Abstract: A repeater selecting unit selects at least one repeater that becomes a notification destination of route information for routing a malicious packet through a defense device, from among a plurality of repeaters adjacent to the defense device, based on the information on the attack. A route-information notifying unit notifies the route information for routing the malicious packet through the defense device to the selected repeater. A packet control unit controls a passage of the malicious packet routed to the defense device from the repeater to which the route information has been notified.

Abstract: A gate device acquires authorized address information indicating a source address of a non-attacking packet transmitted by an authorized device, i.e., an address issuing server, provided on a network. The gate device generates normal condition information indicating conditions for the non-attacking packet based on the authorized address information acquired, and does not allow passage of an attacking packet while allowing passage of a non-attacking packet. The non-attacking packet is one that satisfies the conditions indicated in the normal condition information.