. Distance-Vector Routing Protocols
    1. 8.1. Distance-Vector Principles
      1. 8.1.1. Topology Discovery
      2. 8.1.2. Counting-to-Infinity Problem
      3. 8.1.3. Split Horizon
      4. 8.1.4. Holddown Timers
      5. 8.1.5. Triggered Updates
      6. 8.1.6. Counting to Infinity Again
      7. 8.1.7. The Bellman-Ford Algorithm
    2. 8.2. Routing Information Protocol
      1. 8.2.1. Basic Description and History
      2. 8.2.2. Configuration Parameters
      3. 8.2.3. Message Format
      4. 8.2.4. Input Processing
      5. 8.2.5. Event Processing
        1. 8.2.5.1. Internal Events
        2. 8.2.5.2. External Events
      6. 8.2.6. Sending RIP Updates
      7. 8.2.7. RIP version 2
        1. 8.2.7.1. Changes to Input Processing
        2. 8.2.7.2. Changes to Message Sending
      8. 8.2.8. RIP Demand Circuit Extensions
      9. 8.2.9. RIP Configuration
        1. 8.2.9.1. Configuration Commands
        2. 8.2.9.2. Configuration Examples
      10. 8.2.10. Summary
      11. 8.2.11. Frequently Asked Questions
    3. 8.3. Interior Gateway Routing Protocol
      1. 8.3.1. Basic Description and History
      2. 8.3.2. Protocol Parameters
      3. 8.3.3. Message Format
      4. 8.3.4. Input Processing
      5. 8.3.5. Event Processing
      6. 8.3.6. IGRP Configuration
        1. 8.3.6.1. Basic IGRP Configuration
        2. 8.3.6.2. Using Unequal-Cost Load Sharing
        3. 8.3.6.3. Redistributing to IGRP
      7. 8.3.7. Summary
      8. 8.3.8. Frequently Asked Questions
    4. 8.4. References
  11. Nine. Link-State Routing Protocols
    1. 9.1. Introduction to Link-State Routing
      1. 9.1.1. Theoretical Basis
      2. 9.1.2. Dijkstra Algorithm
      3. 9.1.3. Database Synchronization and Flooding Algorithm
      4. 9.1.4. Calculating Routing Information
      5. 9.1.5. Overview of Link-State Routing Protocols
    2. 9.2. Open Shortest Path First (OSPF)
      1. 9.2.1. Basic Characteristics
        1. 9.2.1.1. Subprotocols
        2. 9.2.1.2. Structure of OSPF Routing Domain
        3. 9.2.1.3. Types of Routing within an OSPF Domain
        4. 9.2.1.4. Route Aggregation
        5. 9.2.1.5. Convergence Characteristics
      2. 9.2.2. General Data Structures
      3. 9.2.3. Intra-Area Routing
        1. 9.2.3.1. Overview of Intra-Area OSPF Functionality
        2. 9.2.3.2. Types of Networks and Topology Abstraction
          1. Point-to-Point Networks
          2. Broadcast Networks
          3. NBMA Networks
          4. Point-to-Multipoint Networks
          5. Virtual Links
          6. Interfaces in Loopback State
        3. 9.2.3.3. OSPF Transport Protocol and Packet Formats
        4. 9.2.3.4. Options Field
        5. 9.2.3.5. Hello Subprotocol
        6. 9.2.3.6. Interface State Machine
        7. 9.2.3.7. Designated Router Election Algorithm
        8. 9.2.3.8. Adjacencies and Neighbor State Machine
        9. 9.2.3.9. OSPF Topology Abstraction and Types of LSAs
        10. 9.2.3.10. Origination of LSAs
        11. 9.2.3.11. Flooding and LSDB Maintenance Procedures
          1. Sources of New Information
          2. Receiving the LSAs
          3. LSA Installation and SPF Scheduling
          4. Flooding the LSA to Other Neighbors
          5. Special Cases in Flooding Algorithm
          6. LSA Aging, Periodic Checking, and Removal
        12. 9.2.3.12. Routing Table Calculation
        13. 9.2.3.13. Frequently Asked Questions
      4. 9.2.4. Inter-Area Routing
        1. 9.2.4.1. Introduction to Inter-Area Routing and ABR Functionality
        2. 9.2.4.2. Distribution of Routing Information and Types of LSAs
        3. 9.2.4.3. Inter-area Route Calculation
        4. 9.2.4.4. Origination of Summary-LSAs
        5. 9.2.4.5. Virtual Links
        6. 9.2.4.6. Cisco ABR Behavior
        7. 9.2.4.7. Frequently Asked Questions
      5. 9.2.5. Routing to External Networks in OSPF
        1. 9.2.5.1. Introduction and Terminology
        2. 9.2.5.2. Distribution of Routing Information and Types of LSA
        3. 9.2.5.3. Outline of ASBR Functionality
        4. 9.2.5.4. External Route Calculation
        5. 9.2.5.5. Stub and Totally Stub Areas
        6. 9.2.5.6. Not-So-Stubby Areas
        7. 9.2.5.7. Frequently Asked Questions
      6. 9.2.6. Summary of Routing Table Calculation and Route Preference Rules
      7. 9.2.7. Demand Circuit OSPF Extensions
      8. 9.2.8. Details of Cisco OSPF Implementation
        1. 9.2.8.1. Packet Pacing
        2. 9.2.8.2. LSA Group Pacing
        3. 9.2.8.3. SPF Scheduling
        4. 9.2.8.4. Partial SPF Calculation
      9. 9.2.9. OSPF Configuration
        1. 9.2.9.1. Basic OSPF Configuration
        2. 9.2.9.2. General OSPF Parameters
        3. 9.2.9.3. Interface-Specific Parameters
        4. 9.2.9.4. Configuring OSPF on NBMA Media
        5. 9.2.9.5. Basic OSPF ABR Configuration
        6. 9.2.9.6. Configuring Route Aggregation
        7. 9.2.9.7. Configuring Virtual Links
        8. 9.2.9.8. Basic OSPF ASBR Configuration (Route Redistribution)
        9. 9.2.9.9. Aggregation of Redistributed Routes
        10. 9.2.9.10. Configuring Stub Areas
        11. 9.2.9.11. Configuring NSSA
        12. 9.2.9.12. Tuning OSPF Timers
      10. 9.2.10. Configuration Examples
        1. 9.2.10.1. Single-Area OSPF Configuration
        2. 9.2.10.2. Sample Configurations for OSPF over Frame Relay Cloud
        3. 9.2.10.3. Configuration of OSPF with Multiple Areas
        4. 9.2.10.4. Route Redistribution and Stub Areas
        5. 9.2.10.5. NSSA
      11. 9.2.11. Summary
    3. 9.3. References
  12. Ten. Enhanced IGRP
    1. 10.1. Basic Description and History
    2. 10.2. Theoretical Basis
    3. 10.3. Subsystems and Data Structures
    4. 10.4. Message Format
    5. 10.5. Input Processing
      1. 10.5.1. Generic Packet Processing
      2. 10.5.2. Processing EIGRP Updates
      3. 10.5.3. Processing EIGRP Queries
      4. 10.5.4. Processing EIGRP Replies
    6. 10.6. Internal Event Processing
    7. 10.7. Sending EIGRP Packets
      1. 10.7.1. Sending EIGRP Hellos
      2. 10.7.2. Sending Updates and Queries
      3. 10.7.3. Sending Replies
    8. 10.8. Shortest-Path Calculation
    9. 10.9. Default Route Support
    10. 10.10. Route Aggregation
    11. 10.11. EIGRP Stub Router Extension
    12. 10.12. EIGRP Configuration
    13. 10.13. Configuration Examples
      1. 10.13.1. Basic EIGRP Configuration
      2. 10.13.2. Local and Distributed Route Calculation
      3. 10.13.3. Configuring Variance Parameter
      4. 10.13.4. Injecting the Default Route
      5. 10.13.5. Manual Route Summarization
      6. 10.13.6. Route Redistribution, Filtering, and Route Maps
    14. 10.4. Frequently Asked Questions
  13. Bibliography