Patent ID: 8458338

Claim:
An address translation device disposed on a boundary between a private network and a global network respectively having different address spaces, and mutually connecting the private network and the global network, the address translation device comprising: a port assignment rule storage unit adapted to store a port assignment rule which defines port resources associated with a global address of the address translation device by dividing the port resources between port resources for sending from the private network and port resources for listening from the global network; a session-port assignment table storage unit adapted to store a session-port assignment table showing a correspondence between information indicating an existing session and information indicating the port resource associated with the global address and assigned to a session endpoint of the existing session on a side of the private network; in response to reception of a packet for an existing session in the session-port assignment table, an address translation unit adapted to translate address information of a packet received according to the correspondence between the existing session and the port resource registered in the session-port assignment table, and in response to reception of a packet for opening a new session which is not registered in the session-port assignment table, adapted to translate address information of the packet by making an entry in the session-port assignment table of a correspondence between the new session and a port resource thereof by assigning, the port resource to the new session according to the port assignment rule; and a port assignment rule update unit operable to change in the port assignment rule a port ratio between a number of assigned ports for sending and a number of assigned ports for listening according to predetermined procedures, wherein the port resource comprises a set of an address and a port number used by a protocol in a transport layer and assigned to a session.