To provide a relay apparatus, communication system and communication program in which communication is made mutually between networks by connecting the same network address networks with each other.

A relay apparatus connects a network A and a network B, whose address system is equal, via a communication line and stores information capable of identifying a transmission direction of communication data in a routing table that an edge router provided in an edge portion of each network stores. The communication data are transferred to a gateway indicated as a transfer destination with respect to the information of the transmission direction.

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