Patent ID: 7672245

Claim:
A device for detecting a layer 2 loop in a network identified by a first network address that is divided by a layer 3 relay device that relays a packet at layer 3 , the device comprising: a request-packet transmitting unit that transmits a predetermined number of request packets having a non-unicast destination address that can be received by a target network that includes the network identified by the first network address, from a monitoring network identified by a second network address different from the first network address to the network identified by the first network address, through the layer 3 relay device; and a layer 2 loop detecting unit that receives response packets corresponding to the request packets transmitted by the request-packet transmitting unit, through the layer 3 relay device, and detects the layer 2 loop in the target network when number of response packets having same transmission-source address is larger than the number of transmitted request packets, from among the received response packets.