Path Vector Routing Protocol

A path vector protocol is essentially a distance vector protocol that does not rely on the distance to destination to guarantee a loop-free path but instead relies on the analysis of the path itself.

It is typically deployed in environments where it is difficult to guarantee a consistent metric (distance) across the routing domain. The path is accumulated at each router, and carried in each advertisement, so that any router receiving it can validate the loop-free path before propagating the information. BGP4 is the best example of an RP using this technology.

The main drawback is the size of the advertisements, which grow with the number of hops. As far as IPv6 is concerned, BGP4, enhanced with multiprotocol extensions, remains the path vector RP of choice for exchanging IPv6 routes between autonomous systems.