Question

What is the Border Gateway Protocol (BGP)? Why is it needed? Explain how it works.

Answer 1

Border Gateway Protocol (BGP) is an identical external gateway protocol. It is designed to exchange routing and availability of information among autonomous systems on the Internet.The protocol is frequently classified as a path vector protocol but is sometimes grouped as a distance-vector routing protocol.

Working:

When BGP runs between two gazes in the same autonomous system, it is known as Internal BGP (iBGP). When it runs between dissimilar autonomous systems, it is called External BGP (eBGP). Routers on the edge of one AS, sharing information with another are called border or edge routers and are typically linked directly, while iBGP gazes can be interlinked through other intermediate routers. Other operational topologies are also possible, such as running eBGP gazing inside a VPN tunnel, allowing two distant sites to exchange routing information in a protected and isolated manner. The major difference between iBGP and eBGP gazing is in the way routes that were received from one gaze are propagated to other gazes. For example, new routes learned from an eBGP gaze are naturally reallocated to all other iBGP gazes as well as all eBGP gazes. However, if new routes were learned on an iBGP gazing, then they are re-promoted only to all other eBGP gazes. These route propagation rules efficiently require that all iBGP gazes inside an AS are interconnected in a full mesh.

Filtering routes learned from gazes, their transformation before reorganization to gazes or before testing them into the routing table is naturally controlled via route-maps method. These are basically rules which let the application of certain actions to routes corresponding certain criteria on either entrance or outlet path. These rules can state that the route is to be dropped or otherwise, its attributes are to be customized. It is generally the responsibility of the AS administrator to provide the preferred route-map configuration on a router supporting BGP.