A control server is connected to a plurality of physical nodes that keep control information defining an operation to be taken in accordance with input/output packet characteristics and process the input/output packets according to the control information. The control server includes a first storage unit that stores configuration information about a virtual network configured to include virtual nodes that are virtualized versions of the physical nodes, and a second storage unit that stores virtual network identifying information identifying the virtual network from characteristics of an input packet, and the control server identifies a physical node that configures a virtual network that handles a packet having a characteristic in common with the packet received by the physical node based on a request from the physical node and updates control information for each physical node.