The Border Gateway Protocol (BGP) is an Exterior Routing Protocol(ERP) that transmits routing information between autonomous systems( AS). The Border Gateway Protocol (BGP) works with interdomain routing in which the routing takes place between the autonomous systems. The routers inform each other about the available connection paths. The strength of the BGP protocol lies in its ability to combine various optional routing paths into a single routing table.
Like the Exterior Gateway Protocol( EGP), which is superseded by the BGP protocol, the Border Gateway Protocol is a path vector protocol for routing between autonomous systems (ASs). BGP supports a metric and can make intelligent routing decisions. It can interoperate with Open Shortest Path First( OSPF) as an internal routing protocol. In particular, it supports route aggregation of Classless Interdomain Routing( CIDR).
The BGP information contains all the data about the complete path between the autonomous systems. Based on this information, the protocol creates a graph that represents the interconnection of the different autonomous systems and eliminates looping of the routing. The routing update, where a BGP router is connected to other BGP systems, is transmitted using TCP protocol. The metric used by the BGP protocol is based on information assigned to routers by the network administrator during their configuration, as well as physical and transmission parameters. Since each BGP router has route information from others, especially the neighboring BGP routers, each BGP router builds a database for routes to all reachable autonomous systems.
The BGP protocol is described in RFCs 1163 and 1771. In 1991, RFC 1269 published the Border Gateway Protocol (version 3) Management Information Base( MIB). Version 4, which supports CIDR, is currently in use. It is described in RFC 4271 and is suitable for Gigabit Ethernet.
The BGB protocol also exists as Interior-BGP (IBGP) and as Exterior-BGP (EBGP), which performs routing between two autonomous systems (AS).