Patent Publication Number: US-11381455-B2

Title: Information system, control server, virtual network management method, and program

Description:
This application is a continuation of U.S. patent application Ser. No. 14/825,406, filed Aug. 13, 2015, which is a continuation of U.S. patent application Ser. No. 13/500,564, filed Apr. 5, 2012, which is a National Stage entry of PCT/JP2010/067640, which was filed on Oct. 7, 2010, which claims priority to Japanese Patent Application No. JP 2009-233895. The entire contents of the above-referenced applications are expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     Reference to Related Application 
     The present invention is based upon and claims the benefit of the priority of Japanese patent application No. 2009-233895 filed on Oct. 7, 2009, the disclosure of which is incorporated herein in its entirety by reference thereto. 
     The present invention relates to an information system, control server, virtual network management method, and program, and particularly to an information system, control server, virtual network management method, and program providing a virtual network. 
     Background of the Invention 
     Patent Document 1 discloses a virtual network constructing device that realizes end-to-end security for each service, security between services at a client, and scalability for a large-scale system. According to this document, when a client selects an available service in launcher software transmitted from a path control server after the client&#39;s authentication request has been accepted, a corresponding path constructing request is transmitted to the path control server. The path control server issues the client an instruction for connecting to a base router, and also issues the base router an instruction for connecting to the client. The document recites that an in-base VLAN can be dynamically constructed between the client and the base router as a result. 
     Patent Document 2 discloses a system for managing customers in a hierarchical manner. Further, Patent Document 3 discloses a peer-to-peer network capable of providing a new network topology. 
     Non-Patent Document 1 proposes a technology called OpenFlow. OpenFlow treats communication as art end-to-end flow, and performs path control, failure recovery, load balancing, and optimization for each flow. An OpenFlow switch that functions as a forwarding node operates according to a flow table appended or updated by an OpenFlow controller according to OpenFlow protocol. In the flow table, pairs of a packet matching rule that specify a packet and an action such as outputting the packet to a specific port, discarding it, or rewriting a header are registered as flow entries. When there is a corresponding entry, the OpenFlow switch processes a received packet according to an action written in the entry, and notifies the OpenFlow protocol of the reception of the packet when there is no corresponding entry. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         [Patent Document 1] Japanese Patent Kokai Publication No. JP-P2009-135805A 
         [Patent Document 2] Japanese Patent Kohyo Publication No. JP-P2007-525728A 
         [Parent Document 3] Japanese Patent Kokai Publication No. JP-P2008-306725A 
         [Non-Patent Document 1] McKeown, Nick et al., “OpenFlow: Enabling Innovation in Campus Networks,” [online], [searched on Jul. 17, 2009], Internet&lt;URL: http://www.openflowswitch.org//docurments/openflow-wp-latest.pdf&gt; 
       
    
     SUMMARY OF THE DISCLOSURE 
     Problems to be Solved by the Invention 
     The entire disclosures of Patent Documents 1 to 3 and Non-Patent Document 1 are incorporated herein in their entirety by reference thereto. 
     The following analysis is given by the present invention. 
     The technologies of Patent Documents 1 to 3 logically divide a network, however, they do not perform detailed path control by determining a policy for each flow. Further, a method such as source routing can be used to perform path control, but the net data amount a packet can contain gets reduced in this case. 
     Regarding this point, Non-Patent Document 1 proposes a configuration in which path control is performed by the OpenFlow switch operating based on the flow table that defines an action for each flow, but the document only discusses network management, access control, and construction of a virtual network by virtualizing the OpenFlow switch as concrete examples of applications of this configuration. 
     The present invention has been made in considering the above circumstances, and it is an object thereof to provide a configuration capable of configuring a virtual network by virtualizing a physical network and achieving finely tuned path control in the virtual network. 
     Mean to Solve the Problems 
     According to a first aspect of the present invention, there is provided an information system, comprising: a plurality of physical nodes that hold control information defining an operation corresponding to the characteristics of an input/output packet(s) and that perform processing on an input/output packet(s) according to the control information; a first storage unit that stores configuration information of a virtual network including a virtual node configured using at least one of the physical nodes; a second storage unit that stores virtual network identifying information identifying the virtual network from characteristics of an input packet; and a control server that identifies a physical node configuring a virtual network that handles a packet having a characteristic in common with a packet received by the physical node based on a request from she physical node and that updates control information for each of the physical nodes. 
     According to a second aspect of the present invention, there is provided a control server, connected to a plurality of physical nodes that hold control information defining an operation corresponding to characteristics of an input/output packet(s) and that perform processing on an input/output packet(s) according to the control information, comprising: a first storage unit, that stores configuration information of a virtual network including a virtual node configured using at least one of the physical nodes; a second storage unit that stores virtual network identifying information identifying the virtual network from characteristics of an input packet; and a control unit that identifies a physical node(s) configuring a virtual network that handles a packet having a characteristic in common with a packet received by the physical node based on a request from the physical node and that updates control information for each of the physical nodes. 
     According to a third aspect of the present invention, there is provided a virtual network management method executed by a control server connected to a plurality of physical nodes that hold control information defining an operation corresponding to characteristics of an input/output packet(s) and that perform processing on an input/output packet(s) according to the control information. The virtual network management method comprises a step of having the control server identify a physical node(s) configuring a virtual network that handles a packet having a characteristic in common with a packet received by the physical node(s) based on a request from the physical node(s) by referring to a first storage unit that stores configuration information of a virtual network including a virtual node configured using at least one of the physical nodes and to a second storage unit that stores virtual network identifying information identifying the virtual network from the characteristics of an input packet; and a step of updating control information for each of the identified physical nodes. This method is tied to the control server, a specific machine connected to the physical nodes and updating the control information thereof. 
     According to a fourth aspect of the present invention, there is provided a program, executed by a computer configuring a control server connected to a plurality of physical nodes that hold control information defining an operation corresponding to characteristics of an input/output packet(s) and that perform processing on an input/output packet(s) according to the control information, having the computer execute a process of having the control server identify a physical node(s) configuring a virtual network that handles a packet having a characteristic in common with a packet received by the physical node(s) based on a request from the physical node(s) by referring to a first storage unit that stores configuration information of a virtual network including a virtual node(s) configured using at least one of the physical nodes and to a second storage unit that stores virtual network identifying information identifying the virtual network from the characteristics of an input packet; and a process of updating control information for each of the identified physical nodes. Note that this program may be stored in a storage medium readable by a computer. In other words, the present invention can be embodied as a computer program product. 
     Effect of the Invention 
     According to the present invention, it becomes possible to perform path control according to the characteristics of a packet on a configured virtual network. Further, high-speed processing can be achieved since no inquiry to the control server is necessary after the control information has been updated and each physical node does not have to refer to a routing table. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing for explaining an outline of the present invention. 
         FIG. 2  is a drawing showing the configuration of a first exemplary embodiment of the present invention. 
         FIG. 3  is a drawing showing a detailed configuration of a physical node of the first exemplary embodiment of the present invention. 
         FIG. 4  is a drawing showing a detailed configuration of a control server of the first exemplary embodiment of the present invention. 
         FIG. 5  is a drawing showing the configuration of a virtual network constructed by the control server of the first exemplary embodiment of the present invention. 
         FIG. 6  is an example of a virtual node table held by the control server of the first exemplary embodiment of the present invention. 
         FIG. 7  is an example of setting information of a virtual node held by the control server of the first exemplary embodiment of the present invention. 
         FIG. 8  is an example of virtual network configuration information held by the control server of the first exemplary embodiment of the present invention. 
         FIG. 9  is a schematic diagram of a virtual network corresponding to the virtual network configuration information in  FIG. 8 . 
         FIG. 10  is an example of virtual network identifying information held by the control server of the first exemplary embodiment of the present invention. 
         FIG. 11  is an example of management switch information held by the control server of the first exemplary embodiment of the present invention. 
         FIG. 12  is an example of a flow entry held by the control server of the first exemplary embodiment of the present invention. 
         FIG. 13  is a drawing showing a correspondence relation between the configuration in  FIG. 2  and the virtual network in  FIG. 5 . 
         FIG. 14  is a sequence diagram for explaining the operation of the first exemplary embodiment of the present invention. 
         FIG. 15  is a sequence diagram for explaining the operation of the first exemplary embodiment of the present invention. 
         FIG. 16  is a sequence diagram for explaining the operation of the first exemplary embodiment of the present invention. 
         FIG. 17  is a sequence diagram for explaining the operation of the first exemplary embodiment of the present invention. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     First, an outline of the present invention will be given with reference to the drawings. As shown in  FIG. 1 , the present invention can be realized by a plurality of physical nodes  10  that hold control information defining actions according to characteristics of input/output packet(s) and that process the input/output packets according to the control information and a control server  20  that comprises a function of updating the control information of the physical nodes  10 . 
     The control sever  20  comprises a first storage unit (virtual network configuration information storage unit)  202  that stores configuration information of a virtual network comprised of virtual nodes which are virtualized versions of the physical nodes  10 ; a second storage unit (virtual network identifying information storage unit)  203  that stores virtual network identifying information that identifies the virtual network from the characteristics of the input packet(s); and a control unit  210  that identifies a physical node(s) configuring a virtual network that handles a packet(s) having a characteristic in common with the packet(s) received by the physical node(s) and that updates control information for each of physical nodes  10  based on a request from the physical node  10  concerned. 
     The physical node  10  can be realized by a switch equivalent to the OpenFlow switch of Non-Patent Document 1 that operates according to the flow table or a router, and notifies the control server  20  that a packet not in the flow table is received upon reception of the packet (request for creating a flow entry; an arrow from the physical node  10  to the control unit  210  in  FIG. 1 ). 
     Upon receiving the request for creating a flow entry, the control server  20  refers to the second storage unit  203  and identifies a virtual network to which the packet concerned should belong from the characteristics (port number, physical node ID, and header information) of the input packet. Next, the control server  20  refers to the first storage unit  202 , suitably performs forwarding processing on the received packet within the virtual network, identifies a physical node or nodes corresponding to the identified virtual network, and updates the control information of the identified physical node or nodes (arrows from the control unit  210  to the physical nodes  10  in  FIG. 1 ). As described, subsequent packets are successively forwarded by the physical nodes according to the control information updated for each virtual network. 
     Further, the control server  20  can be realized by adding the functions relating to the virtual network described above to the OpenFlow controller of Non-Patent Document 1 as a base. Or it is also possible to realize the control server  20  by having another server that provides the functions relating to the virtual network described above work together with the OpenFlow controller of Non-Patent Document 1. 
     First Exemplary Embodiment 
     Next, a first exemplary embodiment of the present invention will be described in detail with reference to the drawings.  FIG. 2  is a drawing showing the configuration of the first exemplary embodiment of the present invention. With reference to  FIG. 2 , a plurality of physical nodes  10 , the control server  20 , and external nodes  30  are shown. 
     The physical nodes  10  are connected each other and it is configured by a switch or router that forwards a packet(s) sent/received to/from the external network  30 . In the present exemplary embodiment, the physical node  10  is assumed to be an OpenFlow switch. 
     The control server  20  is connected to the physical nodes  10  via secure channels and instructs the physical nodes  10  to update the control information. In the present exemplary embodiment, the control server  20  is assumed to be a server that comprises a function as the OpenFlow controller communicating with the physical nodes  10  using the OpenFlow protocol. 
     The external node(s)  30  is configured by a server(s) that provides various services to a user terminal accessing from the external network. In the present exemplary embodiment, the external node  30  is assumed to be an Http (Hyper-Text Transfer Protocol) server. 
       FIG. 3  is a drawing showing a detailed configuration of the physical node of the first exemplary embodiment of the present invention. With reference to  FIG. 3 , the physical node comprises a server communication unit  11  that communicates with the control server  20 , a flow table  12 , and a control unit  13 . According to an instruction from the control server  20 , the control unit  13  adds a new entry to the flow table  12 , searches for an entry having a matching key that matches a received packet in the flow table  12 , and executes a corresponding action. 
       FIG. 4  is a drawing showing a detailed configuration of the control server of the first exemplary embodiment of the present invention. With reference to  FIG. 4 , the control server  20  comprises a virtual node emulation unit  211 , a virtual network control unit  212 , a path control unit  213 , an OpenFlow protocol processing unit  214 , and a storage device that functions as a storage unit storing information discussed later. 
     In the example in  FIG. 4 , the control server  40  comprises a virtual node object storage unit  201 , the virtual network configuration information storage unit  202 , the virtual network identifying information storage unit  203 , a physical topology information storage unit  204 , a shortest path information storage unit  205 , a set flow forwarding path information storage unit  206 , a flow entry storage unit  207 , and a management switch information storage unit  208  configured by the aforementioned storage device. 
     In the explanation below, it is assumed that the control server  20  constructs a virtual network configured by a layer 3 switch (L3SW), a firewall (FW), a load balancer (LB), and a layer 2 switch (L2SW) shown in  FIG. 5 . 
     The virtual node emulation unit  211  performs processing as a virtual node using virtual objects having a class corresponding to the aforementioned L3SW, FW, LB, and L2SW stored in the virtual node object storage unit  201 . For instance, each virtual object is identified by a virtual node table shown in  FIG. 6  in which a virtual node ID on the virtual network is associated with an object ID. 
       FIG. 7  shows an example of setting information of a virtual router object stored in the virtual node object storage unit  201 . The basic operation is the same as a normal physical router device. A destination is determined by referring to a routing table, and a MAC address is resolved by an ARP (Address Resolution Protocol) table and converted into a MAC address of a router of the source MAC address. What is different from a router device on a real network is that a virtual interface ID is stored in the routing table and the virtual interface ID is resolved as the destination. Therefore, upon receiving a packet specifying the virtual router as a virtual node ID from the virtual network control unit  212 , the virtual node emulation unit  211  performs processing as a router on the virtual network and outputs a converted packet of a virtual interface ID and destination MAC address. 
     The setting of the virtual node shown in  FIG. 7  can be changed by a user authorized to use the virtual network. Meanwhile, an association between the physical node and the virtual network discussed later is hidden from the user, and he can utilize the virtual node on the virtual network in the same way as a physical node. 
     The virtual network control unit  212  performs input/output of packet information from/to the virtual node emulation unit  211  according to an association between the configuration information of the virtual network stored in the virtual network configuration information storage unit  202  and the virtual network identifying information storage unit  203  and the real network thereof. Further, the virtual network control unit  212  temporarily stores the received packet in a packet cache  215  and creates conversion contents of a packet header to be instructed to a physical node to which the packet is ultimately outputted. 
       FIG. 8  shows an example of the virtual network configuration information stored in the virtual network configuration information storage unit  202 . It is indicated that a virtual interface of a virtual node indicated in a KEY field is connected by a virtual interface of a virtual node in a Value field. In the example of  FIG. 8 , the virtual node of ID # 1  is connected to the virtual node of ID # 2  by a virtual interface of virtual interface ID # 10 , and the virtual node of ID # 2  is connected to an external node by a virtual interface of virtual interface ID # 30 .  FIG. 9  is a schematic diagram of a virtual network corresponding to the virtual network configuration information in  FIG. 8 . Based on the virtual network configuration information, the virtual network control unit  212  is able to specify a virtual node ID to the virtual node emulation unit  211 , receive a packet, and obtain the results thereof. 
       FIG. 10  shows an example of the virtual network identifying information indicating an association between the virtual network and characteristics of a packet stored in the virtual network identifying information storage unit  203 . In the example of  FIG. 10 , there is an configuration in which for packet matching conditions indicated in a KEY field, a virtual network to which it should belong, the virtual node ID, and the virtual interface can be uniquely determined. Further, by performing a reverse lookup on the table shown in  FIG. 10 , a physical switch ID, physical port ID, vlan-tag on a real network to which a packet having a certain virtual network, virtual node ID, and virtual interface can be determined. The conversion operation between the virtual network and the real network described above is called “physical-virtual conversion” hereinafter in the present description. Further, physical node ID, physical port ID, and header information (source MAC address (mac(src)), destination MAC address (mac(dst)), VLAN number (vlan-tag), source IP address (ip(src)), destination IP address (ip(dst)), source layer 4 port number (14port(src)), and destination layer 4 port number (14port(dst)) are shown in the example of  FIG. 10 , but it is not necessary to use all these pieces of information and it may be configured so that other pieces of header information or packet information can be specified as necessary. 
     By providing as many the tables shown in  FIG. 8  as the number of virtual networks, a plurality of virtual networks can be constructed. Then, by defining packet characteristics for each user and a virtual network that the user is authorized to use using a table as the one shown in  FIG. 9  [sic.  FIG. 10 ], a virtual network can be provided to a plurality of users in a form that the network is logically divided. 
     The virtual network control unit  212  supplies an input packet(s) to the virtual node emulation unit  211 , obtains the processing result thereof, and then supplies a physical node that has received this packet and the port number thereof, and a physical node after physical-virtual conversion performed on the packet on which network processing has been performed by the virtual node emulation unit  211 , and the output port number thereof, to the path control unit  213 . 
     The path control unit  213  calculates a forwarding path for outputting the packet supplied to the physical node based on physical network topology information stored in the physical topology information storage unit  204  from the physical node after the physical-virtual conversion. For this path calculation, for instance, Dijkstra&#39;s shortest path algorithm can be used. 
     Further, the path control unit  213  stores the result of the path calculation in the shortest path information storage unit  205  as a cache for a predetermined period of time. When performing subsequent path calculations, the path control unit  213  refers to the shortest path stored in the shortest path information storage unit  205  and is able to omit the path calculation processing if the cache remains. 
     Further, the path control unit  213  stores a pair of the flow and the shortest path information in the set flow forwarding path information storage unit  206  as well. When performing subsequent path calculations, the path control unit  213  is able to use the path information stored in the set flow forwarding path information storage unit  206 . 
     The shortest path information storage unit  205  and the set flow forwarding path information storage unit  206  can be omitted. Further, how much is stored in each path information can be suitably changed according to the purpose and the hardware specifications of this system. 
     The OpenFlow protocol processing unit  214  instructs each physical node  10  to update the flow table  12  according to the path information calculated by the path control unit  213  as described.  FIG. 11  shows an example of a management switch table that the OpenFlow protocol processing unit  214  refers to when performing this processing.  FIG. 12  shows an example of a flow entry. 
       FIG. 13  is a drawing showing the correspondence relation between the virtual network shown in  FIG. 5  and the real network configuration shown in  FIG. 2 . For instance, when the physical node  10  # 1  in  FIG. 13  receives a packet from the port connected to the external network, the physical node  10  # 1  will issue an inquiry to the OpenFlow protocol processing unit  214  of the control server  20  if there is no entry matching this packet in the flow table  12 . The OpenFlow protocol processing unit  214  adds an ID of the physical node  10  # 1  and the port number to this inquiry and forwards it to the virtual network control unit  212 . The virtual network control unit  212  performs physical-virtual conversion on the received packet by referring to the virtual network configuration information storage unit  202  and the virtual network identifying information storage unit  203  and suitably performs network processing using the virtual node emulation unit  211  assuming that the packet is supplied to a virtual network indicated in the upper part of  FIG. 11 . Then, the virtual network control unit  212  performs physical-virtual conversion again on the processing result from the virtual node emulation unit  211 , and supplies the result to the path control unit  213 . Here, for instance, if a result that the packet should be outputted from a port of the physical node  10  # 2  connected to an HTTP server  1  is obtained from the result of virtual-physical conversion on the output of the virtual node emulation unit  211 , and the path control unit  213  calculates that a path from the physical node  10  # 1  to the physical node  10  # 2  is the shortest, the OpenFlow protocol processing unit  214  controls so that the packet is outputted from the physical port corresponding to the virtual interface of the physical node ID  10  # 2  and instructs the physical node  10  # 1  and the physical node  10  # 2  on the path to update the flow tables so that subsequent packets will be similarly processed. 
     As described, network processing equivalent to the virtual network in the upper part of  FIG. 13  is realized by the combination of the physical nodes  10  # 1  to  10  # 3  and the control server  20  shown in the lower part of  FIG. 13 . One of the benefits of this configuration is that, even if the configurations of the physical node and HTTP server are physically changed, this can be addressed by modifying the table used in physical-virtual conversion and illustrated in  FIG. 10 , and maintenance property will improve. For instance, when the physical node  10  # 1  shown in the lower part of  FIG. 13  is replaced, this can be addressed by modifying the table used in physical-virtual conversion and illustrated in  FIG. 10  and does not influence the configuration of the virtual network (refer to the upper part of  FIG. 13 ) visible to a user. 
     Next, with reference to  FIGS. 14 to 17 , a sequence of the operation of the present exemplary embodiment is organized and described. In the explanation below, it is assumed that the physical node # 1  has received a new packet from a user terminal connected to the external network. Further, to simplify the description, it is assumed that one virtual router is provided as a virtual node in the virtual network. 
     As shown in  FIG. 14 , upon receiving a packet, the physical node # 1  searches for an entry having a matching key that matches this packet in the flow table  12  (step S 001 ). 
     Here, it is assumed that this packet is the first packet and no entry corresponding to the received packet is registered in the flow table of the physical node # 1 . Therefore, the physical node # 1  issues an inquiry with the port number (input port number) that received the packet and the packet to the control server  20 , and requests the control server to generate and transmit a flow entry (step S 002 ; packet receipt notification (Packet-In)). 
     Upon receiving the packet receipt notification (Packet-In), the OpenFlow protocol processing unit  214  of the control server  20  adds the source physical node ID (input physical node) of the packet receipt notification (Packet-In) and forwards the packet to the virtual network control unit  212  (step S 003 ). Note that the physical node ID can be derived from the management switch table shown in  FIG. 11  or a security channel identifier (SecChan identifier) that received this packet. 
     The virtual network control unit  212  stores the received packet in the packet cache  215  and performs virtual-physical conversion on the packet by referring to the virtual network identifying information illustrated in  FIG. 10  using the physical node ID (input physical node) of the packet source, the input port number, and header information (step S 004 ). Note that the packet cache  215  may be omitted, and in this case the step in which the received packet is stored in the packet cache  215  is omitted. 
     Next, as shown in  FIG. 15 , when the virtual network control unit  212  supplies the packet after the virtual-physical conversion to the virtual router, the virtual router resolves the virtual interface ID of the packet source by referring to the routing table illustrated in  FIG. 7A  and transmits the packet whose MAC address has been rewritten (step S 005 ). 
     The virtual network control unit  212  resolves the physical node ID that outputs the packet and the physical port ID thereof by performing a reverse lookup on the virtual network identifying information illustrated in  FIG. 10  using the virtual interface ID of the transmitted packet, and resolves the contents of header conversion instructed to this physical node by comparing the packet stored in the packet cache  215  at the time of the reception and the header information of the transmitted packet (step S 006 ). Further, if the packet cache  215  is not provided in the virtual network control unit  212 , a solution such as a method for receiving a matching packet from the path control unit  213  may be suitably employed. 
     Next, the virtual network control unit  212  requests setting of a flow entry that includes the input physical node, the input port number, the header information, the resolved physical node ID and the physical port ID outputting the packet, and the header conversion contents. 
     Next, as shown in  FIG. 16 , the path control unit  213  that has received the request for setting the flow entry resolves the shortest path from the input physical node to the output physical node (step S 007 ). The path control unit  213  transmits the received packet to the physical node # 2 , instructs the physical node # 2  to output the packet from a designated port, and requests the OpenFlow protocol processing unit  214  to add a flow entry that realizes the resolved shortest path. 
     The physical node # 2  outputs a received packet from the designated port according to the instruction from the path control unit  213  (step S 008 ). Further, at this time, the OpenFlow protocol processing unit  214  may have the physical node # 2  execute an action of obtaining an IP DA (Internet Protocol Destination Address) from the header of the received packet, transmitting an ARP request to ports other than the port that received the received packet, and obtaining a corresponding MAC DA. 
     Further, the OpenFlow protocol processing unit  214  creates a flow entry to each physical node corresponding to the specified shortest path and transmits the flow entries to the physical nodes # 1  and # 2  (flow entry adding request; FlowMod (Add)). At this time, the OpenFlow protocol processing unit  214  sends a flow entry defining an action of converting the header to the physical node # 2  as well. 
     The physical nodes # 1  and # 2  add the flow entries to the flow tables  12  according to the instruction from the OpenFlow protocol processing unit  214  (step S 009 ). 
     Then, as shown in  FIG. 17 , since the set flow entry is detected in a search in the flow table  12  (step S 101 ), the physical node # 1  successively forwards subsequent packets to the physical node # 2  without issuing an inquiry to the control server  20  (step S 102 ). 
     Similarly, since the set flow entry is detected in a search in the flow table  12  (step S 103 ), the physical node # 2  successively outputs the packets received from the physical node # 1  from the designated port (step S 104 ). 
     Although this is omitted in  FIGS. 14 to 17 , the same processing is performed in a flow so which the physical nodes # 1  and # 2  in  FIGS. 14 to 17  are switched when a response to the packet is transmitted from the packet output destination of the physical node # 2 . 
     In the exemplary embodiment described above, the explanation was given using an example in which a virtual router is provided as a virtual node, however, the firewall (FW) and the load balancer (LB) on the virtual network shown in  FIG. 5  can be similarly realized by defining the behavior of the physical node. 
     For instance, when the virtual node emulation unit  211  is operated as a firewall according to a firewall policy of performing filtering operation by referring to the header information of a particular layer, a function equivalent to the firewall on the virtual network can be realized by setting an action of having the physical node receive the packet outputted from the virtual router and drop a corresponding packet based on the result thereof. 
     Similarly, for instance, a function equivalent to the load balancer on the virtual network can be realized by setting an action of supplying an output from the firewall to the virtual node emulation unit  211  that operates according to a predetermined load balance policy and switching the destination of the packet based on the result thereof. 
     The exemplary embodiment of the present invention has been described above, however, the present invention is not limited to the above exemplary embodiment and further modifications, replacements, and adjustments can be added within the scope of the basic technological concept of the present invention. For instance, the OpenFlow switch is used as the physical node and the OpenFlow protocol is used in the communication between the physical node and the control server in the exemplary embodiment described above, however, the present invention is not limited to the example above and any switch or protocol having the same functions can be used. For instance, the physical node can be realized by a router on an IP network or an MPLS switch on an MPLS (Multi-Protocol Label Switching) network, in addition to the OpenFlow switch. 
     It should be noted that within the entire disclosure (including the claims) and based on the fundamental technical concept, modifications and/or adjustment of the disclosed exemplary embodiments or examples may be done. Also various combination and selection of the various disclosed elements may be done within the scope of the claims of the present invention. That is, variations or modifications that may be done by the person of ordinary skill in the art based on the entire disclosure and technical concept including the claims may be included. 
     EXPLANATIONS OF SYMBOLS 
     
         
           10 ,  10  # 1 ,  10  # 2 ,  10  # 3 : physical node 
           11 : server communication unit 
           12 : flow table 
           13 : control unit 
           20 : control server 
           30 : external node 
           201 : virtual node object storage unit 
           202 : first storage unit (virtual network configuration information storage unit) 
           203 : second storage unit (virtual network identifying information storage unit) 
           204 : physical topology information storage unit 
           205 : shortest path information storage unit 
           206 : set flow forwarding path information storage unit 
           207 : flow entry storage unit 
           208 : management switch information storage unit 
           210 : control unit 
           211 : virtual node emulation unit 
           212 : virtual network control unit 
           213 : path control unit 
           214 : OpenFlow protocol processing unit 
           215 : packet cache