MPLS LDP Session Protection

MPLS LDP Session Protection is a feature of MPLS that protects LDP bindings in the event that a link fails. It uses MPLS LDP Targeted Hellos to to do so.

For example, imagine two directly connected LDP enabled devices that can also reach each other through alternate IP routes in the network. The LDP session that exists between them over their directly connected link is called an LDP Link hello Adjacency. When LDP session protection is enabled, the LDP Targeted Hello Adjacency is also established for the LDP session, via the alternate IP routes.

Thus, if the directly connected link fails, the peers are still reachable through the alternate path, and the LDP session stays up because the targeted hello adjacency still exists between the devices. When the direct link recovers, the session does not need to be reestablished, and LDP bindings do not need to be relearned.

The command to enable this protection is:

mpls ldp session protection