A data generating device is installed more upstream than a switching device for switching based on data of a first layer. The data generating device reads forward management information relating to a forwarding process of forward data from data of a second layer higher than the first layer, determines one or more clients corresponding to destinations of the forward data on the basis of the forward management information, and generates the same number of pieces of transmission data as the number of identified clients, and forwards each of the pieces of transmission data to the switching device in order to transmit the transmission data to each of the clients.