Provider edge link protection for BGP labeled unicast paths

A precomputed protection path can be configured in a Layer 3 VPN such that if a BGP labeled-unicast path between an edge router in one AS and an edge router in another AS goes down, the protection path (also known as the backup path) between alternate edge routers in the two ASs can be used. This is useful in carrier-of-carriers deployments, where a carrier can have multiple labeled-unicast paths to another carrier. In this case, the protection path avoids disruption of service if one of the labeled-unicast paths goes down.