LDP/IGP interoperability is realized through the holddown process and the holdmaxcost process. When the interface goes Up after going Down, IGP first prevents any peer from being established and then suppresses IGP convergence to wait for the LDP session to go Up. In this period, if the LDP session goes Up, IGP-LDP interoperability is realized. When IGP suppresses the establishment of the peer, the LDP remote session can still be set up as long as there is a reachable route. If the LDP session does not go Up after the timeout of the holddown timer, IGP enters the holdmaxcost process, advertising the maximum cost of the route so that the router does not preferentially select this route. In this process, if the LDP session goes Up, IGP begins to advertise normal costs of the route again. Thus, IGP-LDP interoperability is realized.