BGP basic information

BGP Autonomous Systems

  • An AS is a collection of networks under a single technical administration
  • IGP operates within an AS
  • BGP is used between ASs
  • Exchange of loop-free routing info is guaranteed

BGP features

  • Open standard
  • Exterior – designed for Inter-AS Domain Routing
  • Designed to scale huge inter-network like Internet
  • classless (supports VLSM, CIDR, auto and manual summary)
  • updates are incremental and trigger
  • Path vector – bgp is exchanging the routes which carries also the path information attributes.
  • it sends updates to manually defined neighbor as a unicast
  • BGP is application layer protocol and uses TCP (port 179) for reliability
  • Metric – is complicated and is formed from many attributes
  • AD – 20 for external updates (EBGP), 200 internal updates (IBGP)

BGP loop prevention mechanism

  • AS path loop detection – Whenever a router sees its own AS number in route update it will ignore that.

When to use BGP

  • AS working as transit AS – for example ISP
  • AS connected to multiple AS (multi-homed) – Data traffic entering or leaving A.S needs to be manipulated

When not to use BGP

  • if it is single-homed AS
  • lack of resources in your network equipment
  • limited understanding about BGP

 

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