Border Gateway Protocol

Last Updated : 18-Nov-2020

What is BGP?

BGP is a protocol for exchanging routing information between autonomous networks in order to find the shortest routes for network traffic


  • An AS – is an automonous system which is a logical abstraction of a network
  • AN ASN is autonomous system which uniquely identifies an autonomous system
  • ASNs are allocated by IANA and are allocated in the range 0-65535, where 64512 to 65534 are private
  • iBGP is internal BGP – routing within an AS
  • eGBP is external BGP – routing between ASs

How Does it Work?

  • BGP operates over port 179 using flow control and error correction so it is reliable.
  • Peering must be configurable manually and once set up if communicates network topology to other connected ASs.
  • BCP exchanges the best path information between peers measured in number of hops (path length) and not latency – the path is called ASPATH
  • You can artificially increase the path length to influence BGP not to take that path, e.g. a satellite link, e.g change path for 200,i to 200,200,200,i will case any 2 hop path to be chosen over this path

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