Nokia 7705 SAR-W Series Manual page 175

MPLS Guide
srlg-frr
Syntax srlg-frr [strict]
no srlg-frr
Context config>router>mpls
Description This system-wide command enables or disables the use of the shared risk link group (SRLG)
constraint in the computation of an FRR bypass or detour LSP for any primary LSP path on
the system. When srlg-frr is enabled, CSPF includes the SRLG constraint in the computation
of an FRR bypass or detour LSP for protecting the primary LSP path.
The strict option is a system-wide option that forces the CSPF to consider any configured
SRLG membership lists in its calculation of every LSP path.
CSPF and FRR
CSPF prunes all links with interfaces that belong to the same SRLG as the interface being
protected, where the interface being protected is the outgoing interface at the PLR used by
the primary path.
If one or more paths are found, the MPLS/RSVP-TE task selects one path based on best cost
and signals the setup of the FRR bypass or detour LSP. If no path is found and the user
included the strict option, the FRR bypass or detour LSP is not set up and the MPLS/RSVP-
TE task keeps retrying the request to CSPF. If no path is found and the strict option is
disabled, if a path exists that meets all the TE constraints except the SRLG constraint, then
the FRR bypass or detour LSP is set up.
An FRR bypass or detour LSP is not guaranteed to be SRLG disjoint from the primary path.
This is because only the SRLG constraint of the outgoing interface at the PLR that the primary
path is using is checked.
When the MPLS/RSVP-TE task is searching for an SRLG bypass tunnel to associate with the
primary path of the protected LSP, the task does the following steps.
3HE 18686 AAAB TQZZA
• First, the task checks for any configured manual bypass LSP that has CSPF enabled
and that satisfies the SRLG constraints.
• The task skips any non-CSPF bypass LSP since there is no ERO returned with which to
check the SRLG constraint.
• If no path is found, the task checks for an existing dynamic bypass LSP that satisfies the
SRLG and other primary path constraints.
• If no bypass path is found, then the task makes a request to CSPF to try to create one.
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MPLS and RSVP-TE
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