Appendix D. Border Gateway Protocol 4 Basics of Operation

Border Gateway Protocol version 4 (BGP-4, or just BGP), is an exterior gateway routing protocol used between routing domains or autonomous systems. BGP is the protocol used between all Internet service providers and in the cores of other large networks.

BGP provides extremely stable routing between autonomous systems even with huge routing tables. It also provides network administrators with a great deal of control over routing decisions.