Resource Reservation Protocol (RSVP) association signaling can be
used to bind two unidirectional Label Switched Paths (LSPs) into an
associated bidirectional LSP. When an associated bidirectional LSP
is co-routed, the reverse LSP follows the same path as its forward
LSP. This document updates the fast reroute procedures defined in
RFC 4090 to support both single-sided and double-sided provisioned
associated bidirectional LSPs. This document also updates the
procedure for associating two reverse LSPs defined in RFC 7551 to
support co-routed bidirectional LSPs. The fast reroute procedures
can ensure that, for the co-routed LSPs, traffic flows on co-routed
paths in the forward and reverse directions after a failure event.