8.1 Autonomous Systems
8.1.7 BGP and ISP connectivity basics
BGP is an IP exterior routing protocol defined in RFCs 1163, 1267, 1654, and 1655 which guarantees a loop-free interdomain routing system through the exchange of routing information between ASs. BGP differs from IGPs mentioned earlier in the following ways:
  • BGP is a policy-based routing protocol. It does not use technical metrics, but rather makes routing decisions based on network policies.
  • BGP updates are carried in TCP segments. This means IP connectivity must exist between BGP peers and TCP connections must be negotiated between them before updates can be exchanged.