Refer to the exhibit. On this MPLS-based network ring, links have failed between router A and router failures formed microloops while the network converged, when A forwarded traffic to B but B forward

TE Fast ReRoute requires RSVP-TE to signal traffic-engineered LSPs, which is a new signaling protocol and violates the constraint of not enabling a new protocol.

IP Fast ReRoute as a standalone choice refers to basic LFA, which cannot always find a qualifying loop-free adjacent neighbor in a ring topology, leaving certain destinations unprotected.

Standard LFA relies on an adjacent next-hop that satisfies the downstream loop-free condition; in a two-node ring segment, no such neighbor may exist, making LFA insufficient without the remote extension.

RLFA extends standard LFA by using an LDP tunnel to reach a remote P-node that guarantees a loop-free path to the destination. In a ring topology, no adjacent LFA-qualifying neighbor may exist, but RLFA resolves this by leveraging LDP - already present in any MPLS network - to reach a suitable repair node. This avoids microloops without introducing any new protocol such as RSVP-TE.