Tunnels are established between nodes along a packet transfer route in a communication network so that a packet is transferred from a first relay node to a second relay node via one or more intermediate relay nodes using the established tunnels. An intermediate relay node receives, from an adjacent downstream relay node, a reply message storing relay-node addresses identifying the downstream relay node and at least one intermediate relay node between the downstream relay node and the first relay node. The intermediate relay node establishes a tunnel to the downstream relay node in association with the relay-node address of the downstream relay node, updates the reply message by removing the relay-node address of the down stream relay node from the reply message, and transfers the updated reply message to an adjacent upstream relay node along the packet transfer route.