MPLS LDP Label Retention Mode

The MPLS LDP label retention mode specifies under what conditions the label mappings advertised by any peer will be kept. There are two modes:

• Conservative – Advertised label mappings are retained only if used to explicitly forward packets to their next-hop. These mappings are received from a valid next-hop router.
• Liberal – All advertised label mappings from each peer LSR are kept regardless of whether the peer is a next-hop router or not.

An advantage to using conservative label retention mode is that only labels required for packet forwarding to next-hops are allocated and maintained. An operational disadvantage of conservative mode is that a new label must be obtained from the new next-hop router if routing changes the next-hop for a given destination.

The main advantage of the Liberal Label retention mode is that reaction to routing changes is swift, since labels needed for such changes already exist and maintained. The disadvantage of liberal mode is the large amount of unneeded label mappings that are routinely maintained and distributed.

MPLS LDP label retention mode defaults to liberal.

Use the mpls ldp-label-retention-mode command in global configuration mode on the global router to change the MPLS LDP label retention mode for the router.