Patent ID: 7526671

Claim:
A network communication system, comprising: a plurality of internal units; a plurality of internal LANs mutually connecting said internal units, said internal LANs being assigned different IP addresses; and a plurality of control units being respectively connected to said internal LANs, wherein each of said control units includes: an external network port being capable of connecting to an external network; port opening/closing means for selectively setting said control unit in an open state, in which said control unit acts as the unit having a common IP address of said control units with respect to the external network, or in a close state, in which an access to said control unit from the external network is prohibited; means for detecting address duplication between network addresses of the IP addresses, which are respectively assigned to said internal LANs, and a network address assigned to the external network; and means for solving the address duplication, said solving means actuating said port opening/closing means to set said control unit in the close state and changing the network address of said corresponding internal LAN so as to solve the address duplication, and wherein one of said control units is set in the open state, and the rest of said control units is set in the close state.