A shared risk link group (SRLG) represents a set of interfaces (or links) that share the same risk of failing because they may be subjected to the same resource failures or defects. Two examples where the same risk of failure exists are fiber links that share the same conduit, and multiple wavelengths that share the same fiber.
SRLGs are supported by both LSP redundancy protection and FRR protection. SRLGs allow the user to prepare a detour route that is disjoint from the primary LSP path. See Disjoint and Non-disjoint Paths.
The SRLG feature ensures that a primary and secondary LSP path, or a bypass tunnel or detour LSP path, do not share SRLGs. That is, they do not share the same sets of links that are considered to have a similar (or identical) chance of failure.
To use SRLGs, the user first creates an SRLG by assigning one or more routers to the SRLG. Then, the user links the SRLG to an MPLS interface and enables the SRLG feature on the LSP path. SRLGs cannot be assigned to the system interface.