Patent ID: 8493989

Claim:
A network device that performs multicast transmission and multicast reception over a first network that has a plurality of network devices, the first network being any one of a ring network and a cascade network, the first network having a first route and a second route, the network device comprising: a storage unit that stores therein in a corresponding manner a drop address that uniquely identifies data transferred in the first network, one bit of a first control data that indicates whether the data is to be forwarded in the first route and one bit of a second control data that indicates whether the data is to be forwarded in the second route, the drop address specifying data to be dropped from the first network to be transferred to a second network that is different from the first network; an address reception unit that receives a registered drop address of a lower network device from the lower network device, the lower network device being a network device that is located downstream of the network device in the first network with respect to data flow direction; an address determining unit that determines whether the registered drop address received by the address reception unit matches with the drop address stored in the storage unit; a set unit that sets one bit of control data indicating that dropped data is to be forwarded when the address determining unit determines the registered drop address matches with the drop address stored in the storage unit, and one bit of control data indicating that dropped data is to be deleted when the address determining unit determines the registered drop address does not match with the drop address stored in the storage unit, the one bit of control data being set, corresponding to the registered drop address, in control data of a route corresponding to the data flow direction out of the first control data or the second control data; and a control unit that receives data from the first network, determines whether received data is to be dropped to be transferred to the second network based on the drop address stored in the storage unit, when determining that the received data is to be dropped, drops the received data, further determines whether dropped data is to be forwarded to the first route based on the one bit of the first control data stored in the storage unit, when determining that the dropped data is to be forwarded to the first route, forwards the dropped data to the first route, and when determining that the dropped data is not to be forwarded, deletes the dropped data, and determines whether dropped data is to be forwarded to the second route based on the one bit of the second control data stored in the storage unit, when determining that the dropped data is to be forwarded to the second route, forwards the dropped data to the second route, and when determining that the dropped data is not to be forwarded.