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:
Manual bypass disjoint
Manual bypass non-disjoint (eligible only if srlg-frr is non-strict)
Dynamic bypass disjoint
Dynamic bypass non-disjoint (eligible only if srlg-frr is non-strict)
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.