Abstract: The relationship between cache servers and backup cache servers is dynamically managed, and when a fault has arisen, a second cache server that is close in terms of distance to a PBR router that is forwarding traffic to a first cache server at which the fault has arisen is used as a backup cache server. Also, a module or a device having functionality as a cache manager and a cache agent is prepared, and with the trigger being the detection of a fault in the first cache server, the cache agent automatically alters the traffic forwarding destination of the PBR router, which is forwarding traffic to the first cache server at which the fault has arisen, to be the second cache server that is close in terms of distance to the PBR router.