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Configuring ECMP-Aware BFD for RSVP LSPs

When you configure BFD for a FEC, a BFD session is established for only one active local next-hop for the router. 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.) RSVP 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.

RSVP 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 RSVP 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 RSVP LSP traceroute returns an error (for example, a timeout), all the BFD sessions associated with that FEC are torn down.

To configure RSVP to establish BFD sessions for all ECMP paths configured for the specified FEC, include the ecmp statement. If you configure the ecmp statement, you must also configure the periodic-traceroute statement for the specified FEC. If you do not do so, the commit fails. You can configure the periodic-traceroute statement at the global hierarchy level ([edit protocols ldp oam]) while only configuring the ecmp statement for a specific FEC ([edit protocols ldp oam fec address bfd-liveness-detection]).




ecmp;

For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.

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