Patent ID: 7761539

Claim:
A computer system, in which communication is performed using a first IP address with a first netmask having a predetermined number of bits and a second IP address with a second netmask having a number of bits different from that of the first netmask, the computer system comprising: one or more first nodes for performing communication using the first IP address or the second IP address in a network to which the first netmask and the second netmask are applied; one or more second nodes for performing communication using the second IP address and performing communication control among the first nodes; a third node for selectively assigning the first IP address or the second IP address to the first node; and a fourth node for performing communication with the first nodes, wherein: the first IP address is an IP address used for communication between each group including one or more of the first nodes, and the fourth node; the second IP address is an IP address for communication between arbitrary one of the first nodes and the second nodes; the first nodes communicate with the fourth node using the first IP address assigned thereto; wherein the fourth node is a second gateway server for applying communication control for a security measure to the first nodes; and wherein, in a case where the communication control for the security measure for the first node is performed by the second gateway server, the third node assigns the first IP address with a first netmask having a number of bits smaller than the second netmask to the first nodes the second nodes communicate with arbitrary one of the first nodes using the second IP address assigned thereto.