Routing protocols that have been designed to run within a single administrative domain (IGPs) generally do so by assigning a metric to each link and then choosing@ as the installed path between two nodes@ the path for which the total distance (sum of the metric of each link along the path) is minimized. BGP@ designed to provide routing over a large number of independent administrative domains (autonomous systems)@ does not make its path-selection decisions through the use of a metric. It is generally recognized that any attempt to do so would incur significant scalability problems as well as interadministration coordination problems. However@ there are deployments in which a single administration runs several contiguous BGP networks. In such cases@ it can be desirable@ within that single administrative domain@ for BGP to select paths based on a metric@ just as an IGP would do. The purpose of this document is to provide a specification for doing so.
RFC 7311-2014 history
2014RFC 7311-2014 The Accumulated IGP Metric Attribute for BGP