MPLS LDP Session Protection
Table of Contents
Introduction
LDP Session Protection is an optimization feature. It is used when directly connected LDP peer sessions become unavailable but still have IP reachability over a different path. LDP bindings are kept in the LIB to save time from full synchronization when the direct connections comes back up.
LDP Session Protection
- There are two types of LDP connections:
- Direct LDP Session - directly connected LSR, one hop away.
- Targeted LDP Session - not directly connected LSR, multiple hops away.
- By default if the directly connected LDP session loses connectivity to its peer, all bindings are flushed from the LIB. When interfaces come up and LDP sessions are re-established, LDP has to synchronize it's label bindings.
- LDP Session Protection is an optimization, when enabled, will not flush the LIB when direct LDP sessions go down. As long as there exists another path to the LDP Peer, it will maintain the LIB synchronized using Targeted LDP Session. IGP will cause a reroute, but the label bindings will still be present from the old peer. When interfaces come back up, LDP will not need to synchronize since it maintains the state using the targeted sessions.
- Feature has to be configured for both ends or if not possible have the other end accept targeted hellos using command mpls ldp discovery targeted-hello accept.
- Below are some outputs from session protections:
- One parameter is to specify which peers to establish the session protection. It limits it using an ACL and the for command.
- Another parameters specifies how long to keep the session protected using the command durations.
Relevant Commands
mpls ldp session protection
Configures the session protection. Two parameters exist: for and duration. With For you can specify an ACL with peer neighbors. With durations, you can specify how long to keep the session up in protected mode.
R1(config)# mpls ldp session protection [for (acl)]
R1(config)# mpls ldp session protection [duration (<30-2147483>| infinate)]
mpls ldp discovery targeted-hello accept
Allows for targeted hellos if enabling session protection is not possible on one end.
R1(config)# mpls ldp discovery targeted-hello accept [for (acl)]
show mpls ldp discovery detail
Shows all LDP sessions including Targeted LDP Sessions
show mpls ldp discovery detail
sh mpls ldp neighbor detail
Show session protection
sh mpls ldp neighbor (IP) detail