1. An inter-virtual-server communication identifying system comprising: a reception-side physical server configured to assign a reception-side virtual machine ID (identifier) to a reception-side virtual server; a transmission-side physical server configured to assign a transmission-side virtual machine ID to a transmission-side virtual server, assign the reception-side virtual machine ID and the transmission-side virtual machine ID to at least a part of a bit space of a field other than a data field of a transmission packet in a form of a TCP/IP (Transmission Control Protocol/Internet Protocol) packet, when generating the transmission packet from said transmission-side virtual server to said reception-side virtual server, and transmit the transmission packet; and a physical switch provided on a network connecting said transmission-side physical server and said reception-side physical server, and configured to identify the transmission packet based on the reception-side virtual machine ID and the transmission-side virtual machine ID which are contained in the bit space, when relaying the transmission packet between said transmission-side physical server and said reception-side physical server, and collect data indicating a network condition.