COMMUNICATION SYSTEM, CONTROL DEVICE AND CONTROL PROGRAM

In a communication system in which a terminal 1 connected to an internal network 5 communicates with an external network 9 through a control device 2 which controls communication, the control device 2 includes an address registration unit 33 which registers a pair of an address of the terminal 1 and an ID, a storage unit 21 which stores a filtering rule that defines a condition to permit or deny the communication of the terminal 1, and a filter unit 22 which determines whether communication of a packet should be permitted or denied, based on a result of comparison between information stored in an address storage area of the packet transmitted from the terminal, and the filtering rule, when the registered ID is contained in the address storage area of the packet, thereby controlling communication of the pack.