In response to a route-changing event, original routes on the network are changed to new routes. A destination-reachable range is identified as a range from which packets can reach an information processing device specified by a destination address. Modification of forwarding data is performed for a neighbor communication device which is located outside the destination-reachable range and adjacent to a communication device in the destination-reachable range, so as to enable forwarding of packets to that communication device in the destination-reachable range. The modified forwarding data is then transmitted to the neighbor communication device. The modification made to the forwarding data results in an additional destination-reachable range, which is thus added to the destination-reachable range. Another cycle of processing is then performed on the basis of the expanded destination-reachable range.