Definition

BGP (Border Gateway Protocol)

BGP (Border Gateway Protocol) is a protocol for exchanging routing information between gateway hosts (each with its own router) in a network of autonomous systems. BGP is often the protocol used between gateway hosts on the Internet. The routing table contains a list of known routers, the addresses they can reach, and a cost metric associated with the path to each router so that the best available route is chosen.

Hosts using BGP communicate using the Transmission Control Protocol (TCP) and send updated router table information only when one host has detected a change. Only the affected part of the routing table is sent. BGP-4, the latest version, lets adminstrators configure cost metrics based on policy statements. (BGP-4 is sometimes called BGP4, without the hyphen.)

BGP communicates with autonomous (local) networks using Internal BGP (IBGP) since it doesn't work well with IGP. The routers inside the autonomous network thus maintain two routing tables: one for the interior gateway protocol and one for IBGP.

BGP-4 makes it easy to use Classless Inter-Domain Routing (CIDR), which is a way to have more addresses within the network than with the current IP address assignment scheme.

BGP is a more recent protocol than the Exterior Gateway Protocol (EGP).

Also see the Interior Gateway Protocol (IGP) and the Open Shortest Path First (OSPF) interior gateway protocol.

 

Getting started with BGP
To explore how BGP is used in the enterprise, here are some additional resources:
BGP essentials: The protocol that makes the Internet work: BGP literally makes the Internet work. That, along with its complexity, makes it essential to know how to troubleshoot problems quickly.
Advanced BGP network design for stability and security: Working with BGP in an IP network can challenge even the best network engineers. Mastering it will yield a more stable and secure network.

Contributor(s): Cho Man Fai and Cameo Wood, Natalie
This was last updated in July 2007
Posted by: Margaret Rouse

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