Acronym for
Border Gateway Protocol.
Routing involves two basic activities: determination of optimal routing paths and the transport of packets through an internetwork. The transport of packets through an internetwork is relatively straightforward. Path determination, on the other hand, can be very complex. BGP is a protocol that addresses the task of path determination.
BGP performs interdomain routing in TCP/IP networks. BGP is an exterior gateway protocol (EGP), which means that it performs routing between multiple autonomous systems and exchanges routing and reachability information with other BGP systems.
BGP performs three types of routing: interautonomous system routing, intra-autonomous system routing, and pass-through autonomous system routing.
Interautonomous system routing occurs between two or more BGP routers in different autonomous systems. Peer routers in these systems use BGP to maintain a consistent view of the internetwork topology. BGP neighbors communicating between autonomous systems must reside on the same physical network. The Internet serves as an example of an entity that uses this type of routing because it is comprised of autonomous systems. Many of these represent the various institutions, corporations, and entities that make up the Internet. BGP is frequently used to provide path determination to provide optimal routing within the Internet.
Intra-autonomous system routing occurs between two or more BGP routers located within the same autonomous system. Peer routers within the same autonomous system use BGP to maintain a consistent view of the system topology. BGP also is used to determine which router will serve as the connection point for specific external autonomous systems. Once again, the Internet provides an example of interautonomous system routing. An organization, such as a university, could make use of BGP to provide optimal routing within its own administrative domain or autonomous system. The BGP protocol can provide both inter- and intra-autonomous system routing services.
Pass-through autonomous system routing occurs between two or more BGP peer routers that exchange traffic across an autonomous system that does not run BGP. In a pass-through autonomous system environment, the BGP traffic did not originate within the autonomous system in question and is not destined for a node in the autonomous system. BGP must interact with whatever intra-autonomous system routing protocol is being used to successfully transport BGP traffic through that autonomous system.
I had a rather odd dream, where I was helping a troop of
Girl Scouts debug some problems with
BGP. The neighbor keeps toggling between
idle and
active, see. I figure either the
AS number is wrong, or the
update-source command is missing. It turns out, instead, that
the Cisco is configured to act as a scented candle. I explain this, and they thank me.