LDP outbound FEC filtering allows LDP to perform outbound filtering for label advertisement. It gives you the ability to control which FECs can be advertised and to which LDP neighbors. It also reduces the number of labels distributed to neighbors and the number of messages exchanged with peers. Through this feature, LDP scalability and convergence, security, and performance are improved.
LDP performs a hop-by-hop or dynamic path setup in an MPLS network by assigning and distributing labels to routes learned from the underlying IGP routing protocols. By default, LDP distributes all FECs that are learned locally or from LDP neighbors to all other LDP neighbors. When this behavior is not desired, you can configure LDP to perform outbound filtering FEC filtering.
Outbound filtering is achieved by creating a prefix list that specify prefixes whose label mappings can be distributed. The prefix list is applied to an individual LDP neighbor, or globally to all the LDP neighbors. The FECs permitted by the prefix list are accordingly distributed to the specified LDP neighbor or to all LDP neighbors.
MPLS and LDP protocols must be enabled on the router to use this feature.