Technology - IP Routing & Addressing Crisis 3 - RIB & BGP

Synopsis

We discuss the BGP routing protocol and the Routing Information Base in which each router maintains large amounts of information relating to how best to forward packets. This is the aspect of routers and of the whole BGP system which is the most important limiting factor in the scalability of the current architecture. We also discuss stability problems such as ‘path hunting’ which add to the burden of all BGP routers.

Table of Contents

• 1. Synopsis
• 2. Introduction
• 3. The BGP routing system
  • 3.1 Routers handling both IPv4 and IPv6 packets
  • 3.2 Autonomous System networks
  • 3.3 IGP, eBGP and iBGP terminology
  • 3.4 Multihoming
• 4. Routers in the Default Free Zone (DFZ)
  • 4.1.1 Singlehomed router’s default path
  • 4.1.2 RIB and FIB burdens of DFZ routers
  • 4.2 Numbers of BGP routers
  • 4.3 The ‘global BGP routing table’
    • 4.3.1 High growth rate
• 5. Routing Information Base (RIB)
  • 5.1 Adj-RIB-In
  • 5.2 Loc-RIB
  • 5.3 Adj-RIB-Out
  • 5.4 Number of peers
    • 6. BGP Stability
      • 6.1 Router decisions unaffected by traffic levels
      • 6.2 Manual configuration of routers
      • 6.3 Frequent changes
      • 6.4 Path hunting
        • 6.4.1 Delays and timers
        • 6.4.2 The MRAI timer and convergence time
        • 6.4.3 Example of path hunting
        • 6.4.4 Delays and unwanted messages
    • 7. Related reports

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