This section provides a brief introduction to end-to-end protection for SR-TE LSPs. See Seamless BFD for SR-TE LSPs for detailed information on protection switching using seamless BFD (S-BFD) and a configured failure action.
The 7705 SAR supports end-to-end protection for SR-TE LSPs using secondary or standby paths. Standby paths (secondary paths with standby enabled) are permanently programmed in the data path, while secondary paths are only programmed when they are activated. S-BFD is used for end-to-end connectivity checking. The failure-action failover-or-down command under the bfd context of the LSP configures a switchover from the currently active path to an available standby or secondary path if the S-BFD session fails on the currently active path. If S-BFD is not configured, the router that is local to a segment can only detect failures of the top SID for that segment.
End-to-end protection with S-BFD can be combined with local protection but it is recommended that the S-BFD control packet timers be set to a value high enough to allow sufficient time for any local protection action for a particular segment to complete without triggering S-BFD to go down on the end-to-end LSP path.
In order to prevent failures between the paths of an SR-TE LSP (for example, to prevent a failure of a primary path that affects its standby backup path), disjoint paths should be configured.