Frr Behavior - Nokia 7705 SAR-W Series Manual

MPLS Guide
The periodic bypass reoptimization feature evaluates only the PSBs of the PLRs
associated with that bypass LSP and only against the new bypass LSP path. The
background re-evaluation task will, however, audit all PSBs on the system against all
existing manual and dynamic bypass LSPs. PSBs that have not been moved by the
dynamic or manual re-optimization of a bypass LSP, due to the PSB constraints not
being met by the new signaled bypass LSP path, will be re-evaluated by the
background task against all existing manual and dynamic bypass LSPs.
The background re-evaluation task also checks for PSBs that have requested a
node-protect bypass LSP but are currently associated with a link-protect bypass
LSP, as well as PSBs that have requested FRR protection and have no association.
The background task is in addition to the attempt made when an RESV message is
received on the protected LSP path, which ensures the association is completed
faster.
This feature is not supported with inter-area dynamic bypass LSPs.

3.7.3 FRR Behavior

The FRR MPLS facility backup method and one-to-one backup method are
configured on the ingress LER (iLER) by using the fast-reroute command.
The behavior of an LSP at an iLER with both FRR and a standby LSP path configured
is as follows.
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• When a downstream detour route (alternative path) becomes active at a Point
of Local Repair (PLR):
The iLER switches to the standby LSP path as soon as it is notified of the
reroute. If the primary LSP path is subsequently repaired at the PLR, the LSP
switches back to the primary path. If the standby path goes down, the LSP is
switched back to the primary path, even though the primary path is still on the
detour route at the PLR.
• If the primary path goes down at the iLER while the LSP is on the standby path,
the detour route at the iLER is torn down and, for one-to-one backup detour
routes, a "path tear" is sent for the detour route. In other words, the detour route
at the iLER does not protect the standby LSP. If and when the primary LSP is
again successfully resignaled, the iLER detour route will be restarted.
• When the primary LSP fails at the iLER:
The LSP switches to the detour route. If the primary path undergoes a global
revertive recovery, the LSP switches back to the primary path. If the LSP is on
the detour route and the detour route fails, the LSP is switched to the standby
path.
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