A system includes a communication control device, a first communication device and a second communication device. The communication control device acquires first network information that identifies a first internal network to which the first communication device is connected, and second network information that identifies a second internal network. The communication control device decides a first method based on the acquired information. The first method indicates a method of transmission from the first communication device to the second communication device, and of transmission from the second communication device to the first communication device. The communication control device transmits information indicating the first method to the first communication device and the second communication device. The first communication device and the second communication device mutually communicate using the first method, based on the received information indicating the first method.