BGP (Border Gateway Protocol), currently in version 4, is the routing protocol used between AutonomousSystems in the Internet. Also called Interdomain Routing.
- BGP is not necessarily concerned about finding the best route, it's primary concern is just reachability information.
- An AS number is a 16-bit number.
- Information exchanged between BGP routers includes entire routes essentially including an AS path, so that BGP routers can ensure that they are not sending a packet on a loop.
- BGP uses TCP (reliable) to exchange information with other routers so that it can be sure that information is recieved. In this way it only needs to send routing information when routing information changes.