NETWORK MANAGEMENT SYSTEM, AND NETWORK DEVICE

There are provided a virtual network management system and a network device that can identify the topology of a virtual network, estimate a virtual network to which various computing devices belong and the locations of the computing devices, and present the virtual network and the locations to a network administrator. In a network management device, the configurations of packet transmission devices and a MAC learning table are managed. A virtual network to which given virtual computing units are connected is identified from information about a virtual packet transmission device identifier, a VLAN identifier, a MAC address, and a packet transmission port number acquired from the MAC learning table. The locations of the virtual computing units in the virtual network are estimated, and the topology is drawn on the screen of a display.