Technology - IP Techniques 3 - OPSF, IS-IS & BGP Routing Protocols


The two internal routing protocols OPSF and IS-IS and the Border Gateway Protocol which is used for routing packets between the tens of thousands of Autonomous Systems which comprise the Internet are discussed in this report. Also discussed are transit routers, multihoming, the Default Free Zone (the border and transit routers which make up the core of the Internet) and the rapid growth of the ‘BGP global routing table’.

Table of Contents

  • 1. SynopsiS
  • 2. Introduction
  • 3. Interior Routing Protocols
    • 3.1 Forwarding Information Base (FIB)
    • 3.2 Routing Information Base (RIB)
    • 3.3 Link-state and distance-vector protocols
    • 3.4 IS-IS
    • 3.5 OSPF
  • 4. The global BGP routing system
    • 4.1 Edge networks
    • 4.2 Autonomous systems
      • 4.2.1 Regional Internet Registries (RIRs)
    • 4.3 Transit routers
    • 4.4 Border routers
    • 4.5 Internal and external BGP messages
    • 4.6 Multihoming
    • 4.7 The Default Free Zone (DFZ)
      • 4.7.1 Transit routers
      • 4.7.2 Internal routers
      • 4.7.3 Non-multihomed border routers
      • 4.7.4 Multihomed border routers
    • 4.8 The global BGP routing table
    • 4.9 Efficient allocation of IP addresses versus routability
      • 4.9.1 Restricting size of BGP routes
      • 4.9.2 Route aggregation
  • 5. Border Gateway Protocol (BGP)
    • 5.1 Path vector protocol
    • 5.2 Simplicity and strengths
    • 5.3 Difficulty scaling to large networks
    • 5.4 Problems with frequent updates
    • 5.5 Barrier to increased address utilisation
  • 6. Related reports
  • Exhibit 1 – The five Regional Internet Registries

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Number of pages 12

Status Archived

Last updated 18 Dec 2007
Update History

Analyst: Robin Whittle

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