IGP shortcuts are an MPLS functionality where LSPs are treated like physical links within IGPs; that is, LSPs can be used for next-hop reachability. If an RSVP-TE LSP is used as a shortcut by OSPF or IS-IS, it is included in the SPF calculation as a point-to-point link for both primary and LFA next hops. It can also be advertised to neighbors so that the neighboring nodes can also use the links to reach a destination via the advertised next hop.
IGP shortcuts can be used to simplify remote LFA support and simplify the number of LSPs required in a ring topology.
When both IGP shortcuts and LFA are enabled under OSPF or IS-IS, and LDP FRR is also enabled, the following applies:
a FEC that is resolved to a direct primary next hop can be backed up by a tunneled LFA next hop
a FEC that is resolved to a tunneled primary next hop does not have an LFA next hop; it relies on RSVP-TE FRR for protection