Abstract: In order to make it unnecessary for a user application program to be aware of any redundant configuration even if such a configuration is applied when communication stations, which communicate with each other according to the TCP/IP protocols over the Ethernet, a communication control system is provided wherein a redundancy control device converts a receiver MAC address included in a transmission request into an MAC address of a network adapter to communicate with, when the redundancy control device receives a transmission request from a communication control device, and converts a sender MAC address included in a received frame into the MAC address, which the communication control device of the location communication station is aware of, when the redundancy control device receives the frame from a network adapter.