Patent Publication Number: US-2013243004-A1

Title: Communication control method, relay device, and information processing device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2012-059949, filed on Mar. 16, 2012, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a communication control method, a relay device, and an information processing device. 
     BACKGROUND 
     With Ethernet, Media Access Control (hereinafter may also be referred to as simply “MAC”) addresses are assigned to interfaces of communication devices thereupon, representing each interface. The interfaces of the communication devices are coupled to a small-scale network domain called a Local Area Network (hereinafter may also be referred to as simply “LAN”). A MAC address is an example of a physical address. 
     Also, when communication devices use Internet Protocol (hereinafter may also be referred to as simply “IP”) on an Ethernet, IP addresses are assigned to interfaces of communication devices thereupon, representing the logical network to which the interfaces are coupled, and the interfaces themselves. An IP address is made up of an identifier of a logical network and an identifier of a interface on the logical network. An IP address is an example of a logical address. 
     When transmitting packets to another communication device on the same logical network, a communication device broadcasts a message (MAC address resolution request), requesting the MAC addresses of the interface of the communication device having the IP address of the interface of the destination communication device (destination IP address), over the LAN to which the interfaces of the communication devices belonging to that logical network are coupled. 
     The destination communication device receives the MAC address resolution request, generates a response message including a MAC address which has been assigned to its own interface, and returns the generated response message responding to the MAC address resolution request (MAC address resolution response) to the source communication device. 
     The source communication device receives the response message regarding the MAC address resolution request (MAC address resolution response) from the destination communication device. The source communication device transmits a packet to be transmitted to the destination communication device, as an Ethernet frame (hereinafter may also be referred to as simply “frame”), of which the destination of the communication device having the MAC address included in the MAC address resolution response. 
     In order to execute the above-described transmission operations, the MAC address resolution request that has been broadcast has to reach all communication devices on the logical network. Since a broadcast only reaches devices coupled to the same LAN, communication devices on the same logical network are generally coupled to the same LAN. 
     Work is being done on LISP (Locator/ID Separation Protocol draft-ietf-lisp-15) by IETF (Internet Engineering Task Force), which is a technology that allows packets transmitted from a communication device situated outside of the logical network to be transmitted to a router (or a gateway) to which is coupled the communication device having the destination IP address. 
     SUMMARY 
     According to an aspect of the invention, a communication control method of a communication system including a first communication device, a first relay device coupled to the first communication device via a first network which is a network domain where a message broadcasted from the first communication device reaches and where communication based on physical addresses is performed, and a second communication device belonging to the same logical network to which the first communication device belongs, the communication control method including: broadcasting, by the first communication device, a first request including a logical address assigned to the second communication device and requesting a physical address assigned to the second communication device, transmitting, by the first relay device, in the event that the second communication device is not coupled to the first network, a first response which is a response to the first request and includes a predetermined physical address, to the first communication device. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating the configuration of a communication system operating based on LISP. 
         FIG. 2  is a sequence chart for describing a communication control method with the communication system. 
         FIG. 3  is a diagram illustrating the configuration of a communication system according to a first embodiment. 
         FIGS. 4A and 4B  are diagrams illustrating examples of locator lists. 
         FIGS. 5A and 5B  are diagrams illustrating examples of IP address/router ID maps. 
         FIG. 6  is a diagram illustrating a router ID/locator map. 
         FIG. 7  is a sequence chart for describing a communication control method with the communication system in  FIG. 3 . 
         FIG. 8  is a functional block diagram illustrating the configuration of a router according to the first embodiment. 
         FIG. 9  is a hardware configuration diagram illustrating the configuration of the router. 
         FIG. 10  is a functional block diagram illustrating the configuration of a location management server according to the first embodiment. 
         FIG. 11  is a hardware configuration diagram illustrating the configuration of the location management server. 
         FIG. 12  is a diagram illustrating the configuration of a communication system according to a second embodiment. 
         FIG. 13  is a diagram illustrating an example of an of IP address/locator map. 
         FIG. 14  is a functional block diagram illustrating the configuration of a location management server according to the second embodiment. 
         FIG. 15  is a diagram illustrating the configuration of a communication system according to a third embodiment. 
         FIGS. 16A to 16C  are diagrams illustrating examples of locator lists. 
         FIG. 17  is a diagram illustrating an example of an IP address/LAN ID map. 
         FIG. 18  is a diagram illustrating an example of a LAN ID/router ID map. 
         FIG. 19  is a diagram illustrating an example of a router ID/locator map. 
         FIG. 20  is a functional block diagram illustrating the configuration of a location management server according to the third embodiment. 
         FIG. 21  is a diagram illustrating the configuration of a communication system according to a fourth embodiment. 
         FIG. 22  is a diagram illustrating an example of an IP address/locator cache map. 
         FIG. 23  is a sequence chart for describing a communication control method with the communication system in  FIG. 21 . 
         FIG. 24  is a diagram illustrating the configuration of a router according to the fourth embodiment. 
         FIG. 25  is a diagram illustrating the configuration of a communication system according to a fifth embodiment. 
         FIGS. 26A to 26C  are diagrams illustrating an example of IP address/MAC address cache maps before changing of a LAN to which a communication device is coupled. 
         FIGS. 27A to 27C  are diagrams illustrating an example of IP address/MAC address cache maps after changing of the LAN to which the communication device is coupled. 
         FIG. 28  is a diagram illustrating the configuration of a communication system according to a sixth embodiment. 
         FIG. 29  is a diagram illustrating an example of a proxy MAC address response list. 
         FIG. 30  is a diagram illustrating an example of an IP address/MAC address map. 
         FIG. 31  is a sequence chart for describing a communication control method with the communication system in  FIG. 28 . 
         FIG. 32  is a diagram illustrating the configuration of a router according to the sixth embodiment. 
         FIG. 33  is a functional block diagram illustrating the configuration of a location management server according to the sixth embodiment. 
         FIG. 34  is a diagram illustrating the configuration of a communication system according to a seventh embodiment. 
         FIG. 35  is a sequence chart for describing a communication control method with the communication system in  FIG. 34 . 
         FIG. 36  is a diagram illustrating the configuration of a router according to the seventh embodiment. 
         FIG. 37  is a functional block diagram illustrating the configuration of a location management server according to the seventh embodiment. 
         FIG. 38  is a diagram illustrating the configuration of a communication system according to an eighth embodiment. 
         FIGS. 39A to 39C  are diagrams illustrating examples of locator lists. 
         FIG. 40  is a diagram illustrating an example of an IP address/LAN ID map. 
         FIG. 41  is a diagram illustrating an example of a LAN ID/router ID map. 
         FIG. 42  is a diagram illustrating an example of a router ID/locator map. 
         FIG. 43  is a functional block diagram illustrating the configuration of a location management server according to the eighth embodiment. 
         FIG. 44  is a diagram illustrating the configuration of a communication system according to a ninth embodiment. 
         FIG. 45  is a sequence chart for describing a communication control method with the communication system in  FIG. 44 . 
         FIG. 46  is a diagram illustrating the configuration of a router according to the ninth embodiment. 
         FIG. 47  is a functional block diagram illustrating the configuration of a location management server according to the ninth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In recent years, there has come to be demand for operating multiple LANs at physically remote locations as a single logical network, such as with a data center network, for example. 
     However, in this case, broadcasts only reach devices coupled on the same LAN, so a MAC address resolution request transmitted from a communication device belonging to one LAN does not reach communication devices belonging to another LAN. 
     Accordingly, in a case where a source communication device and a destination communication device belong to the same logical network but belong to different LANs, the source communication device which has transmitted a MAC address resolution request does not receive a corresponding MAC address resolution response from the destination communication device, and thus does not recognize the MAC address of the interface of the destination communication device. 
     Consequently, there has been a problem in that packet communication is not properly carried out between communication devices belonging to the same logical network. 
     It is an aim of embodiments described herein to provide a communication control method enabling packet communication between communication devices belonging to the same logical network, even with a communication system in which a logical network is configured of multiple LANs. 
     The following is a description of embodiments. 
     1. About LISP 
     Before describing the embodiments, the aforementioned LISP will be described. 
       FIG. 1  is a diagram illustrating the configuration of a communication system  100  operating based on LISP, and  FIG. 2  is a sequence chart for describing a communication control method with the communication system  100 . 
     With the communication system  100  illustrated in  FIG. 1 , communication devices  104  and  106  belong to the same logical network  102 , but to different LANs. The communication device  104  belongs to a LAN  108 , and is coupled to a network  116  via a corresponding router  112 . The communication device  106  belongs to a LAN  110 , and is coupled to the network  116  via a corresponding router  114 . 
     Also, a location management server  122  is coupled to the network  116 . The location management server  122  includes a storage device holding an IP address/router ID map  126  and Router ID/locator map  128 . The IP address/router ID map  126  is a table representing the relation between the IP addresses of the interfaces of the communication devices coupled to the network  116 , and identification information (router ID) of corresponding routers. The router ID/locator map  128  is a table representing the relation between the identification information (router ID) of each router coupled to the network  116 , and the corresponding locators. 
     Now, communication control performed in a case where a packet is transmitted to the communication device  104  belonging to the logical network  102  from a communication device  120  situated outside of the logical network  102 , with reference to  FIG. 2 . 
     As illustrated in  FIG. 2 , in step S 202 , the communication device  120  transmits of packet, of which the destination is the interface of the communication device  104 , to the corresponding router  118 . The transmitted packet includes the IP address of the interface of the communication device  104 , as a destination IP address (destination IP address). 
     The communication device  104  belongs to the logical network  102  unlike the communication device  120 , and does not exist beneath the router  118 . Accordingly, upon having received the packet from the communication device  120  in step S 204 , the router  118  transmits a message requesting a locator correlated with the destination IP address included in the received packet (locator resolution request) to the location management server  122 . The transmitted locator resolution request includes the destination IP address included in the received packet. 
     Upon receiving the locator resolution request in step S 206 , the location management server  122  searches the IP address/router ID map  126  that is held, and acquires identification information (router ID) of the router correlated with the destination IP address included in the received locator resolution request. Further, the location management server  122  searches the router ID/locator map  128  that is held, and acquires the locator correlated with the acquired router ID. With the example illustrated in  FIG. 1 , the acquired locator is “10.1.1.1”, and the destination which the locator indicates is the interface of the router  112  to which the communication device  104  is coupled. The location management server  122  transmits a response message including the acquired locator (locator resolution response) to the router  118 . 
     Note that in the following embodiments, the series of processing executed in steps S 204  and S 206 , and equivalent processing, will be referred to as “locator resolution processing”. 
     In step S 208 , the router  118  receives the locator resolution response, encapsulates the received packet, and transmits this as to the locator included in the received locator resolution response (“10.1.1.1” in the example illustrated in  FIG. 1 ) via the network  116 . 
     In step S 210 , the router  112  decapsulates the encapsulated packet received from the router  118 . Subsequently, the router  112  transmits the packet acquired by decapsulating to the interface of the communication device  104  having the destination IP address. 
     As described above, with LISP, the location management server  122  holds the IP address/router ID map  126  and router ID/locator map  128 , and functions to notify each router coupled to the network  116  of location information of the locator corresponding to the interface of the communication device having the destination IP address. 
     With the embodiments described below, in order to perform packet communication with a communication system in which a logical network is made up of multiple LANs, the aforementioned locator location information held by the location management server  122  is used to employ the locator location information notification function of the location management server  122 . 
     2. First Embodiment 
     The following is a description of a communication system, communication control method, relay device, and information processing device, according to a first embodiment. 
     2-1. Configuration of Communication System  300   
       FIG. 3  is a diagram illustrating the configuration of a communication system  300  according to the first embodiment,  FIG. 4A  is a diagram illustrating an example of a locator list  332 ,  FIG. 4B  is a diagram illustrating an example of a locator list  334 ,  FIG. 5A  is a diagram illustrating an example of an IP address/router ID map  326 ,  FIG. 5B  is a diagram illustrating another example of the IP address/router ID map  326 , and  FIG. 6  is a diagram illustrating a router ID/locator map  328 . 
     As illustrated in  FIG. 3 , the communication system  300  includes communication devices  304  and  306 , routers  312  and  314 , and a location management server  322 , and operates based on the above-described LISP. 
     A corresponding IP address and MAC address are assigned to each interface of the communication devices and routers. Coupled to each LAN is the interface or interfaces of one or multiple communication devices, with one or multiple routers coupled thereto. One or multiple locators are assigned to each router. 
     With the communication system  300 , each LAN  308  and  310  is a network domain configured of communication devices, relay devices, and so forth, capable of executing L2 communication based on Layer 2 (which is the data link layer, also written as “L2”) communication protocol, assuming message communication within the LANs  308  and  310  to be performed by L2 communication based on MAC addresses. Also, the LANs  308  and  310  are each network domains within a range where messages broadcast from a communication device coupled to that LAN will reach. 
     The communication devices  304  and  306  belong to the same logical network  302 , but each belong to different LANs. Here, a logical network is defined as being a network domain which is either physically located at one location, or is handled logically as a single network regardless of being configured of multiple LANs. A logical network may be configured of a single LAN, as well. 
     The communication device  304  belongs to the LAN  308 , and is coupled to the network  316  via the corresponding router  312 . The communication device  306  belongs to the LAN  310 , and is coupled to the network  316  via the corresponding router  314 . The network  316  is configured of communication devices, relay devices, and so forth, capable of executing L3 communication based on Layer 3 (which is the network layer, also written as “L3”) communication protocol, assuming message communication within the network  316  to be performed by L3 communication based on IP addresses. 
     The router  312  has an interface coupled to the communication device  304  via the LAN  308 , and two interfaces coupling to the network  316 . The router  312  includes a storage device holding the locator list  332 . The router  312  is a relay device to relay packet communication between the communication device  304  and the network  316 , and operates based on the above-described LISP. 
     The locator list  332  is a list indicating locators assigned to the router  312 . As indicated in  FIG. 4A , the locator list  332  includes two locators, meaning that two locators (10.1.1.1, 10.1.2.1) are assigned to the router  312 . 
     Upon receiving a MAC address resolution request from a communication device belonging to the corresponding LAN  308 , the router  312  transmits a locator resolution request to the location management server  322 . The locator resolution request that is transmitted here includes the destination IP address included in the received MAC address resolution request. 
     Subsequently, the router  312  receives a locator resolution response corresponding to the locator resolution request from the location management server. In the event that the locator included in the received locator resolution request is not included in the locator list  332 , the router  312  performs processing to transmit a response message (MAC address resolution response) including the MAC address of its own interface, to the source communication device of the MAC address resolution request (Proxy MAC address response processing). Details of the Proxy MAC address response processing at the router  312  will be described later. 
     The router  314  has an interface coupled to the communication device  306  via the LAN  310 , and has an interface coupled to the network  316 . The router  314  includes a storage device which holds the locator list  334 . The router  314  is a relay device to relay packet communication between the communication device  306  and the network  316 , and operates based on the above-described LISP. 
     The locator list  334  is a list indicating a locator assigned to the router  314 . As indicated in  FIG. 4B , the locator list  334  includes one locator, meaning that one locator (10.2.1.1) is assigned to the router  314 . 
     In the same way as with the router  312 , in the event that the locator included in the received locator resolution request is not included in the locator list  334 , the router  314  performs processing to transmit a response message (MAC address resolution response) including the MAC address of its own interface, to the source communication device of the MAC address resolution request (Proxy MAC address response processing). Details of the Proxy MAC address response processing at the router  314  will be described later. 
     The location management server  322  is an information processing device which is coupled to the network  316  and operates based on the above-described LISP. The location management server  322  includes a storage device holding the IP address/router ID map  326  and a storage device holding the router ID/locator map  328 . 
     The location management server  322  receives locator resolution requests including a destination IP address from the routers coupled to the network  316 . The location management server  322  acquires a locator correlated with a destination IP addresses included in a received locator resolution request, by searching the IP address/router ID map  326  and router ID/locator map  328 , and transmits a response message including the acquired locator (locator resolution response) to the source router of the locator resolution request. Note that the IP address/router ID map  326  and the router ID/locator map  328  may be held in a single storage device. 
     The IP address/router ID map  326  is a table representing the relation between IP addresses of the interfaces of the communication devices coupled to the network  316 , and identification information of corresponding routers (router IDs). As illustrated in  FIG. 5A , the IP address “192.168.1.1” of the interface of the communication device  304  and the router ID “R1” of the router  312  are correlated, and the IP address “192.168.2.2” of the interface of the communication device  306  and the router ID “R2” of the router  314  are correlated. That is to say, two different routers  312  and  314  are correlated with the interfaces of the two communication devices  304  and  306  belonging to the same logical network  302 . 
     While the example illustrated in  FIG. 5A  is of a format where an entry is provided in the IP address/router ID map  326  for every IP address, this is not restrictive. For example, an arrangement may be made such as illustrated in  FIG. 5B , where IP addresses in the IP address/router ID map  326  are replaced with a network address mask format, and router IDs are correlated with an aggregation of IP addresses of multiple interfaces and the correlation is held therein. 
     The router ID/locator map  328  is a table representing the relation between identification information of the routers coupled to the network  316  (router IDs) and corresponding locators. As illustrated in  FIG. 6 , the router ID “R1” of the router  312  is correlated with the two locators “10.1.1.1” and “10.1.2.1” of the router  312 , and the router ID “R2” of the router  314  is correlated with the one locator “10.2.1.1” of the router  314 . That is to say, the router  312  has two locators correlated with a single router ID. 
     Note that in the above-described embodiment, a router has been exemplified as a relay device relaying communication between the communication devices and the network, but the relay device is not restricted to a router, and may be another device having relay functions. 
     2-2. Communication Control Method with Communication System  300   
       FIG. 7  is a sequence chart for describing a communication control method with the communication system  300 . Description will now be made regarding a communication control method with the communication system  300  in a case of transmitting packets from the interface of the communication device  304  to the interface of the communication device  306  belonging to the same logical network, with reference to  FIG. 3  in addition to  FIG. 7 . 
     As illustrated in  FIG. 7 , in step S 702  the communication device  304  broadcasts a message requesting the MAC address of the interface of the communication device  306  which is the destination (MAC address resolution request) to the LAN  308  to which its own interface is coupled, in order to transmit packets to the interface of the communication device  306 . The MAC address resolution request that is transmitted includes the IP address of the interface of the communication device  306  which is the destination (destination IP address). An example of a MAC address resolution request is an ARP (Address Resolution Protocol) request. In the example illustrated in  FIG. 3 , the transmitted MAC address resolution request includes “192.168.2.2” as the destination IP address. 
     The communication device  304  determines whether or not the communication device  306  belongs to the same logical network as itself, by matching the destination IP address of the communication device  306  and the logical network address assigned to itself. With the example illustrated in  FIG. 3 , the destination IP address of the communication device  306  is “192.168.2.2”, and the logical network address assigned to the communication device  304  is “192.168.0.0/16”, so the communication device  304  determines whether or not the upper 16 bits of the addresses “192.168.2.2” and “192.168.0.0” match. Here, the upper 16 bits of the two addresses match each other, so the communication device  304  recognizes that the communication device  306  belongs to the same logical network as itself. 
     Next, upon having received the MAC address resolution request from the communication device  304 , in step S 704  the router  312  transmits a message requesting a locator (destination locator) correlated with the destination IP address included in the received MAC address resolution request (locator resolution request) to the location management server  322 . A locator resolution request includes the destination IP address included in the received MAC address resolution request. With the example illustrated in  FIG. 3 , the transmitted locator resolution request includes “192.168.2.2” as a destination IP address. 
     Note that each router coupled to the network  316  has acquired beforehand the IP address of the location management server  322  (“10.10.1.1” in the example illustrated in  FIG. 3 ), and may transmit locator resolution requests to the location management server  322  using this IP address. 
     The location management server  322  receives the locator resolution request from the router  312  in step S 706 . The location management server  322  acquires identification information of the router correlated with the destination IP address (router ID) by searching the IP address/router ID map  326  that is held, based on the destination IP address included in the received locator resolution request. With the example illustrated in  FIGS. 3 and 7 , the destination IP address is “192.168.2.2”, and according to the map illustrated in  FIG. 5A  the acquired router ID is “R2”. 
     Further, the location management server  322  acquires the locator corresponding to the acquired router ID by searching the router ID/locator map  328  that is held, based on the acquired router ID. With the example illustrated in  FIGS. 3 and 7 , the router ID is “R2”, and according to the map illustrated in  FIG. 6  the acquired locator is “10.2.1.1”. 
     Thus, the location management server  322  acquires locators correlated with destination IP addresses included in locator resolution requests received from the router  312 , by the above-described locator acquisition processing. The location management server  322  transmits a response message including the acquired locator (locator resolution response) to the router  312 . With the example illustrated in  FIGS. 3 and 7 , one locator “10.2.1.1” is acquired as to the destination IP address “192.168.2.2”. The destination which the acquired locator indicates is one interface of the router  314  to which the communication device  306  is coupled, and the locator resolution response includes “10.2.1.1” as the locator. 
     Note that in the event that multiple locators have been assigned to a router coupled to the interface of the destination communication device  306 , or in the event that the interface of the destination communication device  306  is coupled to multiple routers, unlike the example illustrated in  FIG. 3 , multiple locators will be correlated to one destination IP address included in the locator resolution request. In such a case, the locator resolution response will include multiple locators, so the location management server  322  will transmit a locator resolution response including multiple locators to the source router of the locator resolution request. 
     Next, in step S 706 , the router  312  receives the locator resolution response from the location management server  322 , and in step S 708  checks whether or not the locator included in the received locator resolution response is include in its own locator list  332 , by referencing the locator list  332  that is held. 
     With the example illustrated in  FIG. 3 , the router  312  checks that the locator “10.2.1.1” included in the locator resolution response is not included in its own locator list  332 , based on the locator list  332  illustrated in  FIG. 4A . Accordingly, the router  312  recognizes that the interface of the communication device  306  having the destination IP address does not belong to the LAN  308 . 
     Next, in step S 710 , the router  312  transmits to the communication device  304  a response message corresponding to the MAC address resolution request relieved in step S 702  (MAC address resolution response). An example of a MAC address resolution response is an ARP response. 
     At this time, the router  312  assigns the MAC address of the interface of itself to the MAC address resolution response. With the example illustrated in  FIG. 3 , the MAC address “MR1” of the interface of the router  312  that is coupled to the LAN  308  is assigned. That is to say, the router  312  generates a response message (MAC address resolution response) using the MAC address of its own interface as a proxy for the communication device  306  which originally is supposed to respond to the MAC address resolution request, and performs Proxy MAC address response processing with the generated MAC address resolution response. 
     By recognizing that the interface of the communication device  306  does not belong to the LAN  308 , the router  312  recognizes that in the current state, the communication device  304  which has transmitted the MAC address resolution request will not receive a corresponding MAC address resolution response, and accordingly will not recognize the MAC address of the interface of the communication device  306 . Accordingly, the router  312  executes the above-described Proxy MAC address response processing with regard to the communication device  304 , so as to avoid a situation in which packet transmission from the communication device  304  to the interface of the communication device  306  is not started. 
     Note that with the embodiments in the Present Specification, the series of processing executed in steps S 704  through S 710 , and equivalent processing, will be referred to as “Proxy MAC address response processing”. 
     Next, in step S 712 , the communication device  304  receives a MAC address resolution response from the router  312 , and recognizes the MAC address of the interface of the router  312  that is included in the received MAC address resolution response as being the MAC address which is the destination (destination MAC address). The communication device  304  transmits a packet which is a message of which the destination is the interface of the communication device  306 , as a frame which is a message with the corresponding router  312  interface as the destination thereof. At this time, the transmitted frame includes the IP address of the destination communication device  306  interface as the destination IP address, and also includes the MAC address of the interface of the router  312  that is included in the received MAC address resolution response as the destination MAC address. With the example illustrated in  FIG. 3 , the transmitted frame includes “192.168.2.2” as the destination IP address and also includes “MR1” as the destination MAC address. 
     Next, in step S 714 , the router  312  receives the frame from the communication device  304 . The router  312  and location management server  322  use the destination IP address included in the received frame, i.e., the IP address of the interface of the communication device  306 , to execute locator resolution processing. The locator resolution processing is processing similar to the processing executed in steps S 204  and S 206  in  FIG. 2 . 
     Upon receiving the frame from the communication device  304 , the router  312  extracts the packet from the received frame. The router  312  transmits a message requesting the locator correlated with the destination IP address included in the extracted packet (locator resolution request) to the location management server  322 . 
     The location management server  322  receives the locator resolution request from the router  312 . The location management server  322  searches the IP address/router ID map  326  so as to acquire identification information of the router (router ID) correlated with the destination IP address included in the received locator resolution request. With the example illustrated in  FIGS. 3 and 7 , the destination IP address is “192.168.2.2”, and according to the map illustrated in  FIG. 5A  the acquired router ID is “R2”. 
     Further, the location management server  322  acquires the locator corresponding to the acquired router ID by searching the router ID/locator map  328 . With the example illustrated in  FIGS. 3 and 7 , the router ID is “R2”, and according to the map illustrated in  FIG. 6  the acquired locator is “10.2.1.1”. 
     Thus, the location management server  322  acquires locators correlated with destination IP addresses included in locator resolution requests received from the router  312 , by the above-described locator acquisition processing. The location management server  322  transmits a response message including the acquired locator (locator resolution response) to the router  312 . With the example illustrated in  FIGS. 3 and 7 , one locator “10.2.1.1” is acquired as to the destination IP address “192.168.2.2”. The destination which the acquired locator indicates is one interface of the router  314  to which the communication device  306  is coupled, and the locator resolution response includes “10.2.1.1” as the locator. 
     Note that in the event that multiple locators have been assigned to a router coupled to the interface of the destination communication device  306 , or in the event that the interface of the destination communication device  306  is coupled to multiple routers, unlike the example illustrated in  FIG. 3 , multiple locators will be correlated to one destination IP address included in the locator resolution request. In such a case, the locator resolution response will include multiple locators, so the location management server  322  will transmit a locator resolution response including multiple locators to the source router of the locator resolution request. 
     Next, in step S 716 , the router  312  receives the locator resolution response, encapsulates the packet extracted from the received frame, and transmits this to the locator included in the received locator resolution response (“10.2.1.1” in the example illustrated in  FIG. 3 ) via the network  316 . The transmitted packet includes the destination locator (“10.2.1.1” in the example illustrated in  FIG. 3 ) and the destination IP address (“192.168.2.2” in the example illustrated in  FIG. 3 ). 
     Note that in the event that a locator resolution response including multiple destination locators has been received from the location management server  322 , the router  312  selects one of the multiple destination locators, and encapsulates the packet extracted from the received frame transmitted to the selected destination locator. Selection of one destination locator from the multiple destination locators may be performed by Round Robin, for example. 
     Next, in step S 718 , the router  314  decapsulates the encapsulated packet received from the router  312 . Subsequently, the router  314  acquires the MAC address that is the destination (destination MAC address) corresponding to the destination IP address (“192.168.2.2” in the example illustrated in  FIG. 3 ) included in the packet acquired by decapsualting. The router  314  transmits the received packet as a frame of which the destination is the interface of the communication device  306  having the destination MAC address that has been acquired. In the example illustrated in  FIG. 3 , the destination MAC address is “M2”. Note that acquisition of the destination MAC address may be performed by the above-described ARP request and ARP response processing. 
     As described above, with the communication system  300 , the router  312  to which the communication device  304  is coupled executes Proxy MAC address response processing as to the communication device  304  which has transmitted a MAC address resolution request, so packet communication is executable in a normal manner even with a case of performing packet communication between communication devices belonging to different LANs in a communication system where a logical network is configured of multiple LANs. 
     Also, with the communication system  300 , at the time of the router  312  deciding whether or not to execute Proxy MAC address response processing, maps (location information)  326  and  328  representing the relation between IP addresses and locators, which the location management server  322  operating based on LISP holds, are used. Accordingly, a database relating to location information of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     2-3. Configuration of Router  312  ( 314 ) 
       FIG. 8  is a functional block diagram illustrating the configuration of the router  312  ( 314 ) according to the first embodiment. 
     The functional block diagram illustrated in  FIG. 8  illustrates the portions of the router  312  ( 314 ) corresponding to the functions of the Proxy MAC address response processing described with reference to  FIG. 7 . Portions corresponding to other functions may use arrangements according to the related art, so description thereof will be omitted from the Present Specification. Also, while description will be made with regard to the configuration of the router  312 , the routers  312  and  314  have configurations which are equivalent to each other in the communication system  300 . 
     As illustrated in  FIG. 8 , the router  312  includes a MAC address resolution request processing unit  806 , a locator resolution request generating unit  810 , a locator resolution response processing unit  816 , a locator list  818 , and a MAC address resolution response generating unit  820 . 
     A transmission/reception unit  802  receives messages such as a MAC address resolution request from the LAN  308 , and outputs the received message to a message identification unit  804 . Also, the transmission/reception unit  802  receives a later-described MAC address resolution response from the MAC address resolution response generating unit  820 , and transmits the received MAC address resolution response to the interface of the source communication device of the MAC address resolution request, which will be described later, via the LAN  308 . 
     The message identification unit  804  identifies the content of the message received from the transmission/reception unit  802 , and in the event that the received message is a MAC address resolution request, the message identification unit  804  outputs the MAC address resolution request to the MAC address resolution request processing unit  806 . The output MAC address resolution request includes the destination IP address (IP address of the interface of the destination communication device) and the source MAC address (MAC address of the interface of the communication device which is the source of the MAC address resolution request). 
     The MAC address resolution request processing unit  806  receives the MAC address resolution request from the message identification unit  804 , and writes the information of the destination IP address and the source MAC address, included in the received MAC address resolution request, to a MAC address resolution request reception table  808 . Also, the MAC address resolution request processing unit  806  outputs the information of the destination IP address included in the received MAC address resolution request to the locator resolution request generating unit  810 . 
     The locator resolution request generating unit  810  receives the destination IP address from the MAC address resolution request processing unit  806 , and generates a locator resolution request including this destination IP address, based on the received destination IP address. The locator resolution request generating unit  810  outputs the generated locator resolution request to a transmission/reception unit  812 . 
     The transmission/reception unit  812  receives the locator resolution request from the locator resolution request generating unit  810 , and transmits the received locator resolution request to the location management server  322  via the network  316 . Also, the transmission/reception unit  812  receives a message such as a locator resolution response from the network  316  and outputs this to a message identification unit  814 . 
     The message identification unit  814  identifies the content of the message received from the transmission/reception unit  812 , and in the event that the received message is a locator resolution response, outputs the locator resolution response to the locator resolution response processing unit  816 . The output locator resolution response includes a destination IP address (IP address of the interface of the destination communication device) and destination locator (IP address of the interface of the packet destination router). 
     The locator resolution response processing unit  816  receives the locator resolution response from the message identification unit  814 , and acquires the information of the destination locator included in the received locator resolution response. By referencing the locator list  818 , the locator resolution response processing unit  816  checks whether or not the acquired destination locator is included in the locator list  818 . Note that the locator list  818  is the same as the locator list  332  ( 334 ) illustrated in  FIG. 3 . 
     In the event that the destination locator is not included in the locator list  818 , the locator resolution response processing unit  816  notifies the MAC address resolution response generating unit  820  to that effect, and outputs the destination IP address included in the received locator resolution response to the MAC address resolution response generating unit  820 . 
     The MAC address resolution response generating unit  820  receives the destination IP address from the locator resolution response processing unit  816 , and reads out the corresponding source MAC address from the MAC address resolution request reception table  808 , based on the received destination IP address. In the event that the destination locator is not included in the locator list  818 , the MAC address resolution response generating unit  820  further generates a MAC address resolution response, based on the received destination IP address and the source MAC address that has been read out. That is to say, the MAC address resolution response generating unit  820  generates a MAC address resolution response including its own (the router  312 ) MAC address, in addition to the destination IP address and source MAC address. The MAC address resolution response generating unit  820  outputs the generated MAC address resolution response to the transmission/reception unit  802 . 
       FIG. 9  is a hardware configuration diagram illustrating the configuration of the router  312  ( 314 ). The router  312  ( 314 ) includes a processor  902 , memory  904 , a storage device  906 , transmission/reception interfaces  908  and  910 , and a bus  912 . The processor  902 , memory  904 , storage device  906 , and transmission/reception interfaces  908  and  910  are each coupled to the bus  912 . The functions of the functional blocks of the router  312  ( 314 ) illustrated in  FIG. 8  may be realized by the hardware configuration of the router  312  ( 314 ) illustrated in  FIG. 9 . An example of the memory  904  is RAM, and examples of the storage device  906  include nonvolatile memory such as ROM or flash memory, and a magnetic disk device such as a hard disk drive (hereinafter may be referred to simply as “HDD”). 
     The functions and processing of the functional blocks of the message identification unit  804 , MAC address resolution request processing unit  806 , locator resolution request generating unit  810 , message identification unit  814 , locator resolution response processing unit  816 , and MAC address resolution response generating unit  820 , illustrated in  FIG. 8 , may be realized by the processor  902  executing processing programs in which are described corresponding functions and processing. Processing programs are stored in the storage device  906 , and the above-described functional blocks illustrated in  FIG. 8  are realized by the processor  902  loading the processing programs stored in the storage device  906  to the memory  904  and executing the processing described in the processing programs. 
     Also, the MAC address resolution request reception table  808  and locator list  818  illustrated in  FIG. 8  are stored in the memory  904  or storage device  906 . Write/read to/from the MAC address resolution request reception table  808  is performed by the processor  902  accessing the memory  904  or storage device  906  as desired with the locator list  818  being referenced, based on the processing described in the above-described processing program. 
     Note that in addition to the hardware configuration illustrated in  FIG. 9 , the above-described functional blocks illustrated in  FIG. 8  may be realized by a large-scale integrated circuit (hereinafter may be referred to simply as “LSI”) such as an ASIC (Application Specified Integrated Circuit) or FPGA (Field Programmable Gate Array). 
     The transmission/reception unit  802  illustrated in  FIG. 8  may be realized by the transmission/reception interface  908  capable of coupling to the LAN  308  ( 310 ), and the transmission/reception unit  812  may be realized by the transmission/reception interface  910  capable of coupling to the network  316 . The transmission/reception interfaces  908  and  910  each are input/output (hereinafter may be referred to simply as “I/O”) circuits according to the related art, for example. 
     As described above, the router  312  to which the communication device  304  is coupled executes Proxy MAC address response processing as to the communication device  304  which has transmitted a MAC address resolution request, so packet communication is executable in a normal manner even with a case of performing packet communication between communication devices  304  and  306  belonging to different LANs. 
     2-4. Configuration of Location Management Server  322   
       FIG. 10  is a functional block diagram illustrating the configuration of the location management server  322  according to the first embodiment. 
     With the functional block diagram illustrated in  FIG. 10 , portions of the location management server  322  operating based on LISP described above which correspond to functions relating to the Proxy MAC address response processing and locator resolution processing described with reference to  FIG. 7  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. 
     As illustrated in  FIG. 10 , the location management server  322  includes a locator resolution request processing unit  1006 , a router ID searching unit  1008 , an IP address/router ID map  1010 , a locator searching unit  1012 , a router IP/locator map  1014 , and a locator resolution response generating unit  1016 . 
     The transmission/reception unit  1002  receives message such as locator resolution requests from the network  316  and outputs the received messages to a message identification unit  1004 . Also, a transmission/reception unit  1002  receives a later-described locator resolution response from the locator resolution response generating unit  1016 , and transmits the received locator resolution response to the source router of the locator resolution request, which will be described later, via the network  316 . 
     The message identification unit  1004  identifies the content of the message received from the transmission/reception unit  1002 , an in the event that the received message is a locator resolution request, outputs the locator resolution request to the locator resolution request processing unit  1006 . The output locator resolution request includes the destination IP address (the IP address of the interface of the destination communication device). 
     The locator resolution request processing unit  1006  receives the locator resolution request from the message identification unit  1004 , and notifies the information of the destination IP address included in the received locator resolution request to the router ID searching unit  1008 . 
     The router ID searching unit  1008  receives the destination IP address information from the locator resolution request processing unit  1006 , and acquires identification information of the router correlated with that destination IP address (destination router ID), by searching the IP address/router ID map  1010  based on the received destination IP address. The router ID searching unit  1008  notifies the information of the acquired destination router ID to the locator resolution request processing unit  1006 . Note that the IP address/router ID map  1010  is the same as the IP address/router ID map  326  illustrated in  FIG. 3 . 
     The locator resolution request processing unit  1006  receives the information of the destination router ID from the router ID searching unit  1008 , and notifies the information of the received destination router ID to the locator searching unit  1012 . 
     The locator searching unit  1012  receives the information of the destination router ID from the locator resolution request processing unit  1006 , and acquires the locator correlated with the destination router ID (destination locator) by searching the router ID/locator map  1014 , based on the received destination router ID. The locator searching unit  1012  notifies the locator resolution request processing unit  1006  of the information of the acquired destination locator. Note that the router ID/locator map  1014  is the same as the router ID/locator map  328  illustrated in  FIG. 3 . 
     The locator resolution request processing unit  1006  acquires the information of the destination locator from the locator searching unit  1012 . The locator resolution request processing unit  1006  notifies the locator resolution response generating unit  1016  of the acquired information of the destination locator, in addition to the destination IP address. 
     The locator resolution response generating unit  1016  receives the destination IP address and destination locator information from the locator resolution request processing unit  1006 , and generates a locator resolution response including the received destination IP address and destination locator. The locator resolution response generating unit  1016  outputs the generated locator resolution response to the transmission/reception unit  1002 . 
       FIG. 11  is a hardware configuration diagram illustrating the configuration of the location management server  322 . The location management server  322  includes a processor  1102 , memory  1104 , a storage device  1106 , a transmission/reception interface  1108 , and a bus  1112 . The processor  1102 , memory  1104 , storage device  1106 , and transmission/reception interface  1108  are each coupled to the bus  1112 . The functions of the functional blocks of the location management server  322  illustrated in  FIG. 10  may be realized by the hardware configuration of the location management server  322  illustrated in  FIG. 11 . An example of the memory  1104  is RAM, and examples of the storage device  1106  include nonvolatile memory such as ROM or flash memory, and a magnetic disk device such as an HDD. 
     The functions and processing of the functional blocks of the message identification unit  1004 , locator resolution request processing unit  1006 , router ID searching unit  1008 , locator searching unit  1012 , and locator resolution response generating unit  1016 , may be realized by the processor  1102  executing processing programs in which are described corresponding functions and processing. Processing programs are stored in the storage device  1106 , and the above-described functional blocks illustrated in  FIG. 10  are realized by the processor  1102  loading the processing programs stored in the storage device  1106  to the memory  1104  and executing the processing described in the processing programs. 
     Also, the IP address/router ID map  1010  and router ID/locator map  1014  illustrated in  FIG. 10  are stored in the memory  1104  or storage device  1106 . Searching of the IP address/router ID map  1010  and router ID/locator map  1014  is performed by the processor  1102  accessing the memory  1104  or storage device  1106  as desired, based on the processing described in the above-described processing program. 
     Note that in addition to the hardware configuration illustrated in  FIG. 11 , the above-described functional blocks illustrated in  FIG. 10  may be realized by an LSI an ASIC or FPGA. 
     The transmission/reception unit  1002  illustrated in  FIG. 10  may be realized by the transmission/reception interface  1108 . An example of the transmission/reception interface  1108  is an I/O circuit according to the related art. 
     As described above, at the time of the router  312  ( 314 ) deciding whether or not to execute Proxy MAC address response processing, the location management server  322  operating based on LISP acquires the destination locator using the maps (location information)  326  and  328  representing the relation between IP addresses and locators, which it holds itself. Accordingly, a database relating to location of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     3. Second Embodiment 
     The following is a description of a communication system, communication control method, relay device, and information processing device, according to a second embodiment. 
     3-1. Configuration of Communication System  1200   
       FIG. 12  is a diagram illustrating the configuration of a communication system  1200  according to the second embodiment.  FIG. 13  is a diagram illustrating an example of an IP address/locator map  1226 . 
     The communication system  1200  illustrated in  FIG. 12  differs from the communication system  300  illustrated in  FIG. 3  in that a location management server  1222  is provided instead of the location management server  322  and the IP address/locator map  1226  is provided instead of the IP address/router ID map  326  and router ID/locator map  328 , but other parts are the same. Parts which are the same as or equivalent to those in the communication system  300  in  FIG. 3  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 12  are the same as described with reference to  FIG. 3 , so detailed description will be omitted. 
     In  FIG. 12 , a location management server  1222  is an information processing device which is coupled to the network  316 , and operates based on the above-described LISP. The location management server  1222  includes a storage device which holds the IP address/locator map  1226 . The location management server  1222  searches the IP address/locator map  1226  and acquires locators correlated with destination IP addresses included in locator resolution requests received from the routers, and transmits response messages including the acquired locators (locator resolution responses) to the source routers of the locator resolution requests. 
     The IP address/locator map  1226  is a table representing the relation between the IP addresses of the interfaces of the communication devices coupled to the network  316 , and the IP addresses (locators) of the interfaces of the corresponding routers. As illustrated in  FIG. 13 , two locators “10.1.1.1” and “10.1.2.1” corresponding to the two interfaces of the router  312  are correlated with the IP address “192.168.1.1” of the interface of the communication device  304 , and the one locator “10.2.1.1” of the router  314  is correlated with the IP address “192.168.2.2” of the communication device  306 . That is to say, with the router  312 , two different locators are correlated with the interface of a single communication device. 
     3-2. Communication Control Method with Communication System  1200   
     The communication control method with the communication system  1200  differs from the communication control method of the communication system  300  illustrated in  FIG. 7  with regard to the locator acquisition processing executed in step S 706  and step S 714 , but other parts are the same. 
     The locator acquisition processing with the communication system  1200  differs from the locator acquisition processing with the communication system  300  with regard to the point that, at the time of acquiring a locator correlated with a destination IP address included in the locator resolution request, only the IP address/locator map  1226  is used, instead of using the two tables of the IP address/router ID map  326  and router ID/locator map  328 , but other parts are the same. 
     With the communication system  1200 , unlike the location management server  322 , in steps S 706  and S 714 , the location management server  1222  searches the IP address/locator map  1226  and acquires a locator correlated with a destination IP address included in the locator resolution request received from the router  312 , according to the above-described locator acquisition processing. In the examples illustrated in  FIGS. 7 and 12 , the destination IP address is “192.168.2.2”, and according to the map illustrated in  FIG. 13 , the acquired locator is “10.2.1.1”. 
     As described above, the location management server  1222  acquires a locator correlated with a destination IP address included in a locator resolution request received from the router  312 , by the above-described locator acquisition processing. The location management server  1222  transmits a response message including the acquired locator (locator resolution response) to the router  312 . In the examples illustrated in  FIGS. 7 and 12 , one locator of “10.2.1.1” is acquired as to the destination IP address “192.168.2.2”. The destination which the acquired locator indicates is the one interface of the router  314  to which the communication device  306  is coupled, and the locator resolution response includes “10.2.1.1” as the locator. 
     In step S 708 , the router  312  checks whether or not the locator included in the locator resolution response received from the location management server  1222  is included in the locator list  332 . In step S 710 , in response to a locator included in a locator resolution response not being included in its own locator list  332 , the router  312  performs Proxy MAC address response processing as to the communication device  304  by a MAC address resolution response including the MAC address of its own interface. 
     As described above, even in a case where packet communication is performed between communication devices belonging to different LANs with a communication system where one logical network is configured of multiple LANs, with the communication system  1200  the router  312  to which the communication device  304  which has transmitted a MAC address resolution response is coupled executes Proxy MAC address response processing as to the communication device  304 , so packet communication may be executed in a normal manner. 
     Also, with the communication system  1200 , at the time of the router  312  deciding whether or not to execute Proxy MAC address response processing, the map (location information)  1226  indicating the relation between IP addresses and locators, which the location management server  1222  operating based on LISP holds, is used. Accordingly, a database relating to location information of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     3-3. Configuration of Router  312  ( 314 ) 
     The configuration of the routers  312  and  314  in the communication system  1200  is the same as the configuration of the routers  312  and  314  in the communication system  300 . Accordingly, detailed description will be omitted. 
     3-4. Configuration of Location Management Server  1222   
       FIG. 14  is a functional block diagram illustrating the configuration of the location management server  1222  according to the second embodiment. 
     The location management server  1222  illustrated in  FIG. 14  differs from the location management server  322  illustrated in  FIG. 10  with regard to the point that a locator resolution request processing unit  1406  is provided instead of the locator resolution request processing unit  1006 , and locator searching unit  1408  and IP address/locator map  1410  are provided instead of the router ID searching unit  1008 , IP address/router ID map  1010 , locator searching unit  1012 , and router ID/locator map  1014 , but other parts are the same. Parts which are the same as or equivalent to those in the location management server  322  illustrated in  FIG. 10  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 14  are the same as described with reference to  FIG. 10 , so detailed description will be omitted. 
     With the functional block diagram illustrated in  FIG. 14 , in the same way as with the functional block diagram illustrated in  FIG. 10  portions of the location management server  1222  which correspond to functions relating to the Proxy MAC address response processing and locator resolution processing described with reference to  FIG. 7  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. 
     The locator resolution request processing unit  1406  receives a locator resolution request from the message identification unit  1004 , and notifies information of the destination IP address included in the received locator resolution request to the locator searching unit  1408 . 
     The locator searching unit  1408  receives the information of the destination IP address from the locator resolution request processing unit  1406 , and searches the IP address/locator map  1410  based on the received destination IP address, thereby acquiring a locator correlated with that destination IP address (destination locator). The locator searching unit  1408  notifies the information of the acquired destination locator to the locator resolution request processing unit  1406 . Note that the IP address/locator map  1410  is the same as the IP address/locator map  1226  illustrated in  FIG. 12 . 
     The locator resolution request processing unit  1406  acquires the information of the destination locator from the locator searching unit  1408 , and notifies the information of the acquired destination locator to the locator resolution response generating unit  1016 . 
     Note that the hardware configuration of the location management server  1222  is the same as the hardware configuration of the location management server  322  illustrated in  FIG. 11 . The functions of the functional blocks of the location management server  1222  may be realized with the same hardware configuration of the location management server  322  illustrated in  FIG. 11 . The IP address/locator map  1410  illustrated in  FIG. 10  is stored in memory or a storage device. Accordingly, detailed description will be omitted. 
     As described above, at the time of the router  312  ( 314 ) deciding whether or not to execute Proxy MAC address response processing, the location management server  1222  operating based on LISP acquires a destination locator using the IP address/locator map (location information)  1226 , and notifies the information of the acquired destination locator to the router  312  ( 314 ). Accordingly, a database relating to location information of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     4. Third Embodiment 
     The following is a description of a communication system, communication control method, relay device, and information processing device, according to a third embodiment. 
     4-1. Configuration of Communication System  1500   
       FIG. 15  is a diagram illustrating the configuration of a communication system  1500  according to a third embodiment,  FIGS. 16A through 16C  are diagrams illustrating an example of locator lists  332 ,  1534 , and  1544 ,  FIG. 17  is a diagram illustrating an example of an IP address/LAN ID map  1524 ,  FIG. 18  is a diagram illustrating an example of a LAN ID/router ID map  1526 , and  FIG. 19  is a diagram illustrating an example of a router ID/locator map  1528 . 
     The communication system  1500  illustrated in  FIG. 15  differs from the communication system  300  illustrated in  FIG. 3  with regard to the points that a router  1514  and locator list  1534  are provided instead of the router  314  and locator list  334 , and a router  1542  and locator list  1544  have been added. Further, the communication system  1500  differs from the communication system  300  with regard to the point that a location management server  1522  is provided instead of the location management server  322 , and that an IP address/LAN ID map  1524 , LAN ID/router ID map  1526 , and a router ID/locator map  1528 , are provided instead of the IP address/locator map  326  and router ID/locator map  328 . 
     Parts of the communication system  1500  other than those described above are the same as with the communication system  300 . Parts which are the same as or equivalent to those in the communication system  300  illustrated in  FIG. 3  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 15  are the same as described with reference to  FIG. 3 , so detailed description will be omitted. 
     In  FIG. 15 , the router  1514  has an interface coupled to the communication device  306  via the LAN  310 , and two interfaces coupled to the network  316 . The router  1514  includes a storage device holding the locator list  1534 . The router  1514  is a relay device which relays communication between the communication device  306  and the network  316 , and operates based on the above-described LISP. 
     The locator list  1534  is a list indicating locators assigned to the router  1514 . As illustrated in  FIG. 16B , the locator list  1534  includes two locators. That is to say, the router  1514  has assigned thereto two locators (10.2.1.1 and 10.2.2.1). 
     The router  1542  has an interface coupled to the communication device  306  via the LAN  310 , and an interface coupled to the network  316 . The router  1544  includes a storage device holding the locator list  1544 . The router  1542  is a relay device which relays communication between the communication device  306  and the network  316 , and operates based on the above-described LISP. 
     The locator list  1544  is a list indicating a locator assigned to the router  1542 . As illustrated in  FIG. 16C , the locator list  1544  includes one locator. That is to say, the router  1542  has assigned thereto one locators (10.3.1.1). 
     Note that  FIG. 16A  illustrates an example of the locator list  332 , which is the same as that in  FIG. 4A . 
     The location management server  1522  Is coupled to the network  316 , and is an information processing device which operates based on the above-described LISP. The location management server  1522  has coupled thereto a storage device holding the IP address/LAN ID map  1524 , a storage device holding the LAN ID/router ID map  1526 , and a storage device holding the router ID/locator map  1528 . The location management server  1522  searches the IP address/LAN ID map  1524 , LAN ID/router ID map  1526 , and router ID/locator map  1528 , thereby acquiring locators correlated with destination IP addresses included in locator resolution requests received from the routers, and transmits response message including the acquired locators (locator resolution responses) to the source routers of the locator resolution requests. Note that the IP address/LAN ID map  1524 , LAN ID/router ID map  1526 , and router ID/locator map  1528  may be held in a single storage device. 
     The IP address/LAN ID map  1524  is a table representing the relation between the IP addresses of the interfaces of the communication devices coupled to the network  316 , and the identification information of the corresponding LANs (LAN ID). As illustrated in  FIG. 17 , the IP address “192.168.1.1” of the interface of the communication device  304  and the LAN ID “L1” of the LAN  308  are correlated, and the IP address “192.168.2.2” of the interface of the communication device  306  and the LAN ID “L2” of the LAN  310  are correlated. That is to say, two different LANs  308  and  310  are correlated as to the interfaces of the two communication device  304  and  306  belonging to the same logical network  302 . 
     The LAN ID/router ID map  1526  is a table indicating the relation between the identification information of each LAN (LAN ID) and the identification information of the routers coupled to the LANs (router ID). As illustrated in  FIG. 18 , the LAN ID “L1” of the LAN  308  and the router ID “R1” of the router  312  are correlated, and the LAN ID “L2” of the LAN  310  and the two router IDs “R2” and “R3” of the routers  1514  and  1542  coupled to the network  316  are correlated. That is to say, with the LAN  310 , two different routers  1514  and  1542  are correlated to a single LAN. 
     The router ID/locator map  1528  is a table indicating the relation between the identification information of each router coupled to the network  316  (router ID) and corresponding locators. As illustrated in  FIG. 19 , the router ID “R1” of the router  312  and the two locators “10.1.1.1” and “10.1.2.1” of the router  312  are correlated, the router ID “R2” of the router  1514  and the two locators “10.2.1.1” and “10.2.2.1” of the router  1514  are correlated, and the router ID “R3” of the router  1542  and the locator “10.3.1.1” of the router  1542  are correlated. That is to say, With the routers  312  and  1514 , two locators are correlated to one router ID. 
     4-2. Communication Control Method with Communication System  1500   
     The communication control method with the communication system  1500  differs from the communication control method of the communication system  300  illustrated in  FIG. 7  with regard to the locator acquisition processing executed in step S 706  and step S 714 , but other parts are the same. 
     The locator acquisition processing with the communication system  1500  differs from the locator acquisition processing with the communication system  300  with regard to the point that, at the time of acquiring a locator correlated with a destination IP address included in the locator resolution request, the three tables of the IP address/LAN ID map  1524 , LAN ID/router ID map  1526 , and router ID/locator map  1528  are used, instead of using the two tables of the IP address/router ID map  326  and router ID/locator map  328 , but other parts are the same. 
     Unlike the location management server  322 , in steps S 706  and S 714 , the location management server  1522  acquires a LAN ID correlated with the destination IP address included in the received locator resolution request, by searching the IP address/LAN ID map  1524 . In the examples illustrated in  FIGS. 7 and 15 , the destination IP address is “192.168.2.2”, and according to the map illustrated in  FIG. 17 , the acquired LAN ID is “L2”. 
     Further, the location management server  1522  acquires a router ID correlated with the acquired LAN ID, by searching the LAN ID/router ID map  1526 . In the examples illustrated in  FIGS. 7 and 15 , the LAN ID is “L2”, and according to the map illustrated in  FIG. 18 , the acquired router IDs are “R2” and “R3” 
     Further, the location management server  1522  acquires locators correlated with the acquired router IDs, by searching the router ID/locator map  1528 . In the examples illustrated in  FIGS. 7 and 15 , the router IDs are “R2” and “R3”, and according to the map illustrated in  FIG. 19 , the acquired locators are “10.2.1.1”, “10.2.2.1”, and “10.3.1.1”. 
     As described above, the location management server  1522  acquires locators correlated to destination IP addresses included in locator resolution requests received from the router  312 , in accordance with the above-described locator acquisition processing. The location management server  1522  transmits a response message including the acquired locators (locator resolution response) to the router  312 . In the examples illustrated in  FIGS. 7 and 15 , the three locators of “10.2.1.1”, “10.2.2.1”, and “10.3.1.1” are acquired as to the destination IP address 192.168.2.2. The destinations which the acquired locators indicate are three of the interfaces of the routers  1514  and  1542  to which the communication device  306  is coupled, so the locator resolution response includes “10.2.1.1”, “10.2.2.1”, and “10.3.1.1” as locators. 
     In step S 708 , the router  312  checks whether or not the locators included in the locator resolution response received from the location management server  1522  are included in the locator list  332 . In response to the locators included in the locator resolution response not being included in its own locator list  332 , in step S 710  the router  312  performs Proxy MAC address response processing as to the communication device  304  by a MAC address resolution response including the MAC address of its own interface. 
     As described above, even in a case where packet communication is performed between communication devices belonging to different LANs with a communication system where one logical network is configured of multiple LANs, with the communication system  1200  the router  312  to which the communication device  304  which has transmitted a MAC address resolution response is coupled executes Proxy MAC address response processing as to the communication device  304 , so packet communication may be executed in a normal manner. 
     Also, with the communication system  1500 , at the time of the router  312  deciding whether or not to execute Proxy MAC address response processing, the maps (location information)  1524 ,  1526 , and  1528 , indicating the relation between IP addresses and locators, held in the location management server  1522  which operates based on LISP, are used. Accordingly, a database relating to location information of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     4-3. Configuration of Routers  1514  and  1542   
     The configuration of the routers  1514  and  1542  in the communication system  1500  is the same as with the configuration of the routers  312  and  314  in the communication system  300 . Accordingly, detailed description will be omitted. 
     4-4. Configuration of Location Management server  1522   
       FIG. 20  is a functional block diagram illustrating the configuration of the location management server  1522  according to the third embodiment. 
     The location management server  1522  illustrated in  FIG. 20  differs from the location management server  322  illustrated in  FIG. 10  with regard to the point that a locator resolution request processing unit  2006  is provided instead of the locator resolution request processing unit  1006 , a LAN ID searching unit  2008 , an IP address/LAN ID map  2010 , a router ID searching unit  2012 , a LAN ID/router ID map  2014 , a locator searching unit  2016 , and an ID locator table  2018 , are provided instead of the router ID searching unit  1008 , IP address/router ID map  1010 , locator searching unit  1012 , and router ID/locator map  1014 , but other parts are the same. Parts which are the same as or equivalent to those in the location management server  322  illustrated in  FIG. 10  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 20  are the same as described with reference to  FIG. 10 , so detailed description will be omitted. 
     With the functional block diagram illustrated in  FIG. 20 , in the same way as with the functional block diagram illustrated in  FIG. 10 , portions of the location management server  1522  which correspond to functions relating to the Proxy MAC address response processing and locator resolution processing described with reference to  FIG. 7  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. 
     The locator resolution request processing unit  2006  receives locator resolution requests from the message identification unit  1004 , and notifies the information of the destination IP address included in the received locator resolution request to the LAN ID searching unit  2008 . 
     The LAN ID searching unit  2008  receives the information of the destination IP address from the locator resolution request processing unit  2006 , and searches the IP address/LAN ID map  2010  based on the received destination IP address, thereby acquiring the LAN ID correlated with that destination IP address (destination LAN ID). The LAN ID searching unit  2008  notifies the information of the acquired destination LAN ID to the locator resolution request processing unit  2006 . Note that the IP address/LAN IP map  2010  is the same as the IP address/LAN ID map  1524  illustrated in  FIG. 15 . 
     The locator resolution request processing unit  2006  acquires information of the destination LAN ID from the LAN ID searching unit  2008 , and notifies information of the acquired LAN ID to the router ID searching unit  2012 . 
     The router ID searching unit  2012  receives the information of the destination LAN ID from the locator resolution request processing unit  2006 , and searches the LAN ID/router ID map  2014  based on the received destination LAN ID, thereby acquiring the router ID correlated to that destination LAN ID (destination router ID). The router ID searching unit  2012  notifies the information of the acquired destination router ID to the locator resolution request processing unit  2006 . The LAN ID/router ID map  2014  is the same as the LAN ID/router ID map  1526  illustrated in  FIG. 15 . 
     The locator resolution request processing unit  2006  acquires information of the destination router ID from the router ID searching unit  2012 , and notifies the information of the acquired destination router ID to the locator searching unit  2016 . 
     The locator searching unit  2016  receives the information of the destination router ID from the locator resolution request processing unit  2006 , and searches the router ID/locator map  2018  based on the received destination router ID, thereby acquiring a locator correlated with the destination router ID (destination locator). The locator searching unit  2016  notifies the information of the acquired destination locator to the locator resolution request processing unit  2006 . Note that the router ID/locator map  2018  is the same as the router ID/locator map  1528  illustrated in  FIG. 15 . 
     The locator resolution request processing unit  2006  acquires information of the destination locator from the locator searching unit  2016 . The locator resolution request processing unit  2006  notifies the locator resolution response generating unit  1016  of the information of the acquired destination locator, in addition to the destination IP address. 
     Note that the hardware configuration of the location management server  1222  is the same as the hardware configuration of the location management server  322  illustrated in  FIG. 11 . The functions of the functional blocks of the location management server  1222  may be realized with the same hardware configuration of the location management server  322  illustrated in  FIG. 11 . The IP address/LAN ID map  2010 , LAN ID/router ID map  2014 , and router ID/locator map  2018 , are each stored in memory or a storage device. Accordingly, detailed description will be omitted. 
     As described above, at the time of the router  312  ( 314 ) deciding whether or not to execute Proxy MAC address response processing, the location management server  1522  operating based on LISP acquires the destination locator using the maps (location information)  1524 ,  1526 , and  1528 , representing the relation between IP addresses and locators, which it holds itself, and notifies the information of the acquired destination locators to the router  312  ( 314 ). Accordingly, a database relating to location information of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     5. Fourth Embodiment 
     The following is a description of a communication system, communication control method, relay device, and information processing device, according to a fourth embodiment. 
     5-1. Configuration of Communication System  2100   
       FIG. 21  is a diagram illustrating the configuration of a communication system  2100  according to the fourth embodiment.  FIG. 22  is a diagram illustrating an example of an IP address/locator cache map  2152 . 
     The communication system  2100  illustrated in  FIG. 21  differs from the communication system  300  illustrated in  FIG. 3  with regard to the points that routers  2112  and  2114  are provided instead of the routers  312  and  314 , and that IP address/locator cache maps  2152  and  2154  are added, and parts other than the above points are the same as with the communication system  300 . Parts which are the same as or equivalent to those in the communication system  300  illustrated in  FIG. 3  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 21  are the same as described with reference to  FIG. 3 , so detailed description will be omitted. 
     In  FIG. 21 , the router  2112  has, in the same way as with the router  312  illustrated in  FIG. 3 , an interface coupled to the communication device  304  via the LAN  308 , and two interfaces coupled to the network  316 . The router  2112  includes a storage device holding the locator list  332 . The router  2112  is a relay devices which relays packet communication between the communication device  304  and the network  316 , and operates based on the above-described LISP. 
     In the same way as with the router  312 , upon receiving a MAC address resolution request from a communication device belonging to the corresponding LAN  308 , the router  2112  transmits a locator resolution request to the location management server  322 , and thereafter receives a locator resolution response corresponding to that locator resolution request, from the location management server  322 . In the event that the destination locator included in the received locator resolution request is not included in the locator list  332 , the router  2112  performs Proxy MAC address response processing as to the source communication device using the MAC address of an interface of itself. 
     The router  2112  further includes a storage device holding the IP address/locator cache map  2152 . The IP address/locator cache map  2152  is a table holding information of destination IP addresses and destination locators included in a received locator resolution response, when the router  2112  receives a locator resolution response from the location management server  322 . In the example illustrated in  FIG. 22 , the IP address/locator cache map  2152  holds an entry indicating the relation between the IP address “192.168.2.2” (IP address of the interface of the communication device  306 ) and the corresponding locator “10.2.1.1” (IP address of the interface of the router  2114 ). 
     In the same way as with the router  314 , the router  2114  has an interface coupled to the communication device  306  via the LAN  310 , and an interface coupled to the network  316 . The router  2114  includes a storage device holding the locator list  334 . The router  2114  is a relay devices which relays packet communication between the communication device  306  and the network  316 , and operates based on the above-described LISP. 
     Upon receiving a MAC address resolution request from a communication device belonging to the corresponding LAN  310 , the router  2114  transmits a locator resolution request to the location management server  322 , and thereafter receives a locator resolution response corresponding to that resolution request, from the location management server  322 . In the event that the destination locator included in the received locator resolution request is not included in the locator list  334 , the router  2114  performs Proxy MAC address response processing as to the source communication device using the MAC address of an interface of itself. 
     The router  2114  further includes a storage device holding the IP address/locator cache map  2154 . The IP address/locator cache map  2154  is a storage table holding information of destination IP addresses and destination locators included in a received locator resolution response, when the router  2114  receives a locator resolution response from the location management server  322 . 
     Note that the IP address/locator cache maps  2152  and  2154  may each be held in a single storage device, or may be held spanning multiple storage devices. 
     5-2. Communication Control Method with Communication System  2100   
       FIG. 23  is a sequence chart for describing a communication control method with the communication system  2100 . Hereinafter, description will be made referencing  FIG. 21  in addition to  FIG. 23 , regarding a communication control method with the communication system  2100  in a case of transmitting packets from the interface of the communication device  304  to the interface of the communication device  306  belonging to the same logical network. 
     The communication control method illustrated in  FIG. 23  differs from the communication control method illustrated in  FIG. 7  with regard to the point that processing of steps S 2304  and S 2308  is performed instead of the processing of steps S 704  and S 708 , but processing other than these steps is the same as the communication control method illustrated in  FIG. 7 . Portions which are the same as or equivalent to those in the communication control method illustrated in  FIG. 7  are denoted with the same reference numerals. The operations and functions of the portions denoted by the same reference numerals in  FIG. 23  are the same as described with reference to  FIG. 7 , so detailed description will be omitted. 
     As illustrated in  FIG. 23 , in step S 2304  the router  2112  receives a MAC address resolution request transmitted from the communication device  304  in step S 702 . At this time, before transmitting a message (locator resolution request) requesting a locator (destination locator) correlated with the destination IP address included in the received MAC address resolution request to the location management server  322 , the router  2112  searches the IP address/locator cache map  2152  illustrated in  FIG. 22 , and based on the destination IP address included in the received MAC address resolution request, checks whether or not the destination locator correlated to that destination IP address is included in the IP address/locator cache map  2152 . 
     In the event that the destination locator is included in the IP address/locator cache map  2152 , the router  2112  references the IP address/locator cache map  2152 , thereby acquiring the destination locator correlated with the destination IP address. With the example illustrated in  FIGS. 21 and 23 , the IP address of the interface of the communication device  306  (destination IP address) is “192.168.2.2”, and according to the table illustrated in  FIG. 22 , the acquired destination locator is “10.2.1.1”. 
     On the other hand, in the event that the destination locator is not included in the IP address/locator cache map  2152 , the router  2112  transmits a message requesting the destination locator (locator resolution request) to the location management server  322 , in the same way as with step S 704 . In the same way as with step S 706 , the router  2112  acquires the destination locator correlated with the destination IP address by receiving a locator resolution response corresponding to that locator resolution request from the location management server  322 . 
     Note that in the event that multiple locators are assigned to the router coupled to the interface of the destination communication device  306 , or in the event that the interface of the destination communication device  306  is coupled to multiple routers, unlike the example illustrated in  FIG. 21 , multiple locators are correlated with a single IP address in the IP address/locator cache map  2152 , unlike the example illustrated in  FIG. 22 . In this case, the router  2112  acquires the multiple destination locators correlated with the destination IP address. 
     Next, in step S 708 , the router  2112  references the locator list  332 , so as to check whether or not the destination locator acquired in step S 2304  is included in its own locator list  332 . 
     With the example illustrated in  FIG. 21 , the router  2112  checks that the acquired destination locator “10.2.1.1” is not included in its own locator list  332 , based on the locator list  332  illustrated in  FIG. 4A . Accordingly, the router  2112  recognizes that the interface of the communication address  306  having this destination IP address does not belong to the LAN  308 . 
     In step S 710 , in response to the acquired destination locator not being included in its own locator list  332 , the router  2112  performs Proxy MAC address response processing as to the communication device  304  which has transmitted to the MAC address resolution request in step S 702 , by a MAC address proxy response including the MAC address of the interface of itself. 
     As described above, even in a case where packet communication is performed between communication devices belonging to different LANs with a communication system where one logical network is configured of multiple LANs, with the communication system  2100  the router  2112  to which the communication device  304  which has transmitted a MAC address resolution request is coupled executes Proxy MAC address response processing as to the communication device  304 , so packet communication may be executed in a normal manner. 
     Also, with the communication system  2100 , at the time of the router  2112  deciding whether or not to execute Proxy MAC address response processing, the cache map information (location information) of the IP address/locator cache map  2152  indicating the relation between IP addresses and locators, held in the router  2112 , is used. Accordingly, a database relating to location information of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. Also, in the event that cache map information (location information) of the IP address/locator cache map  2152  may be used, transmission/reception of a locator resolution request and a corresponding locator resolution response is not performed between the router  2112  and the location management server  322 , so the amount of communication between the router  2112  and the location management server  322  may be suppressed, thereby alleviating the communication load with regard to the network  316 . 
     5-3. Configuration of Router  2112  ( 2114 ) 
       FIG. 24  is a diagram illustrating the configuration of the router  2112  ( 2114 ) according to the fourth embodiment. 
     The router  2112  ( 2114 ) illustrated in  FIG. 24  differs from the router  312  ( 314 ) illustrated in  FIG. 8  with regard to the points that a locator resolution request generating unit  2410  and a locator resolution response processing unit  2416  are provided instead of the locator resolution request generating unit  810  and locator resolution response processing unit  816 , and that an IP address/locator cache map  2432  is provided but is the same as the router  312  ( 314 ) other than the above points. Parts which are the same as or equivalent to those in the router  312  ( 314 ) illustrated in  FIG. 8  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 24  are the same as described with reference to  FIG. 8 , so detailed description will be omitted. 
     With the functional block illustrated in  FIG. 24 , the portions corresponding to the functions of the router  2112  ( 2114 ) relating to the Proxy MAC address response processing described with reference to  FIG. 23  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. Also, while the configuration of the router  2112  will be described, the router  2112  and  2114  have mutually equivalent configurations in the communication system  2100 . 
     As illustrated in  FIG. 24 , the locator resolution request generating unit  2410  receives information of a destination IP address from the MAC address resolution request processing unit  806 . The locator resolution request generating unit  2410  searches the IP address/locator cache map  2432  based on the information of that destination IP address, and checks whether or not the destination locator correlated to that destination IP address is included in the IP address/locator cache map  2432 . Note that the IP address/locator cache map  2432  is the same as the IP address/locator cache map  2152  ( 2154 ) illustrated in  FIG. 21 . 
     In the event that the destination locator is included in the IP address/locator cache map  2432 , the locator resolution request generating unit  2410  references the IP address/locator cache map  2432 , so as to acquire the destination locator correlated with the destination IP address. The locator resolution request generating unit  2410  outputs the destination IP address included in the MAC address resolution request and cache map hit information including the acquired destination locator to the locator resolution response processing unit  2416 . At this time, the locator resolution request generating unit  2410  does not generate a locator resolution request. 
     On the other hand, in the event that the destination locator is not included in the IP address/locator cache map  2432 , the locator resolution request generating unit  2410  generates a locator resolution request including the destination IP address based on the received destination IP address. The locator resolution request generating unit  2410  outputs the generated locator resolution request to the transmission/reception unit  812 . 
     In the event of having received cache map hit information from the MAC address resolution request processing unit  806 , the locator resolution response processing unit  2416  acquires information of the destination IP address and destination locator from the received cache map hit information. In the other hand, in the event of having received a locator resolution request from the message identification unit  814 , the locator resolution response processing unit  2416  acquires information of the destination IP address and destination locator from the received locator resolution request. 
     The locator resolution response processing unit  2416  references the locator list  818 , thereby checking whether or not the acquired destination locator is included in the locator list  818 . Now, the locator list  818  is the same as the locator list  332  ( 334 ) illustrated in  FIG. 3 . 
     In the event that the destination locator is not included in the locator list  818 , the locator resolution response processing unit  2416  notifies the MAC address resolution request generating unit  820  to that effect, and also outputs the destination IP address included in the received locator resolution response to the MAC address proxy response generating unit  820 . 
     Note that the hardware configuration of the router  2112  ( 2114 ) is the same as the hardware configuration of the router  312  ( 314 ) illustrated in  FIG. 9 . The functions of the functional blocks of the router  2112  ( 2114 ) may be realized with the same hardware configuration of the router  312  ( 314 ) illustrated in  FIG. 9 . The IP address/locator cache map  2432  is stored in memory or a storage device. Accordingly, detailed description will be omitted. 
     As described above, even in a case where packet communication is performed between communication devices  304  and  306  belonging to different LANs, the router  2112  to which the communication device  304  which has transmitted a MAC address resolution response is coupled executes Proxy MAC address response processing as to the communication device  304 , so packet communication may be executed in a normal manner. 
     Also, at the time of the router  2112  deciding whether or not to execute Proxy MAC address response processing, the cache map information (location information) of the IP address/locator cache map  2152  indicating the relation between IP addresses and locators, held in the router  2112  itself, is used. Accordingly, a database relating to location information of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. Also, in the event that cache map information (location information) of the IP address/locator cache map  2152  may be used, transmission/reception of a locator resolution request and a corresponding locator resolution response is not performed between the router  2112  and the location management server  322 , so the amount of communication with the location management server  322  may be suppressed, thereby alleviating the communication load with regard to the network  316 . 
     5-4. Configuration of Location Management Server  322   
     The configuration of the location management server  322  in the communication system  2100  is the same as the configuration of the location management server  322  in the communication system  300 . Accordingly, detailed description will be omitted. 
     6. Fifth Embodiment 
     The following is a description of a communication system and communication control method, according to a fifth embodiment. 
     6-1. Configuration of Communication System  2500   
       FIG. 25  is a diagram illustrating the configuration of a communication system  2500  according to a fifth embodiment, and  FIGS. 26A through 26C  are diagrams illustrating an example of IP address/MAC address cache maps  2552  through  2556  before changing of a LAN to which a communication device  2554  is coupled. 
     The communication system  2500  illustrated in  FIG. 25  differs from the communication system  300  illustrated in  FIG. 3  with regard to the points that communication devices  2504 ,  2506 , and  2544  are provided instead of the communication devices  302  and  304 , and that IP address/MAC address cache maps  2552  through  2560  are added, and parts other than the above points are the same as with the communication system  300 . Parts which are the same as or equivalent to those in the communication system  300  illustrated in  FIG. 3  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 25  are the same as described with reference to  FIG. 3 , so detailed description will be omitted. 
     The communication device  2504  and communication device  2544  belong to the same logical network  302 , and further belong to the same LAN  308 . The communication devices  2504  and  2544  each are coupled to the network  316  via the corresponding router  312 . The communication device  2506  belongs to the same logical network  302  as the communication devices  2504  and  2544 , but belong to a different LAN. The communication device  2506  belongs to LAN  310 , and is coupled to the network  316  via the corresponding router  314 . 
     The communication device  2504  includes a storage device holding the IP address/MAC address cache map  2552 . The IP address/MAC address cache map  2552  is a cache map table holding information of destination IP addresses and destination MAC addresses included in a received MAC address resolution response, when the communication device  2504  receives a MAC address resolution response. In the event that the MAC address proxy response is an ARP response, an ARP cache map is held in the IP address/MAC address cache map  2552 . 
     With the example illustrated in  FIG. 26A , two entries are held in the IP address/MAC address cache map  2552 , which are the relation between the IP address “192.168.1.2” (IP address of the interface of the communication device  2544 ) and the corresponding MAC address “M2” (MAC address of the interface of the communication device  2544 ), and the relation between the IP address “192.168.2.2” (IP address of the interface of the communication device  2506 ) and the corresponding MAC address “MR1” (MAC address of the interface of the router  312 ). 
     Now, the reason why the MAC address “MR1” of the interface of the router  312  has been correlated with the IP address “192.168.2.2” of the interface of the communication device  2506  is in order for, since the communication device  2506  belongs to a different LAN  310  from the communication device  2504 , the router  312  to perform Proxy MAC address response processing as to the communication device  2504  by a MAC address resolution response including the MAC address “MR1” of its own device, when the communication device  2504  transmits a message requesting the MAC address of the interface of the communication device  2506  (MAC address resolution request). 
     In the same way as with the communication device  2504 , the communication device  2506  includes a storage device holding the IP address/MAC address cache map  2554 . The IP address/MAC address cache map  2554  is a cache map table holding information of destination IP addresses and destination MAC addresses included in a received MAC address resolution response, when the communication device  2506  receives a MAC address resolution response. In the event that the MAC address proxy response is an ARP response, an ARP cache map is held in the IP address/MAC address cache map  2554 . 
     With the example illustrated in  FIG. 26B , two entries are held in the IP address/MAC address cache map  2554 , which are the relation between the IP address “192.168.1.1” (IP address of the interface of the communication device  2504 ) and the corresponding MAC address “MR2” (MAC address of the interface of the router  314 ), and the relation between the IP address “192.168.1.2” (IP address of the interface of the communication device  2544 ) and the corresponding MAC address “MR2” (MAC address of the interface of the router  314 ). 
     Now, the reason why the MAC address “MR2” of the interface of the router  314  has been correlated with both IP addresses “192.168.1.1” and “192.168.1.2” of the interface of the communication device  2506  is in order for, since the communication devices  2504  and  2544  belong to a different LAN  308  from the communication device  2506 , the router  314  to perform Proxy MAC address response processing as to the communication device  2506  by a MAC address resolution response including the MAC address “MR2” of its own interface, when the communication device  2506  transmits a message requesting the MAC address of the interface of the communication device  2504  (MAC address resolution request). 
     The communication device  2544  includes a storage device holding the IP address/MAC address cache map  2556 . The IP address/MAC address cache map  2556  is a table holding information of destination IP addresses and destination MAC addresses included in a received MAC address resolution response, when the communication device  2544  receives a MAC address resolution response. 
     With the example illustrated in  FIG. 26C , two entries are held in the IP address/MAC address cache map  2556 , which are the relation between the IP address “192.168.1.1” (IP address of the interface of the communication device  2504 ) and the corresponding MAC address “M1” (MAC address of the interface of the communication device  2504 ), and the relation between the IP address “192.168.2.2” (IP address of the interface of the communication device  2506 ) and the corresponding MAC address “MR1” (MAC address of the interface of the router  312 ). 
     The routers  312  and  314  also include storage devices which store IP address/MAC address cache maps  2558  and  2560  in the same way. 
     6-2. Communication Control Method with Communication System  2500   
     Now, a communication control method will be described regarding a case where, with the communication system  2500  illustrated in  FIG. 25 , the communication device  2544  is switched from being coupled to the LAN  308  to a different LAN  310  within the same logical network  302 .  FIGS. 26A through 26C  are diagrams illustrating an example of IP address/MAC address cache maps  2552  through  2556  before changing of the LAN to which the communication device  2544  is coupled, and  FIGS. 27A through 27C  are diagrams illustrating an example of IP address/MAC address cache maps  2552  through  2556  after changing of the LAN to which the communication device  2544  is coupled; 
     In the event that the communication device  2544  is a virtual machine, moving of the communication device  2544  described above occurs when the communication device  2544  is moved from the server where it is currently situated to another server by live migration, for example. Also, the event that the communication device  2544  is a rack-mounted server, moving of the communication device  2544  described above occurs when the communication device  2544  is relocated from the rack where it is currently mounted to another rack, for example. 
     Before the LAN to which it is coupled is changed, the communication device  2544  broadcasts a message to all communication devices and routers belonging to the LAN  308  to which it is coupled, to invalidate entries corresponding to the IP address “192.168.1.2” of its own interface from their IP address/MAC address cache maps (entry invalidation request). 
     The communication device  2504  receives the above-described entry invalidation request from the communication device  2544  and invalidates the entry corresponding to the IP address “192.168.1.2” of the interface of the communication device  2544  from the entries in the IP address/MAC address cache map  2552 . Accordingly, as illustrated in  FIG. 27A , the IP address/MAC address cache map  2552  no longer includes an entry corresponding to the IP address “192.168.1.2” of the interface of the communication device  2544 . 
     At the IP address/MAC address cache map  2558  which the router  312  holds as well, the entry corresponding to the IP address “192.168.1.2” of the interface of the communication device  2544  is invalidated. 
     Further, after the LAN to which it is coupled is changed, the communication device  2544  broadcasts a message to all communication devices and routers belonging to the LAN  310  to which it has been coupled, to update entries corresponding to the IP address “192.168.1.2” of its own interface in their IP address/MAC address cache maps (entry update request). That is to say, the communication device  2544  requests updating of the entry corresponding to the IP address “192.168.1.2” (IP address of the interface of the communication device  2544 ), in each of the IP address/MAC address cache maps, so as to indicate the relation with the MAC address “M2” (MAC address of the interface of the communication device  2544 ). 
     The communication device  2506  receives the above-described entry update request from the communication device  2544  and updates the entry corresponding to the IP address “192.168.1.2” of the interface of the communication device  2544  in the entries in the IP address/MAC address cache map  2554 . Accordingly, as illustrated in  FIG. 27B , the IP address/MAC address cache map  2554  includes an entry indicating the relation between the IP address “192.168.1.2” of the interface of the communication device  2544  and the corresponding MAC address “M2” (MAC address of the interface of the communication device  2544 ). 
     At the IP address/MAC address cache map  2560  which the router  314  holds as well, the entry corresponding to the IP address “192.168.1.2” of the interface of the communication device  2544  is updated. 
     Further, after the LAN to which it is coupled is changed, the communication device  2544  invalidates all entries of the IP address/MAC address cache map  2556 . Accordingly, as illustrated in  FIG. 27C , the IP address/MAC address cache map  2556  becomes empty, with no entries included. 
     While the above embodiment has been described with an entry update request being transmitted by the communication device  2544  after the LAN to which it is coupled has been changed. An entry invalidation request may be transmitted instead. In this case, an entry corresponding to the IP address “192.168.1.2” (the IP address of the interface of the communication device  2544 ) is newly generated at the IP address/MAC address cache maps of each of the communication devices and routers belonging to the LAN  310 , by way of ARP request and ARP response processing. 
     As described above, with a communication system where one logical network is configured of multiple LANs, even in a case where the LAN to which a communication devices is coupled is changed to a different LAN, with the communication system  2500  cache map information (location information) of the IP address/MAC address cache maps  2552  through  2560  which the communication devices hold may be updated to suitable content, so malfunctioning in communication after the LAN to which the communication devices is coupled is changed may be avoided, thereby improving the stability of the communication system. 
     7. Sixth Embodiment 
     The following is a description of a communication system, communication control method, relay device, and information processing device, according to a sixth embodiment. 
     7-1. Configuration of Communication System  2800   
       FIG. 28  is a diagram illustrating the configuration of a communication system  2800  according to the sixth embodiment,  FIG. 29  is a diagram illustrating an example of a proxy MAC address response list  2862 , and  FIG. 30  is a diagram illustrating an example of an IP address/MAC address map  2824 . 
     The communication system  2800  illustrated in  FIG. 28  differs from the communication system  300  illustrated in  FIG. 3  with regard to the points that routers  2812  and  2814  are provided instead of the routers  312  and  314 , and that proxy MAC address response lists  2862  and  2864 , and an IP address/MAC address map  2824  are provided, and parts other than the above points are the same as with the communication system  300 . Parts illustrated which are the same as or equivalent to those in the communication system  300  illustrated in  FIG. 3  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 28  are the same as described with reference to  FIG. 3 , so detailed description will be omitted. 
     In  FIG. 28 , the router  2812  has, in the same way as with the router  312  illustrated in  FIG. 3 , an interface coupled to the communication device  304  via the LAN  308 , and two interfaces coupled to the network  316 . The router  2812  includes a storage device holding the locator list  332 . The router  2812  is a relay devices which relays packet communication between the communication device  304  and the network  316 , and operates based on the above-described LISP. 
     In the same way as with the router  312 , upon receiving a MAC address resolution request from a communication device belonging to the corresponding LAN  308 , the router  2812  transmits a locator resolution request to the location management server  2822 , and thereafter receives a locator resolution response corresponding to that resolution request, from the location management server. In the event that the destination locator included in the received locator resolution request is not included in the locator list  332 , the router  2812  generates a MAC address resolution response using the MAC address included in the locator resolution request, and performs Proxy MAC address response processing as to the source communication device by way of the generated MAC address resolution response. 
     The router  2812  further includes a storage device holding the proxy MAC address response list  2862 . The proxy MAC address response list  2862  is a table holding information of destination MAC addresses included in a received locator resolution response, when the router  2812  receives a locator resolution response from a location management server  2822 . With the communication system  2800  illustrated in  FIG. 28 , the locator resolution response which the location management server  2822  transmits includes information of the destination MAC address, in addition to the destination IP address and destination locator, unlike the case of the communication system  300  illustrated in  FIG. 3 . In the example illustrated in  FIG. 29 , the proxy MAC address response list  2862  holds an entry indicating the MAC address “M2” (MAC address of the interface of the communication device  306 ). 
     In the same way as with the router  314 , the router  2814  has an interface coupled to the communication device  306  via the LAN  310 , and an interface coupled to the network  316 . The router  2814  includes a storage device holding the locator list  334 . The router  2814  is a relay devices which relays packet communication between the communication device  306  and the network  316 , and operates based on the above-described LISP. 
     Upon receiving a MAC address resolution request from a communication device belonging to the corresponding LAN  310 , in the same way as with the router  314 , the router  2814  transmits a locator resolution request to the location management server  2822 , and thereafter receives a locator resolution response corresponding to that resolution request, from the location management server  2822 . In the event that the destination locator included in the received locator resolution request is not included in the locator list  334 , the router  2814  generates a MAC address resolution response using the MAC address included in the locator resolution request, and performs Proxy MAC address response processing as to the source communication device by way of the generated MAC address resolution response. 
     The router  2814  further includes a storage device holding the proxy MAC address response list  2864 . The proxy MAC address response list  2864  is a table holding information of destination MAC addresses included in a received locator resolution response, when the router  2814  receives a locator resolution response from the location management server  2822 . 
     Note that the proxy MAC address response lists  2862  and  2864  may each be held in a single storage device, or may be held spanning multiple storage devices. 
     The location management server  2822  is an information processing device coupled to the network  316  and operating based on LISP described above. The location management server  2822  includes a storage device holding the IP address/router ID map  326  and router ID/locator map  328 , in the same way as with the location management server  322  illustrated in  FIG. 3 . The location management server  2822  searches the IP address/router ID map  326  and the router ID/locator map  328 , thereby acquiring locators correlated with destination IP addresses included in locator resolution requests received from the routers (destination locators). 
     The location management server  2822  further includes a storage device holding an IP address/MAC address map  2824 . The IP address/MAC address map  2824  is a table representing the relation between IP addresses and MAC addresses of the communication devices coupled to the network  316  via corresponding routers. As illustrated in  FIG. 30 , the IP address “192.168.1.1” of the interface of the communication device  304  and the corresponding MAC address “M1” are correlated, and the IP address “192.168.2.2” of the interface of the communication device  306  and the corresponding MAC address “M2” are correlated. 
     That is to say, with the communication system  2800  illustrated in  FIG. 28 , the location management server  2822  holds information indicating the correlation between the IP addresses and MAC addresses of the communication devices coupled to the network to which it is coupled. Note that the IP address/MAC address map  2824  may be held in a single storage device, or may be held spanning multiple storage devices. 
     The location management server  2822  searches the IP address/MAC address map  2824 , thereby acquiring MAC addresses correlated with destination IP addresses included in locator resolution requests received from the routers (destination MAC addresses). The location management server  2822  transmits a response message including the acquired destination locator and destination MAC address (locator resolution response) to the source router of the locator resolution request. 
     7-2. Communication Control Method with Communication System  2800   
       FIG. 31  is a sequence chart for describing a communication control method with the communication system  2800 . Hereinafter, description will be made referencing  FIG. 28  in addition to  FIG. 31 , regarding a communication control method with the communication system  2800  in a case of transmitting packets from the interface of the communication device  304  to the interface of the communication device  306  belonging to the same logical network. 
     The communication control method illustrated in  FIG. 31  differs from the communication control method illustrated in  FIG. 7  with regard to the point that processing of step S 3106  is performed instead of the processing of step S 706 , and processing of steps S 3110 , S 3122 , S 3112 , and S 3124  is performed instead of the processing of steps S 710  and S 712 , but processing other than these steps is the same as the communication control method illustrated in  FIG. 7 . Portions which are the same as or equivalent to those in the communication control method illustrated in  FIG. 7  are denoted with the same reference numerals. The operations and functions of the portions denoted by the same reference numerals in  FIG. 31  are the same as described with reference to  FIG. 7 , so detailed description will be omitted. 
     As illustrated in  FIG. 31 , in step S 3106  the location management server  2822  receives a locator resolution request from the router  2812 . 
     The location management server  2822  searches the IP address/router ID map  326  based on the destination IP address included in the received locator resolution request, thereby acquiring identification information of the router correlated to that destination IP address (router ID). Further, the location management server  2822  searches the router ID/locator map  328  that is held, based on the acquired router ID, thereby acquiring the locator correlated with the acquired router ID. 
     The location management server  2822  acquires the destination locator correlate with the destination IP address included in the locator resolution request received from the router  312 , by the above-described locator acquisition processing. In the example illustrated in  FIGS. 28 and 31 , one locator “10.2.1.1” is acquired as to the destination IP address “192.168.2.2”. 
     Note that unlike the example illustrated in  FIG. 28 , in a case where multiple locators are assigned to the router coupled to the interface of the destination communication device  306 , or in the event that the interface of the destination communication device  306  is coupled to multiple routers, multiple locators are correlated with a single IP address included in the locator resolution request, and the location management server  2822  transmits a locator resolution response including multiple locators. 
     Further, the location management server  2822  searches the IP address/MAC address map  2824  that is held, based on the destination IP address included in the received locator resolution request, thereby acquiring the MAC address of the interface of the destination communication device having that destination IP address (destination MAC address). With the example illustrated in  FIGS. 28 and 31 , the destination IP address is “192.168.2.2”, and according to the map illustrated in  FIG. 30 , the acquired destination MAC address is “M2”. 
     The location management server  2822  transmits a response message including the acquired destination locator and destination MAC address (locator resolution response) to the router  2812 . 
     Next, in step S 708 , the router  2812  references the locator list  332 , so as to check whether or not the destination locator included in the locator resolution response received from the location management server  2822  is included in its own locator list  332 . 
     With the example illustrated in  FIG. 28 , the router  2812  checks that the destination locator “10.2.1.1” included in the locator resolution response is not included in the locator list  332 , and recognizes that the interface of the communication address  306  having this destination IP address does not belong to the LAN  308 . 
     Next, in step S 3110 , in response to the acquired destination locator included in the locator resolution response not being included in the locator list  332 , the router  2812  transmits a response message as to the MAC address resolution request (MAC address resolution response) to the communication device  304 . 
     At this time, the router  2812  appends the destination MAC address “M2” which is included in the locator resolution response to the MAC address resolution response. That is to say, the router  2812  uses the MAC address of the interface of the communication device  306  to generate a response message (MAC address resolution response), as a proxy for the communication device  306  which originally ought to respond to the MAC address resolution request, and performs Proxy MAC address response processing with the generated MAC address resolution response. 
     By recognizing that the interface of the communication device  306  does not belong to the LAN  308 , the router  2812  recognizes that in the current state, the communication device  304  which has transmitted the MAC address resolution request will not receive a corresponding MAC address resolution response, and accordingly will not recognize the MAC address of the interface of the communication device  306 . Accordingly, the router  312  executes the above-described Proxy MAC address response processing with regard to the communication device  304 , so as to avoid a situation in which packet transmission from the communication device  304  to the interface of the communication device  306  is not started. 
     Next, in step S 3122 , the router  2812  updates the proxy MAC address response list  2862  in accordance with the destination MAC address included in the received MAC address resolution response. In the event that the destination MAC address included in the received MAC address resolution response is not included in the proxy MAC address response list  2862 , the router  2812  adds the value of that destination MAC address to the proxy MAC address response list  2862 . In the example illustrated in  FIG. 28 , the destination MAC address is “M2”, and as illustrated in  FIG. 29 , the MAC address “M2” is added to the proxy MAC address response list  2862  which is an empty state. 
     Next, in step S 3112 , the communication device  304  receives a MAC address resolution response from the router  2812 . The communication device  304  recognizes the MAC address of the interface of the communication device  306  (“M2” in the example illustrated in  FIG. 28 ) that is included in the received MAC address resolution response as being the MAC address which is the destination (destination MAC address). The communication device  304  transmits a packet of which the destination is the interface of the communication device  306 , as a frame with the interface of the communication device  306  as the destination thereof. At this time, the transmitted frame includes the IP address of the destination communication device  306  interface as the destination IP address, and also includes the MAC address and IP address of the interface of the destination communication device  306  as the destination MAC address. With the example illustrated in  FIG. 28 , the transmitted frame includes “192.168.2.2” as the destination IP address and also includes “M2” as the destination MAC address. 
     Next, in step S 3124 , the router  2812  checks the destination MAC address included in the frame transmitted from the communication device  304 . The router  2812  references the proxy MAC address response list  2862  that is held, thereby checking whether or not the destination MAC address included in the frame transmitted from the communication device  304  is included in its own proxy MAC address response list  2862 . 
     In the example illustrated in  FIG. 28 , the router  2812  checks that the destination MAC address “M2” included in the frame is included in the proxy MAC address response list  2862 , based on the proxy MAC address response list  2862  illustrated in  FIG. 29 . Accordingly, the router  2812  recognizes that this frame has been transmitted from the router  2812  itself to the communication device which has performed the Proxy MAC address response processing in step S 3110 . 
     In the event that the destination MAC address included in the frame is included in the proxy MAC address response list  2862 , the router  2812  decides to receive that frame. The router  2812  extracts the packet from the received frame, and transmits to the location management server  2822  a message requesting the locator correlated with the destination IP address included in the extracted packet (locator resolution request). 
     The router  2812  recognizes that the communication device  306  which has performed the MAC address resolution response in proxy does not belong to the LAN  308 , and accordingly recognizes that in the current state the frame transmitted from the communication device  304  will not be revived by any device. Accordingly, in order to avoid a situation in which the frame does not reach the interface of the communication device  306  which is the destination thereof, the router  312  receives the frame transmitted from the communication device  304 , and transmits a locator resolution request described above to the location management server  2822 . 
     Next, in step S 714 , the router  2812  receives the frame from the communication device  304 . The router  2812  and location management server  2822  use the destination IP address included in the received frame, i.e., the IP address of the interface of the communication device  306 , to execute locator resolution processing. 
     As described above, even in a case where packet communication is performed between communication devices belonging to different LANs with a communication system where one logical network is configured of multiple LANs, with the communication system  2800  the router  2812  to which the communication device  304  which has transmitted a MAC address resolution request is coupled executes Proxy MAC address response processing as to the communication device  304  using the MAC address of the destination communication device  306 , so packet communication may be executed in a normal manner. 
     7-3. Configuration of Router  2812  ( 2814 ) 
       FIG. 32  is a diagram illustrating the configuration of the router  2812  ( 2814 ) according to the sixth embodiment. 
     The router  2812  ( 2814 ) illustrated in  FIG. 32  differs from the router  312  ( 314 ) illustrated in  FIG. 8  with regard to the points that a locator resolution response processing unit  3216  and a MAC address resolution response generating unit  3220  are provided instead of the locator resolution response processing unit  820  and MAC address resolution response generating unit  820 , and that a proxy MAC address response list  3234  is provided, but is the same as the router  312  ( 314 ) other than the above points. Parts which are the same as or equivalent to those in the router  312  ( 314 ) illustrated in  FIG. 8  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 32  are the same as described with reference to  FIG. 8 , so detailed description will be omitted. 
     With the functional block illustrated in  FIG. 32 , the portions corresponding to the functions of the router  2812  ( 2814 ) relating to the Proxy MAC address response processing described with reference to  FIG. 31  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. Also, while the configuration of the router  2812  will be described, the router  2812  and  2814  have mutually equivalent configurations in the communication system  2800 . 
     As illustrated in  FIG. 32 , the locator resolution response processing unit  3216  receives a locator resolution response from the message identification unit  814 . The received locator resolution response includes a destination IP address (IP address of the interface of the destination communication device), destination MAC address (MAC address of the interface of the destination communication device), and destination locator (IP address of the interface of the packet destination router). 
     The locator resolution response processing unit  3216  acquires the information of the destination locator included in the received locator resolution response. By referencing the locator list  818 , the locator resolution response processing unit  3216  checks whether or not the acquired destination locator is included in the locator list  818 . Note that the locator list  818  is the same as the locator list  332  ( 334 ) illustrated in  FIG. 3 . 
     In the event that the destination locator is not included in the locator list  818 , the locator resolution response processing unit  3216  notifies the MAC address resolution response generating unit  3220  to that effect, and outputs the destination IP address included in the received locator resolution response to the MAC address resolution response generating unit  3220 . 
     The MAC address resolution response generating unit  3220  acquires the destination IP address and destination MAC address from the locator resolution response processing unit  3216 . Based on the acquired destination IP address, the locator resolution response processing unit  3216  reads out the corresponding source MAC address (MAC address of the interface of the communication device which is the source of the MAC address resolution request) from the MAC address resolution request reception table  808 . 
     In the event that the destination locator is not included in the locator list  818 , the MAC address resolution response generating unit  3220  further references the proxy MAC address response list  3234 , thereby checking whether or not the acquired destination MAC address is included in the proxy MAC address response list  3234 . Note that the proxy MAC address response list  3234  is the same as the proxy MAC address response list  2862  ( 2864 ) illustrated in  FIG. 28 . 
     In the event that the acquired destination MAC address is included in the proxy MAC address response list  3234 , the MAC address resolution response generating unit  3220  generates a MAC address resolution response, based on the acquired destination IP address and the source MAC address. That is to say, the MAC address resolution response generating unit  3220  generates a MAC address resolution response including the destination MAC address, in addition to the destination IP address and source MAC address. The MAC address resolution response generating unit  3220  outputs the generated MAC address resolution response to the transmission/reception unit  802 . 
     Note that the hardware configuration of the router  2812  ( 2814 ) is the same as the hardware configuration of the router  312  ( 314 ) illustrated in  FIG. 9 . The functions of the functional blocks of the router  2812  ( 2814 ) may be realized by the same hardware configuration as the hardware configuration of the router  312  ( 314 ) illustrated in  FIG. 9 . The proxy MAC address response list  3234  is stored in memory or a storage device. Accordingly, detailed description will be omitted. 
     As described above, even in a case where packet communication is performed between communication devices belonging to different LANs with a communication system where one logical network is configured of multiple LANs, the router  2812  to which the communication device  304  which has transmitted a MAC address resolution request is coupled executes Proxy MAC address response processing as to the communication device  304  using the MAC address of the destination communication device, so packet communication may be executed in a normal manner. 
     7-4. Configuration of Location Management Server  2822   
       FIG. 33  is a functional block diagram illustrating the configuration of the location management server  2822  according to the sixth embodiment. 
     The location management server  2822  illustrated in  FIG. 33  differs from the location management server  322  illustrated in  FIG. 10  with regard to the point that a locator resolution request processing unit  3306  and locator resolution response generating unit  3316  are provided instead of the locator resolution request processing unit  1006  and locator resolution response generating unit  1016 , and a MAC address searching unit  3322  and IP address/MAC address map  3324  have been added, but other parts are the same. Parts which are the same as or equivalent to those in the location management server  322  illustrated in  FIG. 10  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 33  are the same as described with reference to  FIG. 10 , so detailed description will be omitted. 
     With the functional block diagram illustrated in  FIG. 33 , in the same way as with the functional block diagram illustrated in  FIG. 10  portions of the location management server  2822  which correspond to functions relating to the Proxy MAC address response processing and locator resolution processing described with reference to  FIG. 31  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. 
     The locator resolution request processing unit  3306  receives a locator resolution request from the message identification unit  1004  in the same way as with the locator resolution request processing unit  1006  illustrated in  FIG. 10 , and notifies information of the destination IP address included in the received locator resolution request to the router ID searching unit  1008 , thereby acquiring the information of the destination router ID correlated with the destination IP address. The locator resolution request processing unit  3306  notifies the information of the acquired destination router ID to the locator searching unit  1012 , thereby acquiring information of the destination locator correlated to the destination router ID from the locator searching unit  1012 . 
     The locator resolution request processing unit  3306  further notifies the information of the destination IP address included in the received locator resolution request to the MAC address searching unit  3322 . 
     The MAC address searching unit  3322  receives the information of the destination IP address from the locator resolution request processing unit  3306 , and searches the IP address/MAC address map  3324  based on the received destination IP address, thereby acquiring the MAC address correlated with that destination IP address (destination MAC address). The MAC address searching unit  3322  notifies the information of the acquired destination MAC address to the locator resolution request processing unit  3306 . Note that the IP address/MAC address map  3324  is the same as the IP address/MAC address map  2824  illustrated in  FIG. 28 . 
     In addition to the destination IP address, the locator resolution request processing unit  3306  notifies the information of the acquired destination locator and destination MAC address to the locator resolution response generating unit  3316 . 
     The locator resolution response generating unit  3316  receives the information of the destination IP address, destination locator, and destination MAC address from the locator resolution request processing unit  3306 , and generates a locator resolution response including the received destination IP address, destination locator, and destination MAC address. The locator resolution response generating unit  3316  outputs the generated locator resolution response to the transmission/reception unit  1002 . 
     Note that the hardware configuration of the location management server  2822  is the same as the hardware configuration of the location management server  322  illustrated in  FIG. 11 . The functions of the functional blocks of the location management server  2822  may be realized with the same hardware configuration of the location management server  322  illustrated in  FIG. 11 . The IP address/MAC address map  3324  illustrated in  FIG. 33  is stored in memory or a storage device. Accordingly, detailed description will be omitted. 
     As described above, with the communication system  2800 , at the time of the router  2812  deciding whether or not to execute Proxy MAC address response processing, the location management server  2822  operating based on LISP notifies the MAC address of the destination communication device  306  to the router  2812 , using the maps (location information)  326 ,  328 , and  2824 , representing the relation between IP addresses, locators, and MAC addresses, which the location management server  2822  itself holds. Accordingly, a database relating to location information of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     8. Seventh Embodiment 
     The following is a description of the communication system, communication method, relay device, and information processing device according to a seventh embodiment. 
     8-1. Configuration of Communication System  3400   
       FIG. 34  is a diagram illustrating the configuration of a communication system  3400  according to a seventh embodiment. 
     The communication system  3400  illustrated in  FIG. 34  differs from the communication system  300  illustrated in  FIG. 3  with regard to the points that routers  3412  and  3414  and a location management server  3422  are provided instead of the routers  312  and  314  and the location management server  322 , and parts other than the above points are the same as with the communication system  300 . Parts illustrated which are the same as or equivalent to those in the communication system  300  illustrated in  FIG. 3  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 34  are the same as described with reference to  FIG. 3 , so detailed description will be omitted. 
     In  FIG. 34 , the router  3412  has an interface coupled to the communication device  304  via the LAN  308 , and two interfaces coupled to the network  316 . The router  3412  includes a storage device holding the locator list  332 . The router  3412  is a relay device which relays packet communication between the communication device  304  and the network  316 , and operates based on the above-described LISP. 
     Upon receiving a MAC address resolution request from a communication device belonging to the corresponding LAN  308 , the router  3412  transmits a locator resolution request to the location management server  3422 . The transmitted locator resolution request includes, in addition to the destination IP address included in the received MAC address resolution request, the IP address of the interface of the source of the router  3412  (source locator). The router  3412  references the locator list  332  so as to acquire information of the locator corresponding to the interface of which is the source of the locator resolution request. 
     Subsequently, the router  3412  receives a locator resolution response corresponding to the locator resolution request, from the location management server  3422 . The received locator resolution response includes a MAC address resolution response transmission flag, in addition to the destination locator. A MAC address resolution response transmission flag is a flag which instructs the router which has transmitted the locator resolution request whether or not the above-described Proxy MAC address response processing will be executed. 
     In the event that the MAC address resolution response transmission flag included in the received locator resolution response instructs execution of Proxy MAC address response processing, the router  3412  performs Proxy MAC address response processing as to the source communication device of the MAC address resolution request, by a MAC address resolution response including the MAC address of its own interface. 
     The router  3414  has an interface coupled to the communication device  306  via the LAN  310 , and an interface coupled to the network  316 . The router  3414  includes a storage device holding the locator list  334 . The router  3414  is a relay device which relays packet communication between the communication device  306  and the network  316 , and operates based on the above-described LISP. 
     In the same way as with the router  3412 , in the event that the MAC address resolution response transmission flag included in the received locator resolution response instructs execution of Proxy MAC address response processing, the router  3414  performs Proxy MAC address response processing as to the source communication device of the MAC address resolution request, by a MAC address resolution response including the MAC address of its own interface. 
     The location management server  3422  receives locator resolution requests including source locators, in addition destination IP addresses, from the routers coupled to the network  316 . The location management server  3422  searches the IP address/router ID map  326 , and thereby acquires router IDs correlated with the destination IP addresses included in the received locator resolution requests (destination router IDs). Also, the location management server  3422  searches the router ID/locator map  328 , thereby acquiring router IDs correlated with source locators included in the received locator resolution requests (source router IDs). 
     The location management server  3422  then checks whether or not the acquired destination router ID and source router ID match. In the event that the acquired destination router ID and source router ID do not match, the location management server  3422  sets the MAC address resolution response transmission flag to instruct execution of the Proxy MAC address response processing. On the other hand, in the event that the acquired destination router ID and source router ID match, the location management server  3422  sets the MAC address resolution response transmission flag to not instruct execution of the Proxy MAC address response processing. 
     The location management server  3422  then transmits the response message (locator resolution response) including the MAC address resolution response transmission flag which has been set, to the source router of the locator resolution request. 
     8-2. Communication Control Method with Communication System  3400   
       FIG. 35  is a sequence chart for describing a communication control method with the communication system  3400 . Hereinafter, description will be made referencing  FIG. 34  in addition to  FIG. 35 , regarding a communication control method with the communication system  3400  in a case of transmitting packets from the interface of the communication device  304  to the interface of the communication device  306  belonging to the same logical network. 
     The communication control method illustrated in  FIG. 35  differs from the communication control method illustrated in  FIG. 7  with regard to the point that processing of steps S 3504  through S 3508  are performed instead of the processing of steps S 704  through S 708 , but processing other than these steps is the same as the communication control method illustrated in  FIG. 7 . Portions which are the same as or equivalent to those in the communication control method illustrated in  FIG. 7  are denoted with the same reference numerals. The operations and functions of the portions denoted by the same reference numerals in  FIG. 35  are the same as described with reference to  FIG. 7 , so detailed description will be omitted. 
     As illustrated in  FIG. 35 , in step S 3504 , upon having received a MAC address resolution request from the communication device  304 , the router  3412  transmits the locator resolution request to the location management server  3422 . The locator resolution request includes the destination IP address of the received MAC address resolution request, and the IP address of the interface of the source of the router  3412  (source locator). The router  3412  references the locator list  332  so as to acquire information of the locator corresponding with the interface which is the source of the locator resolution request. With the example illustrated in  FIGS. 34 and 35 , the transmitted locator resolution request includes “192.168.2.2” as the destination IP address, and includes “10.1.1.1” or “10.1.2.1” as the source locator. 
     Next, in step S 3506 , the location management server  3422  receives the locator resolution request from the router  3412 . The location management server  3422  searches the IP address/router ID map  326  based on the destination IP address included in the received locator resolution request, thereby acquiring the router ID correlated with that destination IP address (destination router ID). With the example illustrated in  FIGS. 34 and 35 , the destination IP address is “192.168.2.2”, and according to the map illustrated in  FIG. 5A  the acquired destination router ID is “R2”. 
     The location management server  3422  searches the router ID/locator map  328  based on the source locator included in the received locator resolution request, and thereby acquires the router ID correlated with that source locator (source router ID). With the example illustrated in  FIGS. 34 and 35 , the source locator is “10.1.1.1” or “10.1.2.1”, and according to the map illustrated in  FIG. 6  the acquired destination router ID is “R1”. 
     The location management server  3422  then checks whether or not the acquired destination router ID and source router ID match. In the event that the acquired destination router ID and source router ID do not match, the location management server  3422  recognizes that the interface of the communication device  306  having the destination IP address does not belong to the LAN  308  beneath the router  3412  which is the source of the locator resolution request. In the event that the acquired destination router ID and source router ID do not match, the location management server  3422  sets the MAC address resolution response transmission flag to instruct execution of the Proxy MAC address response processing. 
     On the other hand, in the event that the acquired destination router ID and source router ID match, the location management server  3422  recognizes that the interface of the communication device  306  having the destination IP address belongs to the LAN  308  beneath the router  3412  which is the source of the locator resolution request, and accordingly sets the MAC address resolution response transmission flag to not instruct execution of the Proxy MAC address response processing. 
     With the example illustrated in  FIGS. 34 and 35 , the destination router ID is “R2” and the source router ID is “R1”, so the destination router ID and source router ID do not match. Accordingly, the MAC address resolution response transmission flag is set to instruct execution of the Proxy MAC address response processing. 
     The location management server  3422  transmits a locator resolution response including the MAC address resolution response transmission flag which has been set, to the router  3412 . 
     Next, in step S 3508 , the router  3412  receives a locator resolution response from the location management server  3422 , and recognizes whether or not the MAC address resolution response transmission flag included in the received locator resolution response instructs execution of Proxy MAC address response processing. With the example illustrated in  FIGS. 34 and 35 , the router  3412  checks that the MAC address resolution response transmission flag instructs execution of the Proxy MAC address response processing, and thus recognizes that the interface of the communication device  306  having the destination IP address does not belong to the LAN  308 . 
     Next, in response to the MAC address resolution response transmission flag instructing execution of the Proxy MAC address response processing, in step S 710  the router  3412  performs Proxy MAC address response processing as to the communication device  304  which has transmitted the MAC address resolution request, by a MAC address resolution response including the MAC address of its own interface. 
     As described above, even in a case where packet communication is performed between communication devices belonging to different LANs with a communication system where one logical network is configured of multiple LANs, with the communication system  3400 , the router  3412  to which the communication device  304  which has transmitted a MAC address resolution request is coupled executes Proxy MAC address response processing as to the communication device  304  under instruction of the location management server  3422 , so packet communication may be executed in a normal manner. 
     Also, with the communication system  3400 , the location management server  3422  determines whether or not for the router  3412  to execute Proxy MAC address response processing, using maps (location information)  326  and  328  indicating the relation between IP addresses and locators, which the location management server  3422  holds. Accordingly, a database relating to location of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. Also, whether or not Proxy MAC address response processing is to be executed is centrally determined at the location management server  3422 , so the load of processing on the servers coupled to the network  316  may be alleviated. 
     8-3. Configuration of Router  3412  ( 3414 ) 
       FIG. 36  is a diagram illustrating the configuration of the router  3412  ( 3414 ) according to the seventh embodiment. 
     The router  3412  ( 3414 ) illustrated in  FIG. 36  differs from the router  312  ( 314 ) illustrated in  FIG. 8  with regard to the points that a locator resolution request generating unit  3610  and a locator resolution response processing unit  3616  are provided instead of the locator resolution request generating unit  810  and locator resolution response processing unit  816 , but is the same as the router  312  ( 314 ) other than the above points. Parts which are the same as or equivalent to those in the router  312  ( 314 ) illustrated in  FIG. 8  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 36  are the same as described with reference to  FIG. 8 , so detailed description will be omitted. 
     With the functional block illustrated in  FIG. 36 , the portions corresponding to the functions of the router  3412  ( 3414 ) relating to the Proxy MAC address response processing described with reference to  FIG. 35  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. Also, while the configuration of the router  3412  will be described, the router  3412  and  3414  have mutually equivalent configurations in the communication system  3400 . 
     The locator resolution request generating unit  3610  receives a destination IP address from the MAC address resolution request processing unit  806 . Also, the locator resolution request generating unit  3610  references the locator list  818 , thereby acquiring information of the IP address of the interface serving as the source of the locator resolution request (source locator). Based on the received destination IP address and acquired source locator, the locator resolution request generating unit  3610  generates a locator resolution request including this destination IP address and source locator. The locator resolution request generating unit  3610  outputs the generated locator resolution request to the transmission/reception unit  812 . Note that the locator list  818  is the same as the locator list  332  ( 334 ) illustrated in  FIG. 34 . 
     The locator resolution response processing unit  3616  receives a locator resolution response from the message identification unit  814 . the locator resolution response includes, in addition to the destination IP address, a MAC address resolution response transmission flag to instruct whether or not to execute Proxy MAC address response processing. 
     In the event that the MAC address resolution response transmission flag included in the received locator resolution response instructs execution of the Proxy MAC address response processing, the locator resolution response processing unit  3616  notifies the MAC address resolution response generating unit  820  to that effect, and also outputs the destination IP address included in the received locator resolution response to the MAC address resolution response generating unit  820 . 
     Note that the hardware configuration of the router  3412  ( 3414 ) is the same as the hardware configuration of the router  312  ( 314 ) illustrated in  FIG. 9 . The functions of the functional blocks of the router  3412  ( 3414 ) may be realized by the same hardware configuration as the hardware configuration of the router  312  ( 314 ) illustrated in  FIG. 9 . Accordingly, detailed description will be omitted. 
     As described above, even in a case where packet communication is performed between communication devices belonging to different LANs with a communication system where one logical network is configured of multiple LANs, the router  3412  to which the communication device  304  which has transmitted a MAC address resolution request is coupled executes Proxy MAC address response processing as to the communication device  304 , based on instruction from the location management server  3422 , so packet communication may be executed in a normal manner. 
     8-4. Configuration of Location Management Server  3422   
       FIG. 37  is a functional block diagram illustrating the configuration of the location management server  3422  according to the seventh embodiment. 
     The location management server  3422  illustrated in  FIG. 37  differs from the location management server  322  illustrated in  FIG. 10  with regard to the point that a locator resolution request processing unit  3706 , router ID searching unit  3712 , and locator resolution response generating unit  3716  are provided instead of the locator resolution request processing unit  1006 , locator searching unit  1012 , and locator resolution response generating unit  1016 , but other parts are the same. Parts which are the same as or equivalent to those in the location management server  322  illustrated in  FIG. 10  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 37  are the same as described with reference to  FIG. 10 , so detailed description will be omitted. 
     With the functional block diagram illustrated in  FIG. 37 , in the same way as with the functional block diagram illustrated in  FIG. 10  portions of the location management server  3422  which correspond to functions relating to the Proxy MAC address response processing and locator resolution processing described with reference to  FIG. 35  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. 
     The locator resolution request processing unit  3706  receives a locator resolution request from the message identification unit  1004 . The received locator resolution request includes, in addition to the destination IP address, the IP address of the interface serving as the source of the locator resolution request (source locator). 
     The locator resolution request processing unit  3706  notifies information of the destination IP address included in the received locator resolution request to the router ID searching unit  1008 . The router ID searching unit  1008  receives information of the destination IP address from the locator resolution request processing unit  3706 , and searches the IP address/router ID map  1010  based on the received destination IP address, thereby acquiring the router ID correlated with that destination IP address (destination router ID). The router ID searching unit  1008  notifies the information of the destination router ID that has been acquired to the locator resolution request processing unit  3706 . Note that the IP address/router ID map  1010  is the same as the IP address/router ID map  326  illustrated in  FIG. 34 . 
     Also, the locator resolution request processing unit  3706  notifies the information of the source locator included in the received locator resolution request to the router ID searching unit  3712 . The router ID searching unit  3712  receives the information of the source locator from the locator resolution request processing unit  3706 , and searches the router ID/locator map  1014  based on the received source locator, thereby acquiring the router IP correlated with that source locator (source router ID). The router ID searching unit  3712  notifies the information of the acquired source router ID to the locator resolution request processing unit  3706 . Note that the IP address/router ID map  1014  is the same as the IP address/router ID map  328  illustrated in  FIG. 34 . 
     The locator resolution request processing unit  3706  then checks whether or not the notified destination router ID and source router ID match. In the event that the notified destination router ID and source router ID do not match, the locator resolution request processing unit  3706  sets the MAC address resolution response transmission flag to instruct execution of the Proxy MAC address response processing. On the other hand, in the event that the destination router ID and source router ID match, the locator resolution request processing unit  3706  sets the MAC address resolution response transmission flag to not instruct execution of the Proxy MAC address response processing. 
     In addition to the destination IP address, the locator resolution request processing unit  3706  notifies the information of the MAC address resolution response transmission flag which has been set, to the locator resolution response generating unit  3716 . 
     The locator resolution response generating unit  3716  receives the information of the destination IP address and MAC address resolution response transmission flag from the locator resolution request processing unit  3706 , and generates a locator resolution response including the received destination IP address and MAC address resolution response transmission flag. The locator resolution response generating unit  3716  outputs the generated locator resolution response to the transmission/reception unit  1002 . 
     Note that the hardware configuration of the location management server  3422  is the same as the hardware configuration of the location management server  322  illustrated in  FIG. 11 . The functions of the functional blocks of the location management server  3422  may be realized with the same hardware configuration of the location management server  322  illustrated in  FIG. 11 . Accordingly, detailed description will be omitted. 
     As described above, with the communication system  3400 , the location management server  3422  operating based on LISP decides whether or not for the router  3412  to execute Proxy MAC address response processing, using the maps (location information)  326  and  328 , indicating the relation between IP addresses and locators, which the location management server  3422  itself holds. Accordingly, a database relating to location of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. Also, determination of whether or not for the location management server  3422  to execute the Proxy MAC address response processing is centrally made, so the load of processing at the servers coupled to the network  316  may be alleviated. 
     9. Eighth Embodiment 
     The following is a description of the communication system, communication control method, relay device, and information processing device according to an eighth embodiment. 
     9-1. Configuration of Communication System  3800   
       FIG. 38  is a diagram illustrating the configuration of a communication system  3800  according to an eighth embodiment,  FIGS. 39A through 39C  are diagrams illustrating examples of locator lists  332 ,  3834 , and  3844 ,  FIG. 40  is a diagram illustrating an example of an IP address/LAN ID map  3824 ,  FIG. 41  is a diagram illustrating an example of a LAN ID/router ID map  3826 , and  FIG. 42  is a diagram illustrating an example of a router ID/locator map  3828 . 
     The communication system  3800  illustrated in  FIG. 38  differs from the communication system  3400  illustrated in  FIG. 34  with regard to the points that a router  3814 , locator list  3834 , router  3842 , and locator list  3834  are provided instead of the router  3414  and the locator list  334 . The communication system  3800  differs from the communication system  3400  with regard to the points that a location management server  3822  is provided instead of the location management server  3422 , and that an IP address/LAN ID map  3824 , a LAN ID/router ID map  3826 , and a router ID/locator map  3828  are provided instead of the IP address/router ID map  326  and router ID/locator map  328 . 
     Parts of the communication system  3800  other than the above points are the same as with the communication system  300 . Parts illustrated which are the same as or equivalent to those in the communication system  300  illustrated in  FIG. 3  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 38  are the same as described with reference to  FIG. 3 , so detailed description will be omitted. 
     In  FIG. 38 , the router  3814  has an interface coupled to the communication device  304  via the LAN  308 , and two interfaces coupled to the network  316 . The router  3814  includes a storage device holding the locator list  3834 . The router  3814  is a relay device which relays packet communication between the communication device  304  and the network  316 , and operates based on the above-described LISP. 
     The locator list  3834  is a list indicating locators assigned to the router  3814 . AS illustrated in  FIG. 39B , the locator list  3834  includes two locators. That is to say, two locators (10.2.1.1 and 10.2.2.1) are assigned to the router  3814 . 
     Upon receiving a MAC address resolution request from a communication device belonging to the corresponding LAN  308 , the router  3814  transmits a locator resolution request to the location management server  3822 . The transmitted locator resolution request includes, in addition to the destination IP address included in the received MAC address resolution request, the IP address of the interface of the source of the router  3814  (source locator). The router  3814  references the locator list  3834  so as to acquire information of the locator corresponding to the interface of which is the source of the locator resolution request. 
     Subsequently, the router  3814  receives a locator resolution response corresponding to the locator resolution request from the location management server  3822 . The received locator resolution response includes a MAC address resolution response transmission flag, in addition to the destination locator. A MAC address resolution response transmission flag is a flag which instructs the router which has transmitted the locator resolution request whether or not the above-described Proxy MAC address response processing will be executed. 
     In the event that the MAC address resolution response transmission flag included in the received locator resolution response instructs execution of Proxy MAC address response processing, the router  3814  performs Proxy MAC address response processing as to the source communication device of the MAC address resolution request, by a MAC address resolution response including the MAC address of its own interface. 
     The router  3842  has an interface coupled to the communication device  306  via the LAN  310 , and an interface coupled to the network  316 . The router  3842  includes a storage device holding the locator list  3844 . The router  3842  is a relay device which relays communication between the communication device  306  and the network  316 , and operates based on the above-described LISP. 
     The locator list  3844  is a list indicating a locator assigned to the router  3842 . As illustrated in  FIG. 39C , the locator list  3844  includes one locator. That is to say, one locator (10.3.1.1) is assigned to the router  3842 . 
     In the same way as with the router  3814 , the router  3842  transmits a locator resolution request including the IP address of the source interface of the router  3842  (source locator), in addition to the destination IP address included in the received MAC address resolution request, to the location management server  3822 . 
     In the same way as with the router  3814 , in the event that the MAC address resolution response transmission flag included in the received locator resolution response instructs execution of Proxy MAC address response processing, the router  3842  performs Proxy MAC address response processing as to the source communication device of the MAC address resolution request, by a MAC address resolution response including the MAC address of its own interface. 
     The location management server  3822  Is coupled to the network  316 , and is an information processing device which operates based on the above-described LISP. The location management server  3822  includes a storage device holding the IP address/LAN ID map  3824 , a storage device holding the LAN ID/router ID map  3826 , and a storage device holding the router ID/locator map  3828 . Note that the IP address/LAN ID map  3824 , LAN ID/router ID map  3826 , and router ID/locator map  3828  may be held in a single storage device. 
     The IP address/LAN ID map  3824  is a table representing the relation between the IP addresses of the interfaces of the communication devices coupled to the network  316 , and the identification information of the corresponding LANs (LAN ID). As illustrated in  FIG. 40 , the IP address “192.168.1.1” of the interface of the communication device  304  and the LAN ID “L1” of the LAN  308  are correlated, and the IP address “192.168.2.2” of the interface of the communication device  306  and the LAN ID “L2” of the LAN  310  are correlated. That is to say, two different LANs  308  and  310  are correlated as to the interfaces of the two communication device  304  and  306  belonging to the same logical network  302 . 
     The LAN ID/router ID map  3826  is a table indicating the relation between the identification information of each LAN (LAN ID) and the identification information of the routers coupled to the LANs (router ID). As illustrated in  FIG. 41 , the LAN ID “L1” of the LAN  308  and the router ID “R1” of the router  312  are correlated, and the LAN ID “L2” of the LAN  310  and the router IDs “R2” and “R3” of the two routers  3814  and  3842  coupled to the network  316  are correlated. That is to say, with the LAN  310 , two different routers  3814  and  3842  are correlated to a single LAN. 
     The router ID/locator map  3828  is a table indicating the relation between the identification information of each router coupled to the network  316  (router ID) and corresponding locators. As illustrated in  FIG. 42 , the router ID “R1” of the router  3412  and the two locators “10.1.1.1” and “10.1.2.1” of the router  3412  are correlated, the router ID “R2” of the router  3814  and the two locators “10.2.1.1” and “10.2.2.1” of the router  3414  are correlated, and the router ID “R3” of the router  3842  and the one locator “10.3.1.1” of the router  3842  are correlated. That is to say, with the routers  3412  and  3814 , two locators are correlated to one router ID. 
     The location management server  3822  receives locator resolution requests including source locators, in addition destination IP addresses, from the routers coupled to the network  316 . The location management server  3822  searches the IP address/LAN ID map  3824 , and thereby acquires LAN IDs (destination LAN IDs) correlated to destination IP addresses included in the received locator resolution requests. 
     Also, the location management server  3822  searches the router ID/locator map  3828 , thereby acquiring router IDs correlated with source locators included in the received locator resolution requests (source router IDs). Further, the location management server  3822  searches the LAN ID/router ID map  3826 , and thereby acquires LAN IDs correlated with the acquired source router IDs (source LAN IDs). 
     The location management server  3822  then checks whether or not the acquired destination LAN ID and source LAN ID match. In the event that the acquired destination LAN ID and source LAN ID do not match, the location management server  3822  sets the MAC address resolution response transmission flag to instruct execution of the Proxy MAC address response processing. On the other hand, in the event that the acquired destination LAN ID and source LAN ID match, the location management server  3822  sets the MAC address resolution response transmission flag not to instruct execution of the Proxy MAC address response processing. 
     The location management server  3822  then transmits the response message (locator resolution response) including the MAC address resolution response transmission flag which has been set, to the source router of the locator resolution request. 
     As described above, with the communication system  3800 , two routers  3412  and  3814  are coupled to the single LAN  308 . In this case, one router does not recognize the locator information of the other router (contents of the locator list), so even in the event that the location management server  3822  transmits a locator resolution request including the information of the destination locator to the routers  3412  and  3814 , as with the case of the communication system  300  illustrated in  FIG. 3  for example, these routers  3412  and  3814  will not accurately recognize whether the interface of the communication device having the destination IP address belong to the LAN  308  beneath them, if the only information they are given is the received destination locator. 
     Accordingly, in a case where multiple routers  3414  and  3814  are coupled to the LAN  308  to which the communication device  304  which has transmitted the MAC address resolution request belongs, the location management server  3822  checks whether the destination LAN ID and source LAN ID match as described above, thereby checking whether or not the interface of the communication device having the destination IP address belongs to the LAN beneath the router which is the source of the locator resolution request. 
     Note that in the event of having received a locator resolution request having the same destination IP address from multiple different routers (in the example illustrated in  FIG. 38 , the routers  3412  and  3814 ), the location management server  3822  transmits a locator resolution response including the MAC address resolution response transmission flag set to instruct execution of the Proxy MAC address response processing, to only one of the locator resolution requests. 
     For example, the location management server  3822  transmits a locator resolution response including the MAC address resolution response transmission flag set to instruct execution of the Proxy MAC address response processing only to the locator resolution request received at the earliest timing, and for locator resolution requests having the same destination IP address received thereafter, transmits a locator resolution response including the MAC address resolution response transmission flag set to not instruct execution of the Proxy MAC address response processing. 
     9-2. Communication Control Method with Communication System  3800   
     The communication control method with the communication system  3800  differs from the communication control method of the communication system  3400  illustrated in  FIG. 35  with regard to the MAC address resolution response transmission flag setting processing executed in step S 3506  and the locator acquisition processing executed in step S 714 , but other parts are the same. 
     The MAC address resolution response transmission flag setting processing according to the communication system  3800  differs from the MAC address resolution response transmission flag setting processing according to the communication system  3400  in that the three tables of the IP address/LAN ID map  3824 , LAN ID/router ID map  3826 , and router ID/locator map  3828  are used instead of the two tables of the IP address/router ID map  326  and router ID/locator map  328 , but other parts are the same. 
     In step S 3506 , unlike the location management server  3422 , the location management server  3822  searches the IP address/LAN ID map  3824  so as to acquire a LAN ID correlated with the destination IP address included in the received locator resolution request (destination LAN ID). With the example illustrated in  FIGS. 35 and 38 , the destination IP address is “192.168.2.2”, and according to the map illustrated in  FIG. 40 , the acquired LAN ID is “L2”. 
     Further, the location management server  3822  searches the router ID/locator map  3828  so as to acquire the router ID correlated with the source locator included in the received locator resolution request (source router ID). With the example illustrated in  FIGS. 35 and 38 , the source locator is “10.0.1.1” or “10.1.2.1”, and according to the map illustrated in  FIG. 42 , the acquired router ID is “R1”. 
     Further, the location management server  3822  searches the LAN ID/router ID map  3826 , so as to acquire the LAN ID correlated with the acquired source router ID (source LAN ID). With the example illustrated in  FIGS. 35 and 38 , the source router ID is “R1”, and according to the map illustrated in  FIG. 41 , the acquired LAN ID is “L1”. 
     The location management server  3822  then checks whether to the acquired destination LAN ID and source LAN ID match. In the event that the acquired destination LAN ID and source LAN ID do not match, the location management server  3822  recognizes that the interface of the communication device  306  having the destination IP address does not belong to the LAN  308  beneath the router  3412  which is the source of the locator resolution request. In the event that the acquired destination LAN ID and source LAN ID do not match, the location management server  3822  sets the MAC address resolution response transmission flag to instruct execution of the Proxy MAC address response processing. 
     On the other hand, in the event that the acquired destination LAN ID and source LAN ID match, the location management server  3822  recognizes that the interface of the communication device  306  having the destination IP address belongs to the LAN  308  beneath the router  3412  which is the source of the locator resolution request, and sets the MAC address resolution response transmission flag to not instruct execution of the Proxy MAC address response processing. 
     With the example illustrated in  FIGS. 35 and 38 , the destination LAN ID is “L2” and the source LAN ID is “L1”, so the destination LAN ID and source LAN ID do not match. Accordingly, the MAC address resolution response transmission flag is set to instruct execution of the Proxy MAC address response processing. 
     The location management server  3822  transmits a locator resolution response including the MAC address resolution response transmission flag which has been set, to the router  3412 . 
     In step S 3508 , the router  3412  receives the locator resolution response from the location management server  3822 , and checks whether or not the MAC address resolution response transmission flag included in the received locator resolution response instructs execution of the Proxy MAC address response processing. In response to the MAC address resolution response transmission flag included in the received locator resolution response instructing execution of the Proxy MAC address response processing, in step S 710  the router  3412  performs Proxy MAC address response processing as to the communication device  304  which has transmitted the MAC address resolution request, by MAC address resolution response including the MAC address of its own interface. 
     On the other hand, the locator acquisition processing with the communication system  3800  differs from the locator acquisition processing with the communication system  3400  regarding the point that the three tables of the IP address/LAN ID map  3824 , LAN ID/router ID map  3826 , and router ID/locator map  3828  are used instead of the IP address/router ID map  326  and router ID/locator map  328 , but other points are the same. The locator acquisition processing with the communication system  3800  is the same as the locator acquisition processing with the communication system  1500 , so detailed description will be omitted. 
     As described above, even in a case where packet communication is performed between communication devices belonging to different LANs with a communication system where one logical network is configured of multiple LANs, with the communication system  3800 , the router  3412  to which the communication device  304  which has transmitted a MAC address resolution request is coupled executes Proxy MAC address response processing as to the communication device  304  based on instruction from the location management server  3822 , so packet communication may be executed in a normal manner. 
     Also, with the communication system  3800 , the location management server  3822  operating based on LISP decides whether or not for the router  3412  to execute Proxy MAC address response processing, using the maps (location information)  3824 ,  3826 , and  3828 , indicating the relation between IP addresses and locators, which the location management server  3822  itself holds. Accordingly, a database relating to location of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     Also, whether or not Proxy MAC address response processing is to be executed is centrally determined at the location management server  3822 , so the load of processing on the servers coupled to the network  316  may be alleviated. Further, even in a case where multiple routers  3412  and  3814  are coupled to the LAN  308  to which the communication device  304  which has transmitted the MAC address resolution request belongs, whether or not to execute Proxy MAC address response processing may be appropriately determined and instructed for each router. 
     9-3. Configuration of Router  3412  ( 3814 ,  3842 ) 
     The configurations of the routers  3412 ,  3814 , and  3842  in the communication system  3800  are the same as the configurations of the routers  3412  and  3414  in the communication system  3400 . Accordingly, detailed description will be omitted. 
     9-4. Configuration of Location Management Server  3822   
       FIG. 43  is a functional block diagram illustrating the configuration of the location management server  3822  according to the eighth embodiment. 
     The location management server  3822  illustrated in  FIG. 43  differs from the location management server  3422  illustrated in  FIG. 37  with regard to the points that a locator resolution request processing unit  4306  is provided instead of the location management server  3422  and locator resolution request processing unit  3706 , and that a LAN ID searching unit  4308 , an IP address/LAN ID map  4310 , a LAN ID searching unit  4312 , a LAN ID/router ID map  4314 , a router ID searching unit  4316 , and a router ID/locator map  4318  are provided instead of the router ID searching unit  1008 , IP address/router ID map  1010 , router ID searching unit  3712 , and router ID/locator map  1014 , but other parts are the same. Parts which are the same as or equivalent to those in the location management server  3422  illustrated in  FIG. 37  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 43  are the same as described with reference to  FIG. 37 , so detailed description will be omitted. 
     With the functional block diagram illustrated in  FIG. 43 , in the same way as with the functional block diagram illustrated in  FIG. 37  portions of the location management server  3822  which correspond to functions relating to the Proxy MAC address response processing and locator resolution processing described with reference to  FIG. 35  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. 
     The locator resolution request processing unit  4306  receives a locator resolution request from the message identification unit  1004 . The received locator resolution request includes, in addition to the destination IP address, the IP address of the interface serving as the source of the locator resolution request (source locator). 
     The locator resolution request processing unit  4306  notifies information of the destination IP address included in the received locator resolution request to the LAN ID searching unit  4308 . The LAN ID searching unit  4308  receives information of the destination IP address from the locator resolution request processing unit  4306 , and searches the IP address/LAN ID map  4310  based on the received destination IP address, thereby acquiring the LAN ID correlated with that destination IP address (destination LAN ID). The LAN ID searching unit  4308  notifies the information of the destination LAN ID that has been acquired to the locator resolution request processing unit  4306 . Note that the IP address/LAN ID map  4310  is the same as the IP address/LAN ID map  3824  illustrated in  FIG. 38 . 
     The locator resolution request processing unit  4306  notifies information of the source locator included in the received locator resolution request to the router ID searching unit  4316 . The router ID searching unit  4316  receives information of the source locator from the locator resolution request processing unit  4306 , and searches the router ID/locator map  4318  based on the received source locator, thereby acquiring the router ID correlated with that destination locator (destination router ID). The router ID searching unit  4316  notifies the information of the destination router ID that has been acquired to the locator resolution request processing unit  4306 . Note that the router ID/locator map  4318  is the same as the router ID/locator map  3828  illustrated in  FIG. 38 . 
     Further, the locator resolution request processing unit  4306  notifies the information of the notified source router ID to the LAN ID searching unit  4312 . The LAN ID searching unit  4312  receives the information of the source router ID from the locator resolution request processing unit  4306 , and searches the LAN ID/router ID map  4314  based on the received source router ID, thereby acquiring the LAN ID correlated with that source router ID (source LAN ID). The LAN ID searching unit  4312  notifies the information of the acquired source LAN ID to the locator resolution request processing unit  4306 . Note that the LAN ID/router ID map  4314  is the same as the LAN ID/router ID map  3826  illustrated in  FIG. 38 . 
     The locator resolution request processing unit  4306  then checks whether or not the notified destination LAN ID and source LAN ID match. In the event that the notified destination LAN ID and source LAN ID do not match, the locator resolution request processing unit  4306  sets the MAC address resolution response transmission flag to instruct execution of the Proxy MAC address response processing. On the other hand, in the event that the destination router ID and source router ID match, the locator resolution request processing unit  3706  sets the MAC address resolution response transmission flag to not instruct execution of the Proxy MAC address response processing. 
     In addition to the destination IP address, the locator resolution request processing unit  4306  notifies the information of the MAC address resolution response transmission flag which has been set, to the locator resolution response generating unit  3716 . 
     The locator resolution response generating unit  3716  receives the information of the destination IP address and MAC address resolution response transmission flag from the locator resolution request processing unit  4306 , and generates a locator resolution response including the received destination IP address and MAC address resolution response transmission flag. 
     Note that in the event of having received multiple locator resolution requests having the same destination IP address but different source locators, the locator resolution request processing unit  4306  transmits a locator resolution response including the MAC address resolution response transmission flag set to instruct execution of the Proxy MAC address response processing, to only one of the locator resolution requests. 
     For example, the locator resolution request processing unit  4306  transmits a locator resolution response including the MAC address resolution response transmission flag set to instruct execution of the Proxy MAC address response processing only to the locator resolution request received at the earliest timing, and for locator resolution requests having the same destination IP address received thereafter, transmits a locator resolution response including the MAC address resolution response transmission flag set to not instruct execution of the Proxy MAC address response processing. 
     Also, the hardware configuration of the location management server  3822  is the same as the hardware configuration of the location management server  322  illustrated in  FIG. 11 . The functions of the functional blocks of the location management server  3822  may be realized with the same hardware configuration of the location management server  322  illustrated in  FIG. 11 . The IP address/LAN ID map  4310 , LAN ID/router ID map  4314 , and router ID/locator map  4318  illustrated in  FIG. 43  are each stored in memory or a storage device. Accordingly, detailed description will be omitted. 
     As described above, with the communication system  3800 , the location management server  3822  operating based on LISP decides whether or not the router  3412  will execute Proxy MAC address response processing, using the maps (location information)  3824 ,  3826 , and  3828 , indicating the relation between IP addresses and locators, which the location management server  3822  itself holds. Accordingly, a database relating to location of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     Also, whether or not Proxy MAC address response processing is to be executed is centrally determined at the location management server  3822 , so the load of processing on the servers coupled to the network  316  may be alleviated. Further, even in a case where multiple routers  3414  and  3814  are coupled to the LAN  308  to which the communication device  304  which has transmitted the MAC address resolution request belongs, whether or not to execute Proxy MAC address response processing may be appropriately determined and instructed for each router. 
     10. Ninth Embodiment 
     The following is a description of the communication system, communication control method, relay device, and information processing device according to a ninth embodiment. 
     10-1. Configuration of Communication System  4400   
       FIG. 44  is a diagram illustrating the configuration of a communication system  4400  according to a ninth embodiment. 
     The communication system  4400  illustrated in  FIG. 44  differs from the communication system  300  illustrated in  FIG. 3  with regard to the points that routers  4412  and  4414  and a location management server  4422  are provided instead of the routers  312  and  314  and the location management server  322 , and parts other than the above points are the same as with the communication system  300 . Parts illustrated which are the same as or equivalent to those in the communication system  300  illustrated in  FIG. 3  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 44  are the same as described with reference to  FIG. 3 , so detailed description will be omitted. 
     In  FIG. 44 , the router  4412  has an interface coupled to the communication device  304  via the LAN  308 , and two interfaces coupled to the network  316 . The router  4412  includes a storage device holding the locator list  332 . The router  4412  is a relay device which relays packet communication between the communication device  304  and the network  316 , and operates based on the above-described LISP. 
     Upon receiving a MAC address resolution request from a communication device belonging to the corresponding LAN  308 , the router  4412  transmits a locator resolution request to the location management server  4422 . The transmitted locator resolution request includes, in addition to the destination IP address included in the received MAC address resolution request, the IP address of the interface of the source of the router  4412  (source locator). The router  4412  references the locator list  332  so as to acquire information of the locator corresponding to the interface of which is the source of the locator resolution request. 
     After having transmitted to the locator resolution request, the router  4412  checks whether or not a locator resolution response corresponding to the locator resolution request has been received from the location management server  4422 . The received locator resolution response includes a destination locator. 
     Upon receiving the locator resolution response from the location management server  4422 , the router  4412  performs Proxy MAC address response processing as to the source communication device of the MAC address resolution request, by a MAC address resolution response including the MAC address of its own interface. 
     The router  4414  has an interface coupled to the communication device  306  via the LAN  310 , and an interface coupled to the network  316 . The router  4414  includes a storage device holding the locator list  334 . The router  4414  is a relay device which relays packet communication between the communication device  306  and the network  316 , and operates based on the above-described LISP. 
     In the same way as with the router  4412 , upon receiving a locator resolution response from the location management server  4422 , the router  4414  performs Proxy MAC address response processing as to the source communication device of the MAC address resolution request, by MAC address resolution response including the Mac address of its own interface. 
     The location management server  4422  receives locator resolution requests including source locators, in addition destination IP addresses, from the routers coupled to the network  316 . The location management server  4422  searches the IP address/router ID map  326 , and thereby acquires router IDs correlated with the destination IP addresses included in the received locator resolution requests (destination router IDs). Also, the location management server  4422  searches the router ID/locator map  328 , thereby acquiring router IDs correlated with source locators included in the received locator resolution requests (source router IDs). 
     The location management server  4422  then checks whether or not the acquired destination router ID and source router ID match. In the event that the acquired destination router ID and source router ID do not match, the location management server  4422  transmits a locator resolution response including the destination IP address to the source router of the locator resolution request. On the other hand, in the event that the acquired destination router ID and source router ID match, the location management server  4422  does not transmit a locator resolution response. 
     10-2. Communication Control Method with Communication System  4400   
       FIG. 45  is a sequence chart for describing a communication control method with the communication system  4400 . Hereinafter, description will be made referencing  FIG. 44  in addition to  FIG. 45 , regarding a communication control method with the communication system  3800  in a case of transmitting packets from the interface of the communication device  304  to the interface of the communication device  306  belonging to the same logical network. 
     The communication control method illustrated in  FIG. 45  differs from the communication control method illustrated in  FIG. 7  with regard to the point that processing of steps S 4504  through S 4508  are performed instead of the processing of steps S 704  through S 708 , but processing other than these steps is the same as the communication control method illustrated in  FIG. 7 . Portions which are the same as or equivalent to those in the communication control method illustrated in  FIG. 7  are denoted with the same reference numerals. The operations and functions of the portions denoted by the same reference numerals in  FIG. 45  are the same as described with reference to  FIG. 7 , so detailed description will be omitted. 
     As illustrated in  FIG. 45 , in step S 4504 , upon having received a MAC address resolution request from the communication device  304 , the router  4412  transmits the locator resolution request to the location management server  4422 . The locator resolution request includes the destination IP address of the received MAC address resolution request, and the IP address of the interface of the source of the router  4412  (source locator). The router  4412  references the locator list  332  so as to acquire information of the locator corresponding with the interface which is the source of the locator resolution request. With the example illustrated in  FIGS. 44 and 45 , the transmitted locator resolution request includes “192.168.2.2” as the destination IP address, and includes “10.1.1.1” or “10.1.2.1” as the source locator. 
     Next, in step S 4506 , the location management server  4422  receives the locator resolution request from the router  4412 . The location management server  4422  searches the IP address/router ID map  326  based on the destination IP address included in the received locator resolution request, thereby acquiring the router ID correlated with that destination IP address (destination router ID). With the example illustrated in  FIGS. 44 and 45 , the destination IP address is “192.168.2.2”, and according to the map illustrated in  FIG. 5A  the acquired destination router ID is “R2”. 
     The location management server  4422  searches the router ID/locator map  328  based on the source locator included in the received locator resolution request, and thereby acquires the router ID correlated with that source locator (source router ID). With the example illustrated in  FIGS. 44  and  45 , the source locator is “10.1.1.1” or “10.1.2.1”, and according to the map illustrated in  FIG. 6  the acquired destination router ID is “R1”. 
     The location management server  4422  then checks whether or not the acquired destination router ID and source router ID match. In the event that the acquired destination router ID and source router ID do not match, the location management server  4422  transmits a locator resolution response including the destination IP address to the source router of the locator resolution request. 
     With the example illustrated in  FIGS. 44 and 45 , the destination router ID is “R2” and the source router ID is “R1”, so the destination router ID and source router ID do not match. Accordingly, the location management server  4422  transmits the locator resolution response including the destination IP address to the router  4412 . 
     Next, in step S 4508 , after having transmitted the locator resolution request to the location management server  4422  in step S 4504 , the router  4412  checks whether or not a corresponding locator resolution response has been received from the location management server  4422 . With the example illustrated in  FIGS. 44 and 45 , the router  4412  checks that the interface of the communication device  306  having the destination IP address does not belong to the LAN  308 , by receiving the locator resolution response from the location management server  4422 . 
     Next, in response to having received the locator resolution response, in step S 710  the router  4412  performs Proxy MAC address response processing as to the communication device  304  which has transmitted the MAC address resolution request, by a MAC address resolution response including the MAC address of its own interface. 
     As described above, even in a case where packet communication is performed between communication devices belonging to different LANs with a communication system where one logical network is configured of multiple LANs, with the communication system  4400  the router  4412  to which the communication device  304  which has transmitted a MAC address resolution request is coupled executes Proxy MAC address response processing as to the communication device  304  under instruction of the location management server  4422 , so packet communication may be executed in a normal manner. 
     Also, with the communication system  4400 , the location management server  4422  determines whether or not for the router  3412  to execute Proxy MAC address response processing, using maps (location information)  326  and  328  indicating the relation between IP addresses and locators, which the location management server  4422  operating based on LISP holds, and the locator resolution response is selectively transmitted to the router  4412  when instructing execution of the Proxy MAC address response processing. Accordingly, a database relating to location of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     Also, whether or not Proxy MAC address response processing is to be executed is centrally determined at the location management server  4422 , so the load of processing on the servers coupled to the network  316  may be alleviated. Also, the locator resolution response is selectively transmitted to the router  4412  when instructing execution of the Proxy MAC address response processing, so the amount of communication for transmission of the locator resolution response to the router  4412  may be reduced, and the communication load on the network  316  may be alleviated. 
     10-3. Configuration of Router  4412  ( 4414 ) 
       FIG. 46  is a diagram illustrating the configuration of the router  4412  ( 4414 ) according to the ninth embodiment. 
     The router  4412  ( 4414 ) illustrated in  FIG. 46  differs from the router  312  ( 314 ) illustrated in  FIG. 8  with regard to the points that a locator resolution request generating unit  4610  and a locator resolution response processing unit  4616  are provided instead of the locator resolution request generating unit  810  and locator resolution response processing unit  816 , but is the same as the router  312  ( 314 ) other than the above points. Parts which are the same as or equivalent to those in the router  312  ( 314 ) illustrated in  FIG. 8  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 46  are the same as described with reference to  FIG. 8 , so detailed description will be omitted. 
     With the functional block illustrated in  FIG. 46 , the portions corresponding to the functions of the router  4412  ( 4414 ) relating to the Proxy MAC address response processing described with reference to  FIG. 45  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. Also, while the configuration of the router  4412  will be described, the router  4412  and  4414  have mutually equivalent configurations in the communication system  4400 . 
     The locator resolution request generating unit  4610  receives a destination IP address from the MAC address resolution request processing unit  806 . Also, the locator resolution request generating unit  4610  references the locator list  818 , thereby acquiring information of the IP address of the interface serving as the source of the locator resolution request (source locator). Based on the received destination IP address and acquired source locator, the locator resolution request generating unit  4610  generates a locator resolution request including this destination IP address and source locator. The locator resolution request generating unit  4610  outputs the generated locator resolution request to the transmission/reception unit  812 . Note that the locator list  818  is the same as the locator list  332  ( 334 ) illustrated in  FIG. 44 . 
     After a locator resolution request generated by the locator resolution request generating unit  4610  has been transmitted from the transmission/reception unit  812 , the locator resolution response processing unit  4616  monitors whether a locator resolution response including the destination IP address has been received from the message identification unit  814 . 
     In the event of having received a locator resolution response, the locator resolution response processing unit  4616  notifies the MAC address resolution response generating unit  820  to that effect, and also outputs the destination IP address included in the received locator resolution response to the MAC address resolution response generating unit  820 . 
     Note that the hardware configuration of the router  4412  ( 4414 ) is the same as the hardware configuration of the router  312  ( 314 ) illustrated in  FIG. 9 . The functions of the functional blocks of the router  4412  ( 4414 ) may be realized by the same hardware configuration as the hardware configuration of the router  312  ( 314 ) illustrated in  FIG. 9 . Accordingly, detailed description will be omitted. 
     As described above, even in a case where packet communication is performed between communication devices belonging to different LANs with a communication system where one logical network is configured of multiple LANs, the router  4412  to which the communication device  304  which has transmitted a MAC address resolution request is coupled executes Proxy MAC address response processing as to the communication device  304  based on instruction from the location management server  4422 , so packet communication may be executed in a normal manner. 
     10-4. Configuration of Location Management server  4422   
       FIG. 47  is a functional block diagram illustrating the configuration of the location management server  4422  according to the ninth embodiment. 
     The location management server  4422  illustrated in  FIG. 47  differs from the location management server  322  illustrated in  FIG. 10  with regard to the point that a locator resolution request processing unit  4706 , router ID searching unit  4712 , and locator resolution response generating unit  4716  are provided instead of the locator resolution request processing unit  1006 , locator searching unit  1012 , and locator resolution response generating unit  1016 , but other parts are the same. Parts which are the same as or equivalent to those in the location management server  322  illustrated in  FIG. 10  are denoted with the same reference numerals. The operations and functions of the parts denoted by the same reference numerals in  FIG. 47  are the same as described with reference to  FIG. 10 , so detailed description will be omitted. 
     With the functional block diagram illustrated in  FIG. 47 , in the same way as with the functional block diagram illustrated in  FIG. 10  portions of the location management server  4422  which correspond to functions relating to the Proxy MAC address response processing and locator resolution processing described with reference to  FIG. 45  are illustrated, and description of portions corresponding to other functions is omitted from the Present Specification, since arrangements according to the related art may be used. 
     The locator resolution request processing unit  4706  receives a locator resolution request from the message identification unit  1004 . The received locator resolution request includes, in addition to the destination IP address, the IP address of the interface serving as the source of the locator resolution request (source locator). 
     The locator resolution request processing unit  4706  notifies information of the destination IP address included in the received locator resolution request to the router ID searching unit  1008 . The router ID searching unit  1008  receives information of the destination IP address from the locator resolution request processing unit  4706 , and searches the IP address/router ID map  1010  based on the received destination IP address, thereby acquiring the router ID correlated with that destination IP address (destination router ID). The router ID searching unit  1008  notifies the information of the destination router ID that has been acquired to the locator resolution request processing unit  4706 . Note that the IP address/router ID map  1010  is the same as the IP address/router ID map  326  illustrated in  FIG. 44 . 
     Also, the locator resolution request processing unit  4706  notifies the information of the source locator included in the received locator resolution request to the router ID searching unit  4712 . The router ID searching unit  4712  receives the information of the source locator from the locator resolution request processing unit  4706 , and searches the router ID/locator map  1014  based on the received source locator, thereby acquiring the router ID correlated with that source locator (source router ID). The router ID searching unit  4712  notifies the information of the acquired source router ID to the locator resolution request processing unit  4706 . Note that the router ID/locator map  1014  is the same as the router ID/locator map  328  illustrated in  FIG. 44 . 
     The locator resolution request processing unit  4706  then checks whether or not the notified destination router ID and source router ID match. In the event that the notified destination router ID and source router ID do not match, the locator resolution request processing unit  4706  decides to generate a locator resolution response, and notifies locator resolution response generating instruction information which instructs generating of a locator resolution response to the locator resolution response generating unit  4716 . The locator resolution response generating instruction information includes the destination IP address. On the other hand, in the event that the destination router ID and source router ID match, the locator resolution request processing unit  4706  decides not to generate a locator resolution response, and does not notify the locator resolution response generating instruction information to the locator resolution response generating unit  4716 . 
     Upon receiving the locator resolution response generating instruction information from the locator resolution request processing unit  4706 , the locator resolution response generating unit  4716  generates a locator resolution response including the destination IP address included in the received locator resolution response generating instruction information. The locator resolution response generating unit  4716  outputs the generated locator resolution response to the transmission/reception unit  1002 . On the other hand, the locator resolution response generating unit  4716  does not generate a locator resolution response unless locator resolution response generating instruction information is received from the locator resolution request processing unit  4706 . 
     Note that the hardware configuration of the location management server  4422  is the same as the hardware configuration of the location management server  322  illustrated in  FIG. 11 . The functions of the functional blocks of the location management server  4422  may be realized with the same hardware configuration of the location management server  322  illustrated in  FIG. 11 . Accordingly, detailed description will be omitted. 
     As described above, with the communication system  4400 , the location management server  4422  operating based on LISP decides whether or not to execute Proxy MAC address response processing, using the maps (location information)  326  and  328 , indicating the relation between IP addresses and locators, which the location management server  4422  itself holds, and the locator resolution response is selectively transmitted to the router  4412  when instructing execution of the Proxy MAC address response processing. Accordingly, a database relating to location of communication devices to perform communication does not have to be newly constructed, thereby avoiding location information of communication devices held in the overall network from becoming redundant, and enabling storage device resources such as memory to be effectively used. 
     Also, whether or not Proxy MAC address response processing is to be executed is centrally determined at the location management server  4422 , so the load of processing on the servers coupled to the network  316  may be alleviated. Also, the locator resolution response is selectively transmitted to the router  4412  when instructing execution of the Proxy MAC address response processing, so the amount of communication for transmission of the locator resolution response to the router  4412  may be reduced, and the communication load on the network  316  may be alleviated. 
     11. Other Modifications 
     (1) While an arrangement is made with the first embodiment ( FIGS. 3 through 11 ) where the location management server transmits a locator resolution response to a router including a destination locator, a locator resolution response including a destination router ID may be transmitted instead. 
     In this case, the router which has received the locator resolution response conforms whether or not the destination router ID included in the received locator resolution response and its own router ID match, and in the event that the destination router ID and the route ID of itself do not match, executes the above-described Proxy MAC address response processing. 
     (2) While an arrangement is made with the third embodiment ( FIGS. 15 through 20 ) where the location management server transmits a locator resolution response including the destination locator to the router, an arrangement may be made instead where a locator resolution response including the destination LAN ID is transmitted. 
     In this case, the router which has received the locator resolution response checks whether or not the destination LAN ID included in the received locator resolution response and the LAN ID of the LAN to which it is coupled match, and in the event that the destination LAN ID and the LAN ID of the LAN to which it is coupled do not match, executes the above-described Proxy MAC address response processing. 
     (3) While an arrangement is made with the seventh embodiment ( FIGS. 34 through 37 ) and eighth embodiment ( FIGS. 38 through 43 ) where the router transmits a locator resolution response including the destination IP address and source locator to the location management server, an arrangement may be made instead where a locator resolution response including the destination IP address and source router ID are transmitted. 
     In this case, the location management server which has received the locator resolution request acquires, based on the destination IP address included in the received locator resolution request, the destination router ID correlated with the destination IP address, and in the event that the acquired destination router ID and the source router ID included in the received locator resolution request do not match, sets a MAC address resolution response transmission flag to instruct execution of Proxy MAC address response processing. 
     Alternatively, the router may instead transmit a locator resolution request including the destination IP address and the IP address of the interface of the communication device which is the source of the MAC address resolution request (source IP address) to the location management server. 
     In this case, the location management server which has received the locator resolution request acquires, based on the destination IP address included in the received locator resolution request, the destination router ID correlated with the destination IP address, and based on the source IP address included in the received locator resolution request, acquires the router ID correlated with the source IP address. In the event that the acquired destination router ID and source router ID do not match, the location management server sets the MAC address resolution response transmission flag to instruct execution of Proxy MAC address response processing. 
     (4) While an arrangement is made with the eighth embodiment ( FIGS. 38 through 43 ) where the router transmits a locator resolution request including the destination IP address and source locator to the location management server, an arrangement may be made instead where a locator resolution request including the destination IP address and source LAN ID is transmitted. 
     In this case, the location management server which has received the locator resolution request acquires, based on the destination IP address included in the received locator resolution request, the destination LAN ID correlated with the destination IP address, and in the event that the acquired destination LAN ID and source LAN ID included in the received locator resolution request do not match, the location management server sets the MAC address resolution response transmission flag to instruct execution of Proxy MAC address response processing. 
     (5) While an arrangement is made with the eighth embodiment where the location management server transmits a locator resolution response including the MAC address resolution response transmission flag to the router, so as to make whether or not to execute Proxy MAC address response processing, and arrangement may be made instead such as with the ninth embodiment ( FIGS. 44 through 47 ) where the location management server does not transmit the locator resolution response unless instructing execution of Proxy MAC address response processing, and notifies whether or not to execute Proxy MAC address response processing by whether or not the router receives a locator resolution response after having transmitted the locator resolution request. 
     A communication system, communication control method, a relay device, and an information processing device, have been described as exemplary embodiments, but embodiments are not restricted to specifically disclosed embodiments, and various modifications and alterations may be made without departing from the Claims. 
     Also, the technology disclosed in the embodiments may be combined as suitable unless mutually contradictory. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.