Configuring ECMP-Aware BFD for LDP LSPs
When you configure BFD for a FEC, a BFD session is established for only one active local next-hop for the router or switch. However, you can configure multiple BFD sessions, one for each FEC associated with a specific equal-cost multipath (ECMP) path. For this to function properly, you also need to configure LDP LSP periodic traceroute. (See Configuring LDP LSP Traceroute.) LDP LSP traceroute is used to discover ECMP paths. A BFD session is initiated for each ECMP path discovered. Whenever a BFD session for one of the ECMP paths fails, an error is logged.
LDP LSP traceroute is run periodically to check the integrity of the ECMP paths. The following might occur when a problem is discovered:
- If the latest LDP LSP traceroute for a FEC differs from the previous traceroute, the BFD sessions associated with that FEC (the BFD sessions for address ranges that have changed from previous run) are brought down and new BFD sessions are initiated for the destination addresses in the altered ranges.
- If the LDP LSP traceroute returns an error (for example, a timeout), all the BFD sessions associated with that FEC are torn down.
To configure LDP to establish BFD sessions for all ECMP paths configured for the specified FEC, include the ecmp statement.
For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.
Along with the ecmp statement, you must also include the periodic-traceroute statement, either in the global LDP OAM configuration (at the [edit protocols ldp oam] or [edit logical-systems logical-system-name protocols ldp oam] hierarchy level) or in the configuration for the specified FEC (at the [edit protocols ldp oam fec address] or [edit logical-systems logical-system-name protocols ldp oam fec address] hierarchy level). Otherwise, the commit operation fails.
