A server, including a virtual machine identifier assigning section to assign an identifier of a virtual machine operating on the server; and a network interface to transmit a packet including a Layer 2 header information which includes the identifier of the virtual machine, wherein the network interface transmits the packet to a packet encapsulate section which encapsulates a packet field including the Layer 2 header information with a virtual network identifier, wherein the virtual network identifier represents a virtual tenant network corresponding to the virtual machine in multiple tenants network.