(Border Gateway Protocol) The routing protocol that is used to span autonomous systems on the Internet. It is a robust, sophisticated and scalable protocol that was developed by the Internet Engineering Task Force (IETF). BGP4 supports the CIDR addressing scheme, which increased the number of available IP addresses on the Internet. A path vector protocol, BGP was designed to supersede EGP, the original exterior gateway protocol. See autonomous system, CIDR and routing protocol.