Refer to the exhibit. MPLS is configured in the network. The routers use OSPF to exchange routing information. Hosts connected to routers R1 and R3 use routers R2 and R4 to access servers running a variety of intranet applications. A network engineer must ensure that R1 and R3 retain an LDP session between them to support traffic flow between the hosts and servers. Which task should the engineer perform to provide LDP bindings if the path between R1 and R3 fails?