Border Gateway Protocol

BGP is a router protocol in the IP suite designed to exchange network reachability information with BGP systems in other autonomous systems. You use a fully meshed configuration with BGP.

BGP provides routing updates that include a network number, a list of ASs that the routing information passed through, and a list of other path attributes. BGP works with cost metrics to choose the best available path; it sends updated router information only when one host has detected a change, and only the affected part of the routing table is sent.

BGP communicates within one AS using Interior BGP (IBGP) because BGP does not work well with IGP. Thus the routers inside the AS maintain two routing tables: one for the IGP and one for IBGP. BGP uses exterior BGP (EBGP) between different autonomous systems.