End-To-End Protection; Seamless Bfd For Sr-Te Lsps - Nokia 7705 SAR-W Series Manual

MPLS and RSVP-TE
This behavior is supported in the SR shortest path tunnel feature at both the LER and
LSR. An SR-TE LSP that transits at an LSR and that matches the ILM of a
downstream node SID automatically takes advantage of this protection when
enabled. If required, node SID protection can be disabled under the IGP instance by
excluding the prefix of the SID node from LFA.
3.12.5.2
This section provides a brief introduction to end-to-end protection for SR-TE LSPs.
See
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.
Note: The 7705 SAR does not support shared risk link groups (SRLGs) for SR-TE. If the
active/standby paths are not explicitly hopped throughout the network, they might merge
into a single point of failure.

3.12.6 Seamless BFD for SR-TE LSPs

The 7705 SAR supports seamless BFD (S-BFD). Unlike LSP BFD, S-BFD does not
rely on the traditional BFD session bootstrapping process or session state at the tail
end of a session. Instead, when S-BFD is initialized the system selects a set of
discriminators for the reflector or initiator function.
108

End-to-End Protection

Seamless BFD for SR-TE LSPs
Use subject to Terms available at: www.nokia.com
for detailed information on protection switching
© 2022 Nokia.
MPLS Guide
3HE 18686 AAAB TQZZA