BGP

The Border Gateway Protocol (BGP) is the core routing protocol of the Internet. It works by maintaining a table of IP networks or 'prefixes' which designate network reachability among autonomous systems (AS). It is described as a path vector protocol. BGP does not use traditional IGP metrics, but makes routing decisions based on path, network policies and/or rulesets.

Very large private IP networks like Sago Networks can also make use of BGP. An example would be the joining of a number of large Open Shortest Path First (OSPF) networks where OSPF by itself would not scale to size. Another reason to use BGP would be multihoming a network for better redundancy either to a multiple access points of a single ISP (RFC 1998) or to multiple ISPs.