In transport networks, links may share common physical resources, and fast reroute must avoid paths within the same failure domain. We validated TI-LFA selection of Shared Risk Link Group (SRLG) disjoint repair paths in an IS-IS Segment Routing MPLS network with an IPv6 control plane, based on IPv6 SRLG membership advertisements (TLV 139) as described in RFC 8919. The SR-MPLS control plane used IPv6 addressing for loopbacks and links, and nodes advertised IPv6-based Node-SIDs and Adjacency-SIDs through IS-IS.
We first validated local SRLG behavior using a three-node triangle topology consisting of HPE, Arista, and ZTE devices. By failing the direct link between ZTE and Arista, we observed that traffic between them was rerouted through the HPE node, which provided the SRLG-disjoint alternate path, before switching back to the restored direct link after convergence. For the local SRLG case on HPE, we failed the link with metric ten between the two HPE devices; traffic then switched via the Arista node before returning to the HPE-to-HPE link with metric eleven after IS-IS convergence.
For the remote SRLG test, we moved to a four-node square topology using two HPE devices, Arista, and ZTE. After failing the HPE–Arista vertical link, traffic initially used the lowest-metric path, switched immediately to the SRLG-disjoint repair path via Arista, and later returned to the post-convergence path via the alternate HPE–HPE link.