This feature enhances the IP next-hop based MHP backup path calculation specified in RFC 8518 and Multi-homed prefix LFA extensions in SR-OSPF with the addition of the support of an SR repair tunnel. The SR repair tunnel uses a PQ node or a P-Q set to reach the alternate exit ABR or ASBR for external prefixes, or alternate owner router for intra-area anycast prefixes. This capability is in addition to supporting the RFC 8518 algorithm used in the case where the path to prefix P using the alternate exit ABR or ASBR (or alternate owner router) is in the shortest path from the neighbor of the computing node.
This feature applies the computed backup path to SR-OSPF node SID tunnels of external /32 prefixes and to /32 prefixes in the same area as the computing node, and which are advertised by multiple routers (anycast prefixes) in both algorithm 0 and flexible-algorithm numbers. It also extends the protection to any SR-TE LSP or SR policy that uses an SR-OSPF SID of those same prefixes in its configured or computed SID list.
This feature shares the same configuration CLI commands as the MHP LFA feature as described in Multi-homed prefix LFA extensions in SR-OSPF. After the IP next-hop based MHP LFA is enabled, the extensions to compute an SR repair tunnel for the MHP LFA in the case of SR-OSPF are automatically enabled if the user enables TI-LFA or RLFA. The computation reuses the SID list of the primary path or of the TI-LFA or RLFA backup path of the alternate ABR, ASBR, or alternate owner router. The algorithm details are described in the following section.