This section provides a brief introduction to end to end protection for SR-TE LSPs. See Seamless BFD for SR-TE LSPs for more detailed description of protection switching using Seamless BFD and a configured failure-action.
End-to-end protection for SR-TE LSPs is provided using secondary or standby paths. Standby paths are permanently programmed in the data path, while secondary paths are only programmed when they are activated. S-BFD is used to provide 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, then 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 may be combined with local protection, but it is recommended that the S-BFD control packet timers be set to 1 second or more to allow sufficient time for any local protection action for a segment to complete without triggering S-BFD to go down on the end to end LSP path.
To prevent failure between the paths of an SR-TE LSP, that is to avoid, for example, a failure of a primary path that affects its standby backup path, then disjoint paths should be configured or the srlg command configured on the secondary paths.
As with RSVP-TE LSPs, SR-TE standby paths support the configuration of a path preference. This value is used to select the standby path to be used when more than one available path exists.
For more details of end to end protection of SR-TE LSPs with S-BFD, see section Seamless BFD for SR-TE LSPs.