Srlgs For Frr Lsp Paths; Disjoint And Non-Disjoint Paths - Nokia 7705 SAR-W Series Manual

MPLS Guide

3.8.2 SRLGs for FRR LSP Paths

When setting up the FRR bypass or detour LSP, enable the srlg-frr option on FRR
to ensure that CSPF includes the SRLG constraint in its route calculation. CSPF
prunes all links that are in the SRLG being used by the primary LSP during the
calculation of the FRR path. If one or more paths are found, CSPF sets up the FRR
bypass or detour LSP based on the best cost and signals the FRR LSP.
If there is no path found based on the above calculation and the srlg-frr command
has the strict option set, then the FRR LSP is not set up and the MPLS/RSVP-TE
task keeps trying to set up a path. If the strict option is not set, then the FRR LSP is
set up based on the other TE constraints (that is, excluding the SRLG constraint).

3.8.3 Disjoint and Non-disjoint Paths

A path is considered to be SRLG disjoint from a given link (or node) if the path does
not use any links (or nodes) that belong to the same SRLG as the given link (or
node). Eligible disjoint paths are found by CSPF when the SRLG constraint is
included in the CSPF route calculation (referred to as the strict SRLG condition).
When LSP redundancy is used, the secondary LSP is always signaled with a strict
SRLG condition.
When FRR is used, the FRR bypass or detour LSP may have a strict or non-strict
SRLG condition. If the strict option is used with the srlg-frr command, then the
bypass LSP must be on the list of eligible paths found by the CSPF calculation that
included the SRLG constraint. If the strict option is not used, then it is possible for
the bypass or detour LSP to be non-disjoint. The non-disjoint case is supported only
if the SRLG is not strict.
At the PLR, if an FRR tunnel is needed to protect a primary LSP, the priority order for
selecting that FRR tunnel is as follows:
A bypass or a detour LSP path 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 considered in the CSPF calculation.
3HE 18686 AAAB TQZZA
1. Manual bypass disjoint
2. Manual bypass non-disjoint (eligible only if srlg-frr is non-strict)
3. Dynamic bypass disjoint
4. Dynamic bypass non-disjoint (eligible only if srlg-frr is non-strict)
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