Relay device and relay method

An apparatus for relaying packets transferred over a network and discarding an attack packet detected among the packets, the apparatus comprising:

• an inspection-packet outputting unit that outputs, when detecting the attack packet, an inspection packet in which a transmission-source address contained in the attack packet is set as a destination address and a destination address contained in the attack packet is set as a transmission-source address;
• a filter table storing unit that stores, when acquiring a response packet for the inspection packet, a transmission-source address, a destination address, and identification information of an interface, which has received the response packet, that are contained in the response packet, in a filter table in an associated manner;
• a transfer control unit that determines whether to transfer a packet as a transfer object based on the filter table;
• a route-change determining unit that determines whether to change a route on the network where the packet is transferred;
• and
• a request-packet outputting unit that outputs a request packet for requestinq an output of the inspection packet based on a result of determination by the route-change determining unit.