Abstract:
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.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation Application of U.S. patent application Ser. No. 13/497,781, filed on Mar. 22, 2012, which is based on International Application No. PCT/JP2010/066309 filed on Sep. 21, 2010, and which claims priority from Japanese Patent Application No. 2009-218693 filed on Sep. 24, 2009, the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention is related to an inter-virtual-server communication identifying system, and more particularly, to an inter-virtual-server communication identifying system in case of a communication between a plurality of logical servers operating on physical servers. 
     BACKGROUND ART 
     Generally, a plurality of logical servers operating on physical servers are often configured of virtual machines and so on. Conventionally, there are the following two problems in case of a communication between the logical servers which operating on the physical servers. 
     (1) First Problem 
     The first problem is as follows. There is no case that a protocol header is added as a new identifier to the existing traffic in the existing router and switch, in order to know the communication condition between the logical servers. Therefore, it is difficult for a network manager to grasp in real time, the communication condition on which of routes is used for the communication, how is a communication quality, and where a communication fault has occurred, even if the communication is carried out by using a MAC (Media Access Control) address, an IP (Internet Protocol) address, a VLAN (Virtual Local Area Network) ID (identifier), and so on assigned to the logical server. 
     (2) Second Problem 
     The second problem is as follows. In case of an operation condition under the multi-tenant environment such as a data center, there is a case that the IP addresses overlap in case of the communication between virtual machines in the multi-tenant environment. In such a case, it is impossible to carry out the communication, unless the re-numbering of the IP address or address conversion through NAT (Network Address Translation) is carried out. However, in order to carry out the re-numbering of the IP address, it is required to stop service so that a large load is imposed. It should be noted that it is supposed that NAT contains NAPT (Network Address Port Translation) such as IP masquerade. Also, because NAT is dependent on application, the NAT could not be used unless confirming that application is coordinated. Therefore, there was a case which a problem, had occurred in the communication among the virtual machines under the multi-tenant environment. 
     Regarding (1), in the condition that a protocol header as a new identifier is not added to the existing traffic, the router and switch for relay have not a function of grasping a communication flow condition between the virtual machines. Therefore, it is difficult to grasp a communication path, a communication performance, and a communication fault situation in real time. 
     Regarding (1), there is a VN-Tag technique of Cisco (registered trademark) which can solve the above problems by adding a protocol header as a new identifier to the existing traffic (Non-Patent Literatures 1 and 2). The function of grasping the communication condition is realized in the VN-Tag technique by introducing a special router and switch which can insert the new header into the existing packet is proposed. However, because the new header cannot be grasped by the existing router or switch which cannot grasp the VN-Tag, the communication flow condition between the virtual machines cannot be grasped in the general environment which coexists with the existing network. 
     Therefore, it is required to allow a network manager to grasp the communication flow condition between the virtual machines in real time while keeping backward compatibility in the existing Internet network. 
     Regarding (2), in the multi-tenant environment which provides a server, a storage and network environment for a plurality of enterprises by the data center and so on, there is a case that addresses assigned to the virtual machines overlap. In each company, the address assignment in the intranet is typically implementing by using a space of private IP addresses. 
     It should be noted that the private IP address is an IP address used in the network not connected directly with the Internet (e.g. the in-house network) such as a perfectly closed network which is not connected with an external network (the Internet), and a network connected indirectly with the external network (the Internet) through a router and so on. The private IP address is also referred to as a private address. 
     Even if the addresses are uniquely assigned in the in-house system, there is a case that the addresses overlap between the companies. Therefore, when the IP addresses assigned to virtual machines on a server outsourced to the data center overlap, the inter-virtual-machine communication between companies (multi-tenants) cannot be conventionally carried out unless the address re-numbering and NAT are carried out. However, there is a problem on operation in case of either of the address re-renumbering or the NAT. 
     Therefore, in the multi-tenant network of the data center, it is required that the virtual machine communication between multi-tenants can be carried out even under the environment that the IP addresses of the virtual machines overlap, and a network manager can grasp the communication flow condition in real time. 
     As the related techniques, JP 2008-278478A (Patent Literature 1) discloses a computing system and a communication control method. In this related technique, data showing a pair of a virtual machine and a physical machine on which the virtual machine operates is recorded in a memory shared by the virtual machine and a virtual machine environmental control function. Also, it is determined whether or not a counter-end virtual machine exists on the same physical machine as the virtual machine, based on the above-mentioned recorded data. Also, a multiplicity is changed by the determination. Moreover, when the virtual machine migrates to another physical machine, the above-mentioned recorded data is rewritten. 
     JP 2007-158870A (Patent Literature 2) discloses a virtual computer system and a network communication method. In this related technique, switching is carried out between a VLAN communication according to a VLAN ID set to a virtual network interface card (NIC) and a VLAN communication according to a VLAN ID set by an OS on the virtual machine which uses the virtual network interface card, based on whether or not to the VLAN ID is set to the virtual network interface card. 
     It should be noted that in this related technique, VLAN is realized by using a tag VLAN which is standardized in IEEE 802.1Q. In a communication packet prescribed in IEEE 802.1Q, a VLAN tag field is added to a communication packet which does not contain the VLAN tag (VLAN Tag). The VLAN tag field is composed of a tag type and tag control data, and 12 bits of the tag control data are assigned for the VLAN ID. 
     CITATION LIST 
     
         
         [Patent Literature 1] JP 2008-278478A 
         [Patent Literature 2] JP 2007-158870A 
         [Non-Patent Literature 1] Cisco (registered trademark) VN-Link: Virtualization correspondence networking http://www.cisco.com/web/JP/solution/places/datacenter/literature/white_paper_c11-525307.html 
         [Non-Patent Literature 2] Recognition of virtual machine individually and realization of network which can be cared every virtual machine &lt;http://www.cisco.com/web/JP/news/cisco_news_letter/tech/vnlink/index.html&gt; 
       
    
     SUMMARY OF THE INVENTION 
     A first object of the present invention is to make it possible for a network manager to grasp a communication flow condition between virtual machines in real time while keeping backward compatibility in the existing Internet network. 
     A second object of the present invention is to make it possible for a network manager to grasp a communication flow condition in real time while an inter-multi-tenant communication between virtual machines can be carried out even under the environment that IP addresses of the virtual machines overlap in a multi-tenant network of a data center. 
     An inter-virtual-server communication identifying system of the present invention includes a reception-side physical server, a transmission-side physical server and a physical switch. The reception-side physical server assigns a reception-side virtual machine ID (identifier) to a reception-side virtual server. The transmission-side physical server assigns a transmission-side virtual machine ID to a transmission-side virtual server. Also, the transmission-side physical server assigns the reception-side virtual machine ID and the reception-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 TCP/IP (Transmission Control Protocol/Internet Protocol) packet, when generating the transmission packet from the transmission-side virtual server to the reception-side virtual server, and transmits the transmission packet. The physical switch is provided on a network connecting the transmission-side physical server and the reception-side physical server, and identifies the transmission packet based on the reception-side, virtual machine ID and the reception-side virtual machine ID which are contained in the bit space, when relaying the transmission packet between the transmission-side physical server and the reception-side physical server, and grasps data indicating a network condition. 
     A physical server of the present invention is provided with a virtual server, a virtual switch, and an NIC. The virtual server is assigned with a virtual machine ID (identifier). The virtual switch controls a communication of the virtual server, and outputs a transmission packet in a form of TCP/IP (Transmission Control Protocol/Internet Protocol) packet, in case of a communication between the virtual server and another virtual server through a network. The NIC transmits the transmission packet onto the network. 
     In an inter-virtual-server communication identifying method, a reception-side virtual machine ID (identifier) is assigned to a reception-side virtual server by a reception-side physical server. A transmission-side virtual machine ID is assigned to a transmission-side virtual server by a transmission-side physical server. A transmission packet is transmitted by assigning 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 the transmission packet in a form of TCP/IP (Transmission Control Protocol/Internet Protocol) packet, when generating the transmission packet from the transmission-side virtual server to the reception-side virtual server. The transmission packet is identified based on the reception-side virtual machine ID and the transmission-side virtual machine ID which are contained in the bit space, to collect data indicating a network condition, by a physical switch provided on a network connecting the transmission-side physical server and the reception-side physical server, when relaying the transmission packet between the transmission-side physical server and the reception-side physical server. 
     A program of the present invention is a program to make a computer execute the steps of: controlling a communication of a virtual server assigned with a virtual machine ID (identifier); and, transmitting on a network, a transmission packet which the virtual machine ID is assigned to at least a part of a bit space of a field other than a data field of the transmission packet in a form of TCP/IP (Transmission Control Protocol/Internet Protocol) packet, in case of a communication between the virtual server and another virtual server through the network. 
     The communication flow condition between the virtual machines can be grasped in the network by using a field where the existing router and switch can grasp. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a configuration example of an inter-virtual-server communication identifying system of the present invention; 
         FIG. 2  is a diagram showing a first exemplary embodiment of the present invention; 
         FIG. 3  is a sequence diagram showing a communication flow control in the first exemplary embodiment of the present invention; 
         FIG. 4  is a diagram showing a second exemplary embodiment of the present invention; 
         FIG. 5  is a sequence diagram showing the communication flow control in the second exemplary embodiment of the present invention; 
         FIG. 6  is a diagram showing a third exemplary embodiment of the present invention; 
         FIG. 7  is a sequence diagram showing the communication flow control in the third exemplary embodiment of the present invention; 
         FIG. 8  is a diagram showing a fourth exemplary embodiment of the present invention; 
         FIG. 9  is a sequence diagram showing the communication flow control in the fourth exemplary embodiment of the present invention; 
         FIG. 10  is a diagram showing a configuration example of a data center in multi-tenant environment; 
         FIG. 11  is a diagram showing a fifth exemplary embodiment of the present invention; 
         FIG. 12A  is a sequence diagram showing the communication flow control in the fifth exemplary embodiment of the present invention; 
         FIG. 12B  is a sequence diagram showing the communication flow control in the fifth exemplary embodiment of the present invention; 
         FIG. 13  is a diagram showing a configuration example of the inter-virtual-server communication identifying system of the present invention; and 
         FIG. 14  is a diagram showing a sixth exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention will be described with reference to the attached drawings. 
     As shown in  FIG. 1 , an inter-virtual-server communication identifying system of the present invention is provided with a first physical server  10 , a second physical server  20 , and a network  30 . 
     Here, as an example of the first physical server  10  and the second physical server  20 , computers such as a PC (personal computer), a client server, a work station, a mainframe, and a supercomputer are exemplified. It should be noted that it is sufficient that each of the first physical server  10  and the second physical server  20  is sufficient to be a server which can be connected with the network and can realize the environment under which virtual machines are possible to operate. Therefore, as another example of the first physical server  10  and the second physical server  20 , a mobile terminal, a car navigation system, a home game machine, an interactive TV, a digital tuner, a digital recorder, information home appliance, an OA (Office Automation) equipment and so on are exemplified. Also, the first physical server  10  and the second physical server  20  may be mounted on moving bodies such as a vehicle, a ship, and an aircraft. However, actually, it is not limited to these examples. 
     Also, as an example of the network  30 , the Internet, a LAN (Local Area Network), a wireless LAN, a WAN (Wide Area Network), a backbone, a fixation telephone network, a mobile telephone network, WiMAX (IEEE 802.16a), 3G (3rd Generation), a lease line, a community antenna television (CATV) line, an IrDA (Infrared Data Association), a Bluetooth (registered trademark), a serial communication circuit and so on are exemplified. However, actually, the present invention is not limited to these examples. 
     The first physical server  10  is provided with virtual servers  11  ( 11 - i , i=1 to n: n is an optional natural number), a virtual switch  12 , a NIC (Network Interface Card)  13 , and a communication flow monitoring section  14 . In the same way, the second physical server  20  is provided with virtual servers  21  ( 21 - i , i=1 to n), a virtual switch  22 , a NIC  23  and a communication flow monitoring section  24 . The network  30  contains a physical switch  31  and a physical switch  32 . 
     The virtual servers  11  ( 11 - i , i=1 to n) are virtual machines which operate on the first physical server  10 . In the same way, the virtual servers  21  ( 21 - i , i=1 to n) are virtual machines which operate on the second physical server  20 . Here, as an example of the virtual servers  11  ( 11 - i , i=1 to n), a virtual server “A”  11 - 1 , a virtual server “B”  11 - 2 , and a virtual server “C”  11 - 3  are shown. Also, as an example of the virtual servers  21  ( 21 - i , i=1 to n), the virtual server “D”  21 - 1 , the virtual server “E”  21 - 2  and the virtual server “F”  21 - 3  are shown. It should be noted that actually, the number of virtual servers  21  ( 21 - i , i=1 to n) does not have to be the same as the number of virtual servers  11  ( 11 - i , i=1 to n). 
     The virtual switch  12  carries out a communication control of each of the virtual servers ( 11 - i , i=1 to n) on the first physical server  10 . In the same way, the virtual switch  22  carries out the communication control of each of the virtual servers ( 21 - i , i=2-n) on the second physical server  20 . As an example of each of the virtual switch  12  and the virtual switch  22 , a hypervisor, a virtual machine monitor (VMM) and so on are exemplified. Here, it is assumed that the virtual switch  12  and the virtual switch  22  control the generation, operation, migration, stop and deletion of the virtual servers  11  ( 11 - i , i=1 to n) and the virtual servers  21  ( 21 - i , i=2 to n). However, actually, the present invention is not limited to these examples. 
     The virtual switch  12  is provided with a virtual machine ID assigning section  121 , a MAC address assigning section  122 , and an IP address assigning section  123 . In the same way, the virtual switch  22  is provided with a virtual machine ID assigning section  221 , a MAC address assigning section  222 , and an IP address assigning section  223 . 
     Each of the virtual machine ID assigning section  121  and the virtual machine ID assigning section  221  newly assigns a VLAN ID which the existing router and switch can grasp and identify, as a virtual machine ID (VMid) of a corresponding one of the virtual servers. The virtual machine ID is identification data which is different from a MAC address and an IP address and does not depend on the existing communication protocol. 
     Each of the MAC address assigning section  122  and the MAC address assigning section  222  assigns a MAC address to a corresponding one of the virtual servers. This MAC address is a private MAC address. The private MAC address can be freely set basically. 
     Each of the IP address assigning section  123  and the IP address assigning section  223  assigns an IP address to a corresponding one of the virtual servers. The IP address is a private IP address. The first physical server  10  and the second physical server  20  can know the MAC address of a counter-side virtual server by use of a command of ARP (Address Resolution Protocol) and a table, if the IP address of the counter-side virtual server is known. 
     It should be noted that a case that the plurality of physical servers use a private IP address is thought of. Also, it would be thought of that the virtual machine ID and the MAC address of each virtual server are used as destination data of each virtual server in the physical server, and the IP address assigned to the NIC in the physical server and the IP address of a host are shared. Therefore, there would be a case that the IP addresses of the respective virtual servers overlap. 
     Each of the NIC  13  and the NIC  23  is an extension card for connecting the computer with a LAN (Local Area Network). It should be noted that each of the NIC  13  and the NIC  23  may be a communication interface to connect with an antenna for the radio communication and the network except the LAN. Here, actually, the present invention is not limited to these examples. 
     Here, the NIC  13  is connected with the physical switch  31  in the network  30 . The physical switch  31  in the network  30  is connected with the physical switch  32  in the network  30 . The physical switch  32  in the network  30  is connected with the NIC  23 . Here, as the relay physical switches, two of the physical switches  31  and the physical switches  32  are exemplified. However, actually, the number of physical switches may be one or equal to or more than three. 
     It should be noted that as an example of physical switch  31  and the physical switch  32 , an open flow switch is exemplified. In this case, an open flow controller as a server for controlling the communication flow processing exists together with the open flow switches. The above-mentioned open flow controller is supposed to be contained in the network  30 . Besides, as an example of each of the physical switch  31  and the physical switch  32 , a router, a switching hub, and so on are exemplified. However, actually, the present invention is not limited to these examples. 
     The details of the open flow switch are described in the following literature. “OpenFlow Switch Specification Version 0.9.0 (Wire Protocol 0x98)” (Jul. 20, 2009 Current Maintainer) by Brandon Heller (brandonh@stanford.edu)” &lt;http://www.openflowswitch.org/documents/openflow-spec-v0.9.0.pdf&gt; 
     In case of the reception, each of the communication flow monitoring section  14  and the communication flow monitoring section  24  confirms the virtual machine ID (VMid) contained in the reception packet. 
     The communication flow monitoring section  14  is provided with at least one of a VLAN tag inserting and removing section  141  and a MAC header converting section  142 . Similarly, the communication flow monitoring section  24  is provided with at least one of a VLAN tag inserting and removing section  241  and a MAC header converting section  242 . 
     Each of the VLAN tag inserting and removing section  141  and the VLAN tag inserting and removing section  241  inserts a virtual machine ID (VMid) as a VLAN tag into a transmission packet in case of transmission, and removes the virtual machine ID (VMid) from the reception packet in case of reception. 
     Each of the MAC header converting section  142  and the MAC header converting section  242  converts a part or whole of each of “MAC DA (Destination Address)” and “MAC SA (Source Address)” contained in the MAC-DA/SA field as an MAC header field into a virtual machine ID (VMid) of a virtual server. Here, it is assumed that each of the MAC header converting section  142  and the MAC header converting section  242  converts a part or whole of “MAC DA” into a virtual machine ID (VMid) of a transmission destination virtual server in case of transmission, and converts a part or whole of “MAC SA” into a virtual machine ID (VMid) of a transmission source virtual server. 
     It should be noted that the communication flow monitoring section  14  may be contained in either of the virtual switch  12  or the NIC  13 . In the same way, the communication flow monitoring section  24  may be contained in either of the virtual switch  22  or the NIC  23 . 
     Also, it could be thought of that the communication flow monitoring section  14  is provided between the NIC  13  and the physical switch  31  and the communication flow monitoring section  24  is provided between the NIC  23  and the physical switch  32 . Or, it could be thought of that the communication flow monitoring section  14  is provided in the physical switch  31  (physical switch closest to the first physical server  10 ) directly connected with the NIC  13 , and the communication flow monitoring section  24  is provided in the physical switch  32  (physical switch closest to the second physical server  20 ) directly connected with the NIC  23 . 
     Here, it is supposed that each of the virtual servers  11  ( 11 - i , i=1 to n), the virtual servers  21  ( 21 - i , i=1 to n), the virtual switch  12 , the virtual switch  22 , the communication flow monitoring section  14  and the communication flow monitoring section  24  is realized by a processor driven based on a software program to execute predetermined processing and a memory which stores the program and various data. 
     As an example of the above-mentioned processor, a CPU (Central Processing Unit), a microprocessor, a microcontroller or a semiconductor integrated circuit (Integrated Circuit (IC)) and so on which have a similar function are exemplified. 
     As an example of the above-mentioned memory, semiconductor memory devices such as RAM (Random Access Memory), ROM (Read Only Memory), EEPROM (Electrically Erasable and Programmable Read Only Memory) and flash memory, auxiliary storage units such as HDD (Hard Disk Drive) and SSD (Solid State Drive), and storage media such as DVD (Digital Versatile Disk) and a memory card and so on are exemplified. 
     Also, the above-mentioned memory may be a storage provided in a peripheral device (external HDD, and so on,) and a server (Web server, file server, and so on) in the network, in addition to a storage provided in the computer. Or, the above-mentioned memory may be a storage unit using DAS (Direct Attached Storage), FC-SAN (Fibre Channel-Storage Area Network), NAS (Network Attached Storage), IP-SAN (IP-Storage Area Network), and so on. 
     However, actually, the present invention is not limited to these examples. 
     First Exemplary Embodiment 
     Use of Virtual Machine ID (VMid) for VLAN Tag Stack 
     Referring to  FIG. 2 , a case that the virtual machine ID (VMid) is stacked and used as a VLAN tag will be described. 
     In a first exemplary embodiment of the present invention, the virtual machine ID assigning section newly assigns a VLAN ID which the existing router and switch can grasp and identify, as ID (VMid) of each virtual machine. In case of communication from the virtual server “A” to the virtual server “D”, the communication is carried out by inserting a 2-stage tag of “VMid-A” and “VMid-D” in the packet. That is, th 2-stage tag is two virtual machine IDs (VMid) stacked as the VLAN tag. 
     Specifically, it is as follows. For example, in case of the communication from the virtual server “A” to the virtual server “D”, a transmission packet which contains “MAC DA”-“MAC SA”-“User Data (Data packet)” is transmitted as a TCP/IP (Transmission Control Protocol/Internet Protocol) packet from the physical server on the transmission side, as in ( 1 ) of  FIG. 2 . In this case, the VLAN tag inserting and removing section is provided for either of the virtual switch or the NIC in  FIG. 1 , and a 2-stage tag like ( 2 ) of  FIG. 2  is inserted into the transmission packet by the VLAN tag inserting and removing section in transmission (VLAN tag 2-stage insertion), and the transmission packet is transmitted to the physical switch in the network. 
     The relay physical switch grasps a network condition by monitoring only the VLAN tag field of the TCP/IP packet. That is, the relay physical switch monitors the VLAN tag field of the TCP/IP packet and collects data of the network condition. 
     For example, in the open flow switch, an optional combination of the MAC address field, the VLAN tag field, the IP address field, and the port number field is set as identification data, in the TCP/IP packet and packets which have identical identification data are grasped as the concept of a “flow”. 
     In this case, the relay physical switch monitors only the VLAN tag field of a TCP/IP packet, grasps a packet in which a combination of the virtual machine IDs contained in the VLAN tag field is same, as the same flow, collects data of the network condition from the flow and a destination of this flow, and transmits the collected data to the open flow controller. The open flow controller analyzes and displays the collected data of network condition on the management screen according to the necessity. 
     After removing the 2-stage tag from a reception packet by the VLAN tag inserting and removing section in the NIC or the virtual switch, said reception-side physical server transmits the reception packet to the reception-side virtual server “D”. 
       FIG. 3  is a sequence diagram of a communication flow control in the first exemplary embodiment of the present invention. 
     (1) Step S 101   
     In the first physical server  10  shown in  FIG. 1 , the virtual machine ID assigning section  121  of the virtual switch  12  assigns a virtual machine ID to each of the virtual servers  11  ( 11 - i , i=1 to n). 
     (2) Step S 102   
     Also, the MAC address assigning section  122  of the virtual switch  12  assigns a MAC address to each of the virtual servers  11  ( 11 - i , i=1 to n). 
     (3) Step S 103   
     Also, the IP address assigning section  122  of the virtual switch  12  assigns an IP address to each of the virtual servers  11  ( 11 - i , i=1 to n). 
     (4) Step S 104   
     In the same way, in the second physical server  20 , the virtual machine ID assigning section  221  of the virtual switch  22  assigns a the virtual machine ID to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (5) Step S 105   
     Also, the MAC address assigning section  222  of the virtual switch  22  assigns a MAC address to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (6) Step S 106   
     Also, the IP address assigning section  222  of the virtual switch  22  assigns an IP address to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (7) Step S 107   
     In case of a communication from the virtual server “A”  11 - 1  to the virtual server “D”  21 - 1 , in the first physical server  10 , the transmission-side virtual server “A”  11 - 1  generates a TCP/IP packet which contains “MAC DA”-“MAC SA”-“User Data”, and outputs it to the virtual switch  12  as a transmission packet. It should be noted that actually, in response to a data transmission request from the transmission-side virtual server  11 , the virtual switch  12  may generate a TCP/IP packet every requesting virtual server  11 . 
     (8) Step S 108   
     The communication flow monitoring section  14  confirms the transmission packet from the virtual switch  12 . The VLAN tag inserting and removing section  141  of the communication flow monitoring section  14  inserts a 2-stage tag in the transmission packet and outputs it to the NIC  13 . 
     (9) Step S 109   
     The NIC  13  transmits the transmission packet to the physical switch  31  on the network. 
     (10) Step S 110   
     The physical switch  31  transmits the transmission packet to the physical switch  32 . The physical switch  32  transmits the transmission packet to the reception-side second physical server  20 . At this time, the physical switch  31  and the physical switch  32  grasp a network condition by monitoring the VLAN tag field of the transmission packet. That is, the physical switch  31  and the physical switch  32  monitor the VLAN tag field of the TCP/IP packet and collect data of the network condition. 
     (11) Step S 111   
     In the reception-side second physical server  20 , the NIC  23  receives the transmission packet and outputs it to the communication flow monitoring section  24  as a reception packet. 
     (12) Step S 112   
     The communication flow monitoring section  24  confirms the reception packet which arrives at the NIC  23 . The VLAN tag inserting and removing section  241  of the communication flow monitoring section  24  removes or deletes the 2-stage tag from the reception packet and then outputs the reception packet to the virtual switch  12 . The virtual switch  12  transmits the reception packet to the reception-side virtual server “D”  21 - 1 . 
     Through the above operation, the communication flow condition between the virtual machines can be grasped in the network by use of the field where the existing router and switch can grasp. 
     Second Exemplary Embodiment 
     Conversion of MAC Header into Virtual Machine ID (VMid) 
     Referring to  FIG. 4 , a case that a part or whole of the MAC header is converted into a virtual machine ID (VMid) will be described. Here, a case of an MAC header will be described as an example, but a case of the IP header is similar basically. It is supposed that a MAC header means the MAC address field of the TCP/IP packet and the IP header means the IP address field of the TCP/IP packet. 
     In a second exemplary embodiment of the present invention, the virtual machine ID assigning section assigns an ID (VMid) of each of the virtual machines to a part or whole of the MAC address field which the existing router and switch can grasp and identify. In case of the communication from the virtual server “A” to the virtual server “D”, the communication is carried out by converting parts of “MAC DA” and “MAC SA” of the packet on the way. 
     Specifically, it is as follows. For example, in case of the communication from the virtual server “A” to the virtual server “D”, in the transmission-side physical server, a packet which contains “MAC DA”-“MAC SA”-“User Data” as shown in ( 1 ) of  FIG. 4  is transmitted as the TCP/IP packet. In this case, the MAC header converting section is provided for either of the virtual switch or the NIC. By converting the part or whole of “MAC DA” into the virtual machine ID “VMid-D” of the virtual server “D” by the MAC header converting section in transmission, as shown in ( 2 ) of  FIG. 4 , and by converting a part or whole of “MAC SA” into the virtual machine ID “VMid-A” of the virtual server “A”, the transmission packet is transmitted to the physical switch in the network. 
     The relay physical switch grasps and finds the network condition by monitoring only the MAC-DA/SA field as a MAC header field of the TCP/IP packet. That is, the relay physical switch monitors the MAC header area of the TCP/IP packet and collects data of the network condition. 
     In said reception-side physical server, after converting MAC-DA/SA (parts of “MAC DA” and “MAC SA”) of the reception packet into the original address, the MAC header converting section in the NIC or the virtual switch transmits to the reception-side virtual server “D”. 
       FIG. 5  is a sequence diagram showing the communication flow control in the second exemplary embodiment of the present invention. 
     (1) Step S 201   
     In the first physical server  10  shown in  FIG. 1 , the virtual machine ID assigning section  121  of the virtual switch  12  assigns a virtual machine ID to each of the virtual servers  11  ( 11 - i , i=1 to n). 
     (2) Step S 202   
     Also, the MAC address assigning section  122  of the virtual switch  12  assigns a MAC address to each of the virtual servers  11  ( 11 - i , i=1 to n). 
     (3) Step S 203   
     Also, the IP address assigning section  122  of the virtual switch  12  assigns an IP address to each of the virtual servers  11  ( 11 - 1 , i=1 to n). 
     (4) Step S 204   
     In the same way, in the second physical server  20 , the virtual machine ID assigning section  221  of the virtual switch  22  assigns a virtual machine ID to each of the virtual servers  21  ( 21 - 1 , i=1 to n). 
     (5) Step S 205   
     Also, the MAC address assigning section  222  of the virtual switch  22  assigns a MAC address to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (6) Step S 206   
     Also, the IP address assigning section  222  of the virtual switch  22  assigns an IP address to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (7) Step S 207   
     In case of communication from the virtual server “A”  11 - 1  to the virtual server “D”  21 - 1 , in the first physical server  10  shown in  FIG. 1 , the transmission-side virtual server “A”  11 - 1  generates a TCP/IP packet which contains “MAC DA”-“MAC SA”-“User Data” and outputs it to the virtual switch  12  as the transmission packet. Actually, the virtual switch  12  may generate the TCP/IP packet every requesting virtual server  11  in response to a data transmission request from the transmission-side virtual server  11 . 
     (8) Step S 208   
     The communication flow monitoring section  14  confirms the transmission packet from the virtual switch  12 . The MAC header converting section  142  of the communication flow monitoring section  14  converts a part or whole of “MAC DA” into the virtual machine ID “VMid-D” of the virtual server “D”  21 - 1 , and converts a part or whole of “MAC SA” into the virtual machine ID “VMid-A” of the virtual server “A”  11 - 1 , and outputs the transmission packet after the conversion to the NIC  13 . 
     (9) Step S 209   
     The NIC  13  transmits the transmission packet to the physical switch  31  in the network. 
     (10) Step S 210   
     The physical switch  31  transmits the transmission packet to the physical switch  32 . The physical switch  32  transmits the transmission packet to the reception-side second physical server  20 . At this time, each of the physical switch  31  and the physical switch  32  grasps and finds a network condition by monitoring MAC-DA/SA field which is the MAC header field. That is, the physical switch  31  and the physical switch  32  monitor the MAC-DA/SA field of the TCP/IP packet and collect data of the network condition. 
     (11) Step S 211   
     In the reception-side second physical server  20 , the NIC  23  receives and outputs the transmission packet to the communication flow monitoring section  24  as a reception packet. 
     (12) Step S 212   
     The communication flow monitoring section  24  confirms the reception packet which arrives in the NIC  23 . The MAC header converting section  242  of the communication flow monitoring section  24  converts the MAC-DA/SA field (parts of “MAC DA” and “MAC SA”) of the reception packet into an original condition and outputs the reception packet to the virtual switch  12 . The virtual switch  12  transmits the reception packet to the reception-side virtual server “D”  21 - 1 . 
     Through the above operation, the communication flow condition between the virtual machines can be grasped in the network by using the field called MAC-DA/SA where existing router and switch can grasp and identify. 
     It should be noted that in the present exemplary embodiment, a case where a part or whole of the MAC header is converted into the virtual machine ID (VMid) will be described. However, actually, the part or whole of the IP header may be converted into the virtual machine ID (VMid). That is, a part or whole of at least one of the MAC header and the IP header (both are permitted) may be converted into the virtual machine ID (VMid). 
     At this time, for example, it is technically possible that a part or whole of the transmission-side MAC address field is converted into the transmission-side virtual machine ID (VMid), and a part or whole of the reception-side IP address field is converted into the reception-side virtual machine ID (VMid). Oppositely, it is possible that a part or whole of the transmission-side IP address field is converted into the transmission-side virtual machine ID (VMid) and a part or whole in the reception-side MAC address field is converted into the reception-side virtual machine ID (VMid). 
     Third Exemplary Embodiment 
     Assignment of MAC Address to Virtual Machine ID (VMid) 
     Referring to  FIG. 6 , a case where the virtual machine ID (VMid) is assigned to the MAC address in advance will be described. Here, although the case where the virtual machine ID (VMid) is assigned to the MAC address will be described, a case where the virtual machine ID (VMid) is assigned to the IP address is same basically. 
     In a third exemplary embodiment of the present invention, the virtual machine ID assigning section assigns the ID (VMid) of each virtual machine to a part or whole of the MAC address field which the existing router or switch can grasp and identify. In case of a communication from the virtual server “A” to the virtual server “D”, the packet with “MAC DA” and “MAC SA”, each of which is a MAC address assigned with each virtual machine ID (VMid) is transmitted as just as it is. 
     Specifically, it is as follows. For example, the transmission-side physical server provides the MAC address assigning section for the virtual switch, and the MAC address assigning section assigns the virtual machine ID of the virtual server to a part or whole of the MAC address which is assigned to each of the virtual servers, as in ( 1 ) of  FIG. 6 , in case of assigning an the MAC address to each of the virtual servers. 
     In this example, the MAC address assigning section generates the MAC addresses corresponding to the virtual machine IDs assigned to the virtual servers “A” and the virtual servers “D”, and the generated the MAC addresses are assigned to the virtual servers “A” and the virtual servers “D”, respectively. 
     It should be noted that as for the generated MAC address, there are a case that a part of the MAC address field corresponds to the virtual machine ID and a case that the whole of the MAC address field corresponds to the virtual machine ID. In the case of the communication from the virtual server “A” to the virtual server “D”, the transmission-side virtual server “A” outputs the TCP/IP packet which contains the virtual machine ID, to MAC-DA/SA (parts of “MAC DA” and the “MAC SA”). 
     The relay physical switch grasps a network condition by monitoring only the MAC-DA/SA field contained in the MAC address field of the TCP/IP packet. That is, the relay physical switch monitors the MAC-DA/SA field of the TCP/IP packet and collects data of the network condition. 
     The reception-side physical server transmits the TCP/IP packet to the reception-side virtual server “D”. 
     In the second exemplary embodiment, a part or whole of the MAC address field of the transmission packet is converted into the virtual machine ID in transmission, while in the third exemplary embodiment, the virtual machine ID is incorporated into the MAC address assigned to each of the virtual servers in advance. 
     The MAC address which is assigned to each of the virtual servers is a private MAC address, and the virtual machine ID can be used for a part or whole of the MAC address field because it is basically possible to set freely. 
     For example, generally, the MAC address is configured of a bender ID of upper 3 octets (24 bits: 1 octet=8 bits) and a hardware ID of lower 3 octet (24 bits). 
     Therefore, it is thought of to use a virtual machine ID for a part or whole of the hardware. ID. Or, it is thought of to simply use the virtual machine ID for several bits from the head or end of the MAC address. 
     However, actually, the present invention is not limited to these examples. 
       FIG. 7  is a sequence diagram showing the communication flow control according to the third exemplary embodiment of the present invention. 
     (1) Step S 301   
     At the first physical server  10  shown in  FIG. 1 , the virtual machine ID assigning section  121  of the virtual switch  12  assigns the virtual machine ID to each of the virtual servers  11  ( 11 - 1 , i=1 to n). 
     (2) Step S 302   
     Also, in case of assigning the MAC address to each of the virtual servers  11  ( 11 - i , i=1 to n), the MAC address assigning section  122  of the virtual switch  12  assigns the MAC address using the virtual machine ID “VMid-A” of the virtual server “A”  11 - 1  for a part or whole of the MAC address field of the virtual server “A”  11 - 1 . 
     (3) Step S 303   
     Also, the IP address assigning section  122  of the virtual switch  12  assigns the IP address to each of the virtual servers  11  ( 11 - i , i=1 to n). 
     (4) Step S 304   
     In the same way, in the second physical server  20 , the virtual machine ID assigning section  221  of the virtual switch  22  assigns the virtual machine ID to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (5) Step S 305   
     Also, the MAC address assigning section  222  of the virtual switch  22  assigns the MAC address using the virtual machine ID “VMid-D” of the virtual server “D”  21 - 1  to a part or whole of the MAC address field of the virtual server “D”  21 - 1  in case of assigning the MAC address to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (6) Step S 306   
     Also, the IP address assigning section  222  of the virtual switch  22  assigns the IP address to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (7) Step S 307   
     In case of communication from the virtual server “A”  11 - 1  to the virtual server “D”  21 - 1 , in the first physical server  10 , the transmission-side virtual server “A”  11 - 1  generates the TCP/IP packet containing “MAC DA”-“MAC SA”-“User Data”, and outputs it to the virtual switch  12  as the transmission packet. 
     It should be noted that actually, the virtual switch  12  may generate a TCP/IP packet every requesting virtual server  11  in response to a data transmission request from the transmission-side virtual server  11 . The virtual switch  12  outputs the transmission packet to the NIC  13 . Here, the communication flow monitoring section  14  is not used. 
     (8) Step S 308   
     The NIC  13  transmits the transmission packet to the physical switch  31  in the network. 
     (9) Step S 309   
     The physical switch  31  transmits the transmission packet to the physical switch  32 . The physical switch  32  transmits the transmission packet to the reception-side second physical server  20 . 
     At this time, each of the physical switch  31  and the physical switch  32  grasps a network condition by monitoring the MAC-DA/SA field as an MAC header area of the transmission packet. That is, each of the physical switch  31  and the physical switch  32  monitors the MAC-DA/SA field of the TCP/IP packet and collects data of the network condition. 
     (10) Step S 310   
     In the reception-side second physical server  20 , the NIC  23  receives and outputs the transmission packet to the virtual switch  12  as the reception packet. The virtual switch  12  transmits the reception packet to the reception-side virtual server “D”  21 - 1 . 
     Through the above operation, the communication flow condition between the virtual machines can be grasped in the network by use of the field called MAC-DA/SA where existing router and switch can grasp. 
     It should be noted that in the present exemplary embodiment, a case of assigning the virtual machine ID (VMid) to the MAC address will be described. However, actually, the virtual machine ID (VMid) may be assigned to the IP address. That is, the virtual machine ID (VMid) can be assigned to at least one of the MAC header and the IP header. 
     At this time, it is technically possible to assign the transmission-side virtual machine ID (VMid) to the transmission-side MAC address field and assign the reception-side virtual machine ID (VMid) to the reception-side IP address field. Oppositely, it is possible to assign the transmission-side virtual machine ID (VMid) to the transmission-side IP address field and assign the reception-side virtual machine ID (VMid) to the reception-side MAC address field. 
     Fourth Exemplary Embodiment 
     Assignment of Virtual Machine ID (VMid) to IP+MAC Address 
     Referring to  FIG. 8 , a case of assigning the virtual machine ID (VMid) to each of the MAC address field, the VLAN tag field and the IP address field will be described. 
     In the fourth exemplary embodiment of the present invention, the virtual machine ID assigning section assigns ID (VMid) of each of the virtual machines to a bit space of a part or whole of the MAC address field, a part of whole of the VLAN tag field, and a part of whole of the IP address field which the existing router and switch can grasp and identify, as shown in ( 1 ) of  FIG. 8 . 
     However, actually, there is a case that the VLAN tag field itself does not exist. In case of the communication from the virtual server “A” to the virtual server “D”, the packet with “MAC DA”, “MAC SA”, “VLAN Tag”, “IP DA”, “IP SA” is transmitted. 
     That is, in the present exemplary embodiment, flows are grouped based on a plurality of header fields in such a manner that of the header fields of the flow are grouped such that the field of transmission destination identification data (“MAC DA”, “VLAN Tag”, “IP DA”) indicates the virtual machine ID of the virtual server “D”, and such that the field of transmission source identification data (“MAC SA”, “VLAN Tag”, “IP SA”) indicates the virtual machine ID of the virtual server “A”. 
     Specifically, it is as follows. For example, in case of the communication from the virtual server “A” to the virtual server “D”, the transmission-side physical server transmits as TCP/IP packet, a packet containing a part or whole of the MAC address field, a part or whole of the VLAN tag field, and a part or whole of the IP address field corresponding to the virtual machine ID which is assigned to each of the virtual servers “A” and the virtual servers “D”. 
     The relay physical switch grasps a network condition by monitoring the fields of the transmission destination identification data (“MAC DA”, “VLAN Tag”, “IP DA”) and the transmission source identification data (“MAC SA”, “VLAN Tag”, “IP SA”) in the header field of the flow, that is, a combination of the MAC address field, the VLAN tag field and the IP address field, of the TCP/IP packet. 
     That is, the relay physical switch monitors a combination of the MAC address field, the VLAN tag field and the IP address field of the TCP/IP packet and collects data of the network condition. 
     The reception-side physical server transmits the received packet to the reception-side virtual server “D”. 
     While in the third exemplary embodiment, the virtual machine ID is incorporated into only the MAC address assigned to each of the virtual servers in advance, in the fourth exemplary embodiment, the virtual machine ID is incorporated into only the MAC address and the IP address assigned to each of the virtual servers in advance, and the transmission packet is generated by using the MAC address, the VLAN tag, and the IP address in the transmission. It should be noted that it is possible not to provide the VLAN tag for the transmission packet. 
       FIG. 9  is a sequence diagram showing the communication flow control in the fourth exemplary embodiment of the present invention. 
     (1) Step S 401   
     In the first physical server  10  shown in  FIG. 1 , the virtual machine ID assigning section  121  of the virtual switch  12  assigns the virtual machine ID to each of the virtual servers  11  ( 11 - i , i=1 to n). 
     (2) Step S 402   
     In case of assigning the MAC address to each of the virtual servers  11  ( 11 - i , i=1 to n), the MAC address assigning section  122  of the virtual switch  12  assigns the MAC address using the virtual machine ID “VMid-A” of the virtual server “A”  11 - 1  to a part or whole of the MAC address field of the virtual server “A”  11 - 1 . 
     (3) Step S 403   
     In case of assigning the IP address to each of the virtual servers  11  ( 11 - i , i=1 to n), the IP address assigning section  122  of the virtual switch  12  assigns the IP address using the virtual machine ID “VMid-A” of the virtual server “A”  11 - 1  to a part or whole of the IP address field of the virtual server “A”  11 - 1 . 
     (4) Step S 404   
     In the same way, in the second physical server  20 , the virtual machine ID assigning section  221  of the virtual switch  22  assigns the virtual machine ID to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (5) Step S 405   
     In case of assigning the MAC address to each of the virtual servers  21  ( 21 - i , i=1 to n), the MAC address assigning section  222  of the virtual switch  22  assigns the MAC address using the virtual machine ID “VMid-D” of the virtual server “D”  21 - 1  to a part or whole of the MAC address field of the virtual server “D”  21 - 1 . 
     (6) Step S 406   
     In case of assigning the IP address to each of the virtual servers  21  ( 21 - 1 , i=1 to n), the IP address assigning section  222  of the virtual switch  22  assigns the IP address using the virtual machine ID “VMid-D” of the virtual server “D”  21 - 1  to a part or whole of the IP address field of the virtual server “D”  21 - 1 . 
     (7) Step S 407   
     In case of the communication from the virtual server “A”  11 - 1  to the virtual server “D”  21 - 1 , in the first physical server  10 , the transmission-side virtual server “A”  11 - 1  generates a TCP/IP packet containing “MAC DA”-“MAC SA”-“VLAN Tag”-“VLAN Tag”-“IP DA.”-“IP SA”-“User Data”, and outputs TCP/IP packet to the virtual switch  12  as the transmission packet. 
     It should be noted that actually, the virtual switch  12  may generate TCP/IP packet every requesting virtual server  11  in response to the data transmission request from the transmission-side virtual server  11 . Also, actually, there is a case that the VLAN tag field “VLAN Tag” does not exist. The virtual switch  12  outputs the transmission packet to the NIC  13 . Here, the communication flow monitoring section  14  is not used. 
     (8) Step S 408   
     The NIC  13  transmits the transmission packet to the physical switch  31  to the network. 
     (9) Step S 409   
     The physical switch  31  transmits the transmission packet to the physical switch  32 . The physical switch  32  transmits the transmission packet to the reception-side second physical server  20 . 
     At this time, each of the physical switch  31  and the physical switch  32  grasps the network condition by monitoring a combination of the MAC address field, the VLAN tag field and the IP address field of the transmission packet. That is, each of the physical switch  31  and the physical switch  32  monitors the combination of the MAC address field, the VLAN tag field and the IP address field of the TCP/IP packet and collects data of the network condition. 
     (10) Step S 410   
     In the reception-side second physical server  20 , the NIC  23  receives the transmission packet and outputs it to the virtual switch  12  as the reception packet. The virtual switch  12  transmits the reception packet to the reception-side virtual server “D”  21 - 1 . 
     Through the above operation, the communication flow condition between the virtual machines can be grasped in the network by using the field of the transmission destination identification data (“MAC DA”, “VLAN Tag”, “IP DA”) and the transmission source identification data (“MAC SA”, “VLAN Tag”, “IP SA”) as the header area of the flow, that is, the field where the existing router and switch can grasp and identify. 
     Fifth Exemplary Embodiment 
     Use of Virtual NW ID 
     Referring to  FIG. 10  and  FIG. 11 , a case of using a VPN (Virtual Private Network) ID and the VLAN ID as the ID of a virtual network (NW) will be described. Here, the VPN ID (VPNid) will be described by using it as an example. 
     In  FIG. 10 , in a data center of multi-tenant environment as an example of the use environment of the inter-virtual-server communication identifying system, the environment connected to the data center through a VPN router from a plurality of VPNs is shown. 
     As shown in  FIG. 10 , the inter-virtual-server communication identifying system of the present invention contains the first physical server  10 , the second physical server  20 , the network  30  and a virtual network  40 . 
     The first physical server  10 , the second physical server  20  and the network  30  are basically same as those of shown in  FIG. 1 . Here, the second physical server  20  is a server in the data center of multi-tenant environment. Also, as an example of the virtual servers  21  ( 21 - i , i=1 to n), the virtual server “D 1 ”  21 - 4 , the virtual server “D 2 ”  21 - 5  and the virtual server “D 3 ”  21 - 6  are shown. The virtual server “D 1 ”  21 - 4 , the virtual server “D 2 ”  21 - 5  and the virtual server “D 3 ”  21 - 6  are equivalent respectively to the virtual servers “D”  21 - 1  shown in  FIG. 1 . 
     The virtual network  40  contains a VPN router  41 , a VPN router  42 , a VPN router  43  and a VPN router  44 . 
     The VPN router  41  is connected with the physical switch  32 . The VPN router  42  is connected with a server which is equivalent to the virtual server “D”  21 - 1  shown in  FIG. 1 , of the servers in the data center of multi-tenant environment. Here, the VPN router  42  is connected with the second physical server  20 . The VPN router  43  is connected with a server which is equivalent to the virtual server “E”  21 - 2  shown in  FIG. 1 , of the servers in the data center of multi-tenant environment. The VPN router  44  is connected with a server which is equivalent to the virtual server “F”  21 - 3  shown in  FIG. 1 , of the servers in the data center of multi-tenant environment. 
     In the fifth exemplary embodiment of the present invention, the virtual machine ID is assigned to the MAC address and the IP address in advance by the virtual machine ID assigning section, the MAC address assigning section and the IP address assigning section. 
     Thus, the ID of each of the virtual machines can be assigned to a bit space of a part or whole of the MAC address field, a part or whole of the VLAN tag field, and a part or whole of the IP address field which the existing router and switch can grasp and identify. 
     In case of the communication from the virtual server “A” to the virtual server “D”, a packet assigned with “MAC DA”, “MAC SA”, “VLAN Tag”, “IP DA”, and “IP SA” is transmitted. 
     In other words, in the present exemplary embodiment, a plurality of header fields are grouped by supposing that the transmission destination identification data (“MAC DA”, “VLAN Tag”, “IP DA”) shows the virtual machine ID of the virtual server “D” and the transmission source identification data (“MAC DA”, “VLAN Tag”, “IP DA”) shows the virtual machine ID of the virtual server “A”. However, actually, there is a case that the VLAN tag field “VLAN Tag” does not exist. 
     Under multi-tenant environment, when the virtual server “A” (VMid-A) and the virtual server “B” (VMid-B), which are the virtual servers in the identical server, belong to the different tenants, the communication is possible without address collision, because the communication is carried out in an address space of the plurality of headers even under the situation that the same private IP address is assigned to the virtual server “A” (VMid-A), and the virtual server “B” (VMid-B). 
     Specifically, it is as follows. For example, in case of the communication from the virtual server “A” to the virtual server “D”, the transmission-side physical server transmits as the TCP/IP packet, a packet containing the transmission destination identification data (“MAC DA”, “VLAN Tag”, “IP DA”) and the transmission source identification data (“MAC SA”, “VLAN Tag”, “IP SA”), corresponding to the virtual machine IDs assigned to the virtual server “A” and the virtual server “D”, as shown in ( 1 ) of  FIG. 11 . At this time, the header field is encoded by using a part or whole of the MAC address field, a part or whole of the VLAN tag field, a part or whole of the IP address field for appropriately. 
     The relay physical switch grasps the network condition by monitoring the fields of the transmission destination identification data (“MAC DA”, “VLAN Tag”, “IP DA”) and of the transmission source identification data (“MAC SA”, “VLAN Tag”, “IP SA”) in the header field of the flow of the TCP/IP packets. That is, the relay physical switch monitors a combination of the transmission destination identification data and the transmission source identification data of the TCP/IP packet and collects data of the network condition. 
     Moreover, in the VPN router which accommodates a plurality of VPNs, it is required to identify which of the VPNs connected with users the packet should be transferred. For the identification, the VPN ID (VPNid) is recognized from a whole ID space (“MAC DA”, “VLAN Tag”, “IP DA”), and the destination of the packet is changed in the VPN router. There are a plurality of methods in the transmitting method in the VPN router, but basically, it is the encapsulated packet containing the VPNid. As the transmitting method of a packet, there are a “layer 2 encapsulation method” and a “layer 3 encapsulation method” and so on. 
     In the “layer 2 encapsulation method”, layer 2 packet field (“MAC DA”, “MAC SA”, “VLAN Tag”, “IP DA”, “IP SA”, “User Data”) of the received packet is encapsulated just as it is and the encapsulated packet with the VPNid is transferred. 
     In the “layer 3 encapsulation method”, only IP layer (IP layer) field (“IP DA”, “IP SA”, “User Data”) of the received packet is encapsulated and the encapsulated packet with the VPNid is transferred. 
     The attention points to allow the VMid to be saved in End-to-End in each method will be described below. 
     (a) In case of the layer 2 encapsulation method, because all the fields of (“MAC DA”, “VLAN Tag”, “IP DA”)-(“MAC SA”, “VLAN Tag”, “IP SA”) are preserved and there is the VPNid, there is no problem especially. 
     (b) In case of the layer 3 encapsulation method, the data of the field of (“MAC DA”, “VLAN Tag”, or “MAC SA”, “VLAN Tag”) of the fields of (“MAC DA”, “VLAN Tag”, “IP DA”) (“MAC SA”, “VLAN Tag”, “IP SA”) is degenerated to the VPNid. In case of the layer 3 encapsulation method, End-to-End is dealt with by only the fields of “IP DA” and “IP SA”. 
     The reception-side physical server transmits the reception packet to the reception-side virtual server “D”. 
       FIG. 12A  and  FIG. 12B  are a sequence diagram showing the communication flow control in the fifth exemplary embodiment of the present invention. 
     (1) Step S 501   
     In the first physical server  10  shown in  FIG. 1 , the virtual machine ID assigning section  121  of the virtual switch  12  assigns the virtual machine ID to each of the virtual servers  11  ( 11 - i , i=1 to n). 
     (2) Step S 502   
     The MAC address assigning section  122  of the virtual switch  12  assigns the MAC address using the virtual machine ID “VMid-A” of the virtual server “A”  11 - 1  to a part or whole of the MAC address field of the virtual server “A”  11 - 1 , in case of assigning the MAC address to each of the virtual servers  11  ( 11 - i , i=1 to n). 
     (3) Step S 503   
     The IP address assigning section  122  of the virtual switch  12  assigns the IP address using the virtual machine ID “VMid-A” of the virtual server “A”  11 - 1  to a part or whole of the IP address field of the virtual server “A”  11 - 1  in case of assigning the IP address to each of the virtual servers  11  ( 11 - i , i=1 to n). 
     (4) Step S 504   
     Similarly, in the second physical server  20 , the virtual machine ID assigning section  221  of the virtual switch  22  assigns the virtual machine ID to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (5) Step S 505   
     The MAC address assigning section  222  of also the virtual switch  22  assigns the MAC address using the virtual machine ID “VMid-D” of the virtual server “D”  21 - 1  to a part or whole of the MAC address field of the virtual server “D”  21 - 1  in case of assigning the MAC address to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (6) Step S 506   
     The IP address assigning section  222  of the virtual switch  22  assigns the IP address using the virtual machine ID “VMid-D” of the virtual server “D”  21 - 1  to a part or whole of the IP address field of the virtual server “D”  21 - 1  in case of assigning the IP address to each of the virtual servers  21  ( 21 - i , i=1 to n). 
     (7) Step S 507   
     In the first physical server  10 , the transmission-side virtual server “A”  11 - 1  generates a TCP/IP packet containing “MAC DA”-“MAC SA”-“VLAN Tag”-“VLAN Tag”-“IP DA”-“IP SA”-“User Data” in case of the communication from the virtual server “A”  11 - 1  to the virtual server “D”  21 - 1 , and outputs the TCP/IP packet to the virtual switch  12  as the transmission packet. 
     It should be noted that actually, the virtual switch  12  may generate the TCP/IP packet every requesting virtual server  11  in response to the data transmission request from the transmission-side virtual server  11 . Also, actually, there is a case that the VLAN tag field “VLAN Tag” does not exist. The virtual switch  12  outputs the transmission packet to the NIC  13 . Here, the communication flow monitoring section  14  is not used. 
     (8) Step S 508   
     The NIC  13  transmits the transmission packet to the physical switch  31  in the network. 
     (9) Step S 509   
     The physical switch  31  transmits the transmission packet to the physical switch  32 . The physical switch  32  transmits the transmission packet to the VPN router  41 . 
     At this time, the physical switch  31  and the physical switch  32  grasp the network condition by monitoring the fields of transmission destination identification data (“MAC DA”, “VLAN Tag”, “IP DA”) and the transmission source identification data (“MAC SA”, “VLAN Tag”, “IP SA”) of the transmission packet. That is, the physical switch  31  and the physical switch  32  monitor a combination of the transmission destination identification data and the transmission source identification data of the TCP/IP packet and collect data of the network condition. 
     (10) Step S 510   
     When receiving the transmission packet from the physical switch  32 , the VPN router  41  appropriately uses a part or whole of the MAC address field, a part or whole of the VLAN tag field, and a part or whole of the IP address field of the transmission packet to carry out encoding, and generates the encapsulated packet. Also, the VPN router  41  recognizes the concerned VPNid from the ID space of the above-mentioned fields and determines the encapsulated packet destination. Here, it is supposed that the ID space in the above-mentioned field corresponds to “the VPNid-D”. 
     That is, the VPN router  41  adds “the VPNid-D” to the encapsulated packet and then transfers it to the VPN router  42 . The “layer 2 encapsulation method” and the “layer 3 encapsulation method” which are packet transferring methods as described earlier. The VPN router  42  decodes the encapsulated packet to reproduce it to the transmission packet and transmits the transmission packet to the second physical server  20 . 
     (11) Step S 511   
     In the reception-side second physical server  20 , the NIC  23  receives and outputs the transmission packet to the virtual switch  12  as the reception packet. The virtual switch  12  determines the virtual server as the transmission destination of the reception packet based on the congestion of each of the virtual servers in the second physical server  20 , a port number specified by the reception packet and so on. Here, the virtual switch  12  transmits the reception packet to the virtual server “D 1 ”  21 - 4 . 
     Through the above operation, the communication flow condition between the virtual machines can be grasped in the network by using the fields called (“MAC DA”, “VLAN Tag”, “IP DA”)-(“MAC SA”, “VLAN Tag”, “IP SA”) which the existing router and switch can be grasp. Also, in the VPN router, the communication relation of the virtual machine can be maintained in End-to-End after the appropriate conversion. 
     Sixth Exemplary Embodiment 
     Use of Group ID 
     Referring to  FIG. 13 , a case where the virtual servers are virtually grouped into groups such as VLAN and it is made possible to communicate only between the virtual servers of the identical group will be described. 
     As shown in  FIG. 13 , the inter-virtual-server communication identifying system of the present invention is provided with the first physical server  10 , the second physical server  20 , the network  30  and the virtual network  40 . 
     The first physical server  10 , the second physical server  20  and the network  30  are basically the same as those shown in  FIG. 1 . 
     In the present exemplary embodiment, the virtual switch  12  is provided with a group assigning section  124  in addition to the virtual machine ID assigning section  121 , the MAC address assigning section  122 , and the IP address assigning section  123 . Moreover, in the same way, the virtual switch  22  is provided with a group assigning section  224  in addition to the virtual machine ID assigning section  221 , the MAC address assigning section  222 , and the IP address assigning section  223 . 
     The virtual machine ID assigning section  121 , the MAC address assigning section  122 , and the IP address assigning section  123 , the virtual machine ID assigning section  221 , the MAC address assigning section  222  and the IP address assigning section  223  are basically the same as those shown in  FIG. 1 . 
     The group assigning section  124  assigns a group ID to each of the virtual servers  11  ( 11 - i , i=1 to n) to show the VLAN group to which the virtual server  11  ( 11 - i , i=1 to n) belongs. In the same way, the group assigning section  224  assigns a group ID to each of the virtual servers  21  ( 21 - i , i=1 to n) to show the VLAN group to which the virtual server  21  ( 21 - i , i=1 to n) belongs. Here, the VLAN ID is assumed as the group ID. 
     It should be noted that it is supposed that the MAC address, the IP address, and the group ID are assigned to each of virtual server  11  ( 11 - i , i=1 to n) in advance. In the other exemplary embodiments, the same can be applied. 
     In  FIG. 13 , it is supposed that the group ID of a first VLAN group is “GP- 1 ”, and the group ID of a second VLAN group is “GP- 2 ”. 
     It is supposed that the virtual server “A”  11 - 1 , the virtual server “B”  11 - 2 , the virtual server “D”  21 - 1 , the virtual server “E”  21 - 2  belong to a first VLAN group “GP- 1 ”. 
     Also, it is supposed that the virtual server “C”  11 - 3  and the virtual server “F”  21 - 3  belong to a second VLAN group “GP- 2 ”. 
     At this time, it is possible for the virtual server “A”  11 - 1 , the virtual server “B”  11 - 2 , the virtual server “D”  21 - 1  and the virtual server “E”  21 - 2  to communicate to each other. However, the virtual server “C”  11 - 3  and the virtual server “F”  21 - 3  can not communicate because the VLAN groups are different. 
     Referring to  FIG. 14 , a case where the group ID (VLAN ID) is contained in the packet will be described. 
     The group ID is assigned to the VLAN tag field by the virtual server when the transmission packet is transmitted onto the network. 
     The allocation of the virtual machine ID to the transmission packet follows the other exemplary embodiments. In this case, it is supposed that the virtual machine ID (destination ID) of the transmission destination virtual server and the virtual machine ID (Source ID) of the transmission source virtual server are assigned to at least one field of the MAC address field, the VLAN tag field, and the IP address field. It should be noted that although it is desirable that these virtual machine IDs are assigned to the identical field, they may be assigned to the fields which are different. 
     &lt;Relation of Exemplary Embodiments&gt; 
     It should be noted that the above-mentioned exemplary embodiments may be implemented by combining them. 
     (Generalization) 
     As mentioned above, the present invention has a feature that in the inter-virtual-server communication identifying system between a plurality of logical servers operating on physical servers, a mechanism is provided to grasp the communication setting in End-to-End between the logical servers, the communication identifying, the performance monitoring, the End-to-End failure diagnostic, and so on. 
     In the present invention, the following advantages are attained. 
     The first effect is in that the communication condition between the virtual machines can be grasped in the environment that contains the existing switch and router, because the header field of a conventional packet is used to encode the ID space of the virtual machine. 
     The second effect is in that the communication condition between the virtual machines can be grasped in the environment that contains the existing switch and router, because the plurality of fields of the conventional packet header are recognized as the ID space of the virtual machine. 
     The third effect is in that it is possible to carry out a communication even if the IP addresses assigned to the virtual machines in a multi-tenant environment are same, because the plurality of fields of the conventional packet header are recognized as the ID space of the virtual machine. 
     (Supplementary Note) 
     It is possible to describe a part or whole of the above-mentioned exemplary embodiments as the following supplementary notes. However, the present invention is not limited to the following examples. 
     (Supplementary Note 1) 
     A storage medium which stores a program to make a computer execute the steps of: 
     controlling a communication of a virtual server assigned with a virtual machine ID (identifier); and 
     transmitting on a network, a transmission packet which the virtual machine ID is assigned to at least a part of a bit space of a field other than a data field of the transmission packet in a form of TCP/IP (Transmission Control Protocol/Internet Protocol) packet, in case of a communication between the virtual server and another virtual server through the network. 
     (Supplementary Note 2) 
     The storage medium according to supplementary note 1, which stores a program to make a computer execute the steps of: 
     inserting a VLAN tag field which contains the virtual machine ID into the transmission packet when transmitting the transmission packet onto the network; and 
     removing the VLAN tag field of a reception packet from the network to transmit to the virtual server. 
     (Supplementary Note 3) 
     The storage medium according to supplementary note 1 or 2, which stores a program to make the computer further execute the step of: 
     converting at least a part of an address field in a header field of the transmission packet which changes into the virtual machine ID, when transmitting the transmission packet onto the network. 
     (Supplementary Note 4) 
     The storage medium according to any of supplementary notes 1 to 3, which stores a program to make a computer further execute the steps of: 
     incorporating the reception-side virtual machine ID into at least one of the MAC address and the IP address and assigning the MAC address and the IP address to the virtual server, and 
     assigning the MAC address to a MAC address field of the transmission packet and the IP address to an IP address field in the transmission packet, when generating the transmission packet. 
     (Supplementary Note 5) 
     The storage medium according to supplementary note 4, which stores a program to make a computer further execute the step of: 
     assigning said virtual machine ID to the virtual server; and 
     further assigning the virtual machine ID to the VLAN tag field of the transmission packet, when generating the transmission packet. 
     (Supplementary Note 6) 
     The storage medium according to any of supplementary notes 1 to 5, which stores a program to make a computer further execute the steps of: 
     assigning the VLAN ID to said virtual server as a group ID, 
     assigning the VLAN ID to the VLAN tag field of the transmission packet, when the VLAN ID assigned to said virtual server as the group ID is same as the VLAN ID assigned to said reception-side virtual server as the group ID. 
     The exemplary embodiments of the present invention have been described. However, the present invention is not limited to the above-mentioned exemplary embodiments and various modifications are contained in the present invention in a range not deviating from the spirit of the present invention. 
     It should be noted that Insisting on the priority which is based on Japan application number 2009-218693 by this application and elucidation contents about Japan application number 2009-218693 are incorporated into this application by the quotation.