Communication control method and system

A communication control system which controls packet exchange between a plurality of closed networks and physically one shared server, where server addresses unique to the respective closed networks are assigned to the shared server, comprising:

• a switch having a plurality of physical ports to be connected to the respective closed networks and a gateway side port;
• and
• a gateway connected between the switch and the shared server, wherein
• the switch includes:
• means for attaching an ID tag unique to each physical port to a packet input from each physical port and outputting it from the gateway side port;
• and means for outputting the packet input from the gateway side port, from the physical port corresponding to the ID tag attached to the packet, and
• the gateway includes:
• a conversion table for managing correspondences between ID tags and server addresses;
• means for detecting an ID tag attached to a packet addressed to the gateway received from the switch;
• a first searching means for searching for a server address corresponding to the detected ID tag from the conversion table;
• a first packet modifying means for modifying a destination address of the packet into the searched server address;
• a second searching means for searching for an ID tag corresponding to a source address of a packet addressed to a closed network received from a shared server from the conversion table;
• and
• a second packet modifying means for attaching the searched ID tag to the packet received from the shared server and modifying the source address into a gateway address.