Path-vector routing protocol

A path vector protocol is a computer network routing protocol in which it maintains the path that update information takes as it diffuses through the network. Updates which have looped through the network and returned to the same node are easily detected and discarded. This algorithm is sometimes used in Bellman-Ford routing algorithms to avoid "Count to Infinity" problems.

It is different from the distance vector routing and link state routing. Back entry in the routing table contains the destination network, the next router and the path to reach the destination.

Path Vector Messages: In the BGP the AS Routers which participate in path vector routing advertise the reachability of networks each router that recieves a path vector message verifies that the advertised path is according to its policy. If yes then the router will modify its routing table and the message before sending to the next neighbor. In the modified message it sends its own AS number and replaces the next router entry with its own identification.

BGP is an example of a path vector protocol. In BGP the routing table maintains the autonomous systems that are traversed in order to reach the destination system. Exterior Gateway Protocol (EGP) does not use path vectors.

Path vector protocols are a class of distance vector protocol in contrast to link state protocol.