JP7244106B2 - COMMUNICATION CONTROL DEVICE, COMMUNICATION CONTROL PROGRAM AND COMMUNICATION CONTROL METHOD - Google Patents

Description

The present invention relates to a communication control device, a communication control program and a communication control method, and more particularly to a communication control device, a communication control program and a communication control method under which a server accessible from a client terminal is arranged.

Routers are widely used as communication control devices that establish communication between different networks. In such communication via a router, access is made to a terminal in a network beyond the router by communication beyond the router. In such a case, it is necessary to perform domain name resolution, and Patent Document 1 discloses a technique related to this domain name resolution.

In Patent Document 1, a terminal resolves the domain name of a target server, and if a search result is not obtained, resolves the domain name of a gateway that relays to the target server. At this time, the DNS server manages the domain name of the server with a dedicated TLD (Top Level Domain) added to the end of the domain name in association with the address of the gateway. In order to resolve the domain name of the gateway, the terminal adds a dedicated TLD to the end of the domain name of the target server to resolve the domain name. The DNS server responds with the address of the gateway corresponding to the domain name with the TLD appended. When the terminal acquires the address of the gateway, it connects to the gateway according to the procedure for connecting to the gateway, and requests the gateway to connect to the target server.

JP 2010-130604 A

However, with the technique described in Patent Document 1, it is necessary to use the address of the private server on the local network (for example, local IP address) when the home client terminal within the private network accesses the private server. In other words, the setting must be changed depending on whether the client terminal is on the private network or not, which causes a problem of complicating the setting.

One aspect of the communication control apparatus according to one embodiment includes a WAN port connected to a public network in which a domain name server is arranged, and a LAN connected to a private network in which home client terminals and home server access are arranged. a port, a storage unit storing a specific subdomain name designating the home server, and a communication control unit controlling communication between the LAN port and the WAN port, wherein the communication control unit An access request relating to a specific domain name designating a home server is received from the home client terminal, a name resolution of the specific domain name is requested to the domain name server, and a second relating to the specific domain name returned from the domain name server is received. 1 matches the IP address assigned to the WAN port, the on-premises client terminal is associated with the specific subdomain name using the specific subdomain name. Also, local address acquisition processing is performed to acquire a specific internal IP address, which is the private network address of the home server.

One aspect of a communication control program according to one embodiment controls communication between a WAN port to which a public network is connected and a plurality of LAN ports to which a private network is connected, and between the plurality of LAN ports. a communication control program executed by a computing unit in a communication control device that receives an access request for a specific domain name designating a home server located on the private network from a home client terminal located on the private network. and requesting the domain name server located in the public network to resolve the specific domain name, and the external IP address indicated by the first response regarding the specific domain name returned from the domain name server is the WAN. In response to matching with the IP address assigned to the port, the specific subdomain name specifying the home server stored in the storage unit used by the computing unit is used to transfer the specific subdomain to the home client terminal. Local address acquisition processing is performed to acquire a specific internal IP address, which is the address of the private network of the home server associated with the name.

One aspect of a communication control method according to one embodiment controls communication between a WAN port to which a public network is connected and a plurality of LAN ports to which a private network is connected, and between the plurality of LAN ports. a communication control method executed by a computing unit in a communication control device, wherein an access request relating to a specific domain name designating a home server arranged in the private network is received from the home client terminal arranged in the private network. requesting a domain name server located on the public network for name resolution of the specific domain name, wherein the external IP address indicated by a first response regarding the specific domain name returned from the domain name server is the WAN port; in response to a match with the IP address assigned to the in-home client terminal, using the specific sub-domain name specifying the in-home server stored in the storage unit used by the computing unit, the in-home client terminal receives the specific sub-domain name performs a local address acquisition process for acquiring a specific internal IP address, which is the address of the private network of the home server linked to the home server.

According to the communication control device, the communication control program, and the communication control method according to the embodiment, the client terminal can access the home server regardless of the location of the client terminal without performing complicated settings on the client terminal. can let

1 is a schematic diagram of a communication system according to a first embodiment; FIG. FIG. 4 is a sequence diagram illustrating operations when a client terminal not under the control of a router accesses a private server in the communication system according to the first embodiment; FIG. 5 is a sequence diagram for explaining a problem that occurs when a client terminal under the router accesses a private server when the router according to the first embodiment is not used; 1 is a block diagram of a router according to a first embodiment; FIG. FIG. 2 is a diagram for explaining a program configuration that operates on the router according to the first embodiment; FIG. 4 is a flowchart for explaining the operation of the communication system according to the first exemplary embodiment; FIG. 4 is a sequence diagram illustrating operations when a client terminal under the router accesses a private server in the communication system according to the first embodiment; 8 is a flowchart for explaining the operation of the communication system according to the second embodiment; FIG. 11 is a sequence diagram illustrating operations when a client terminal under the router accesses a private server in the communication system according to the second embodiment;

For clarity of explanation, the following descriptions and drawings are omitted and simplified as appropriate. In addition, each element described in the drawings as a functional block that performs various processes can be configured with a CPU (Central Processing Unit), memory, and other circuits in terms of hardware, and memory implemented by a program loaded in the Therefore, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof, and are not limited to either one. In each drawing, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary.

Also, the programs described above can be stored and supplied to the computer using various types of non-transitory computer-readable media. Non-transitory computer-readable media include various types of tangible storage media. Examples of non-transitory computer-readable media include magnetic recording media (eg, flexible discs, magnetic tapes, hard disk drives), magneto-optical recording media (eg, magneto-optical discs), CD-ROMs (Read Only Memory), CD-Rs, CD-R/W, semiconductor memory (eg, mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory)). The program may also be delivered to the computer by various types of transitory computer readable media. Examples of transitory computer-readable media include electrical signals, optical signals, and electromagnetic waves. Transitory computer-readable media can deliver the program to the computer via wired channels, such as wires and optical fibers, or wireless channels.

Embodiment 1
First, the communication control device according to the first embodiment is a product called router. Therefore, the communication control device is hereinafter referred to as a router. FIG. 1 shows a block diagram of a communication system 1 according to the first embodiment. As shown in FIG. 1, in the communication system 1 according to the first embodiment, a router 10 controls communication between the private area and the public area.

In the private area, communicable terminals and servers are arranged on a private network constructed by the LAN (Local Area Network) function of the router. The example shown in FIG. 1 shows an example in which a home server (for example, private server 11) and a home client terminal (for example, client terminal 21) are arranged on a private network. In a private network, devices on the network communicate with each other using internal IP addresses issued by the router 10 . A plurality of servers and client terminals may be arranged on the private network.

The public area includes a public network provided by a telecommunications carrier or the like via a WAN (Wide Area Network) port of a router, and a communication network for communicating with client terminals and servers is constructed via the public network. FIG. 1 shows an example in which a public network 12 is connected to a router 10, and a domain name server (hereinafter referred to as a DNS server 13) and an external client terminal (for example, a client terminal 22) are arranged for the public network 12. rice field. In a public network, devices on the network communicate with each other using an external IP address issued by a predetermined organization. It is assumed that there are many servers and client terminals (not shown) placed on the public network.

Here, an IP address is defined by numbers in four fields (IPv4) or six fields (IPv6), and a combination of numbers identifies a device on the network. On the other hand, a domain name will be used in the explanation below. A domain name is a character string that identifies a server, such as abc. defghi. It is a character string that is easy for people to distinguish, such as com. Then, the domain name server has an entry that associates the domain name with the external IP address, and returns the external IP address corresponding to the inquired domain name as a response to the inquiry destination.

Further, in the communication system 1 according to the first embodiment, the first entry and the second entry are registered in the DNS server 13 when the use of the private server 11 is started. The first entry is an entry that associates a specific domain name designating a private server with a specific external IP address corresponding to the specific domain name. The second entry is an entry that associates a specific subdomain name that designates a private server with a specific internal IP address that is the private network address of the private server with the specific subdomain name. In the following description, as an example of a domain name that identifies a private server, the specific domain name will be abc. defghi. com and z.com as a specific subdomain name. abc. defghi. com.

The external IP address is an IP address managed by a server on the public network 12 and is sometimes called a global IP address. Also, the internal IP address is an IP address applicable only within the private network managed by the router 10, and is also called a local IP address. In the following description, the global IP address that designates the private server 11 is particularly referred to as a specific global IP address, and the local IP address that designates the private server 11 is specifically referred to as a specific local IP address.

The router 10 controls communication between communication devices located within the private network and between communication devices located within the private network and communication devices located on the public network 12 . Further, the router 10 controls communication between communication devices according to a predetermined protocol. In this communication control, the communication destination device is specified based on the IP address. In addition, regarding the specific domain name, when there is an access specifying the specific domain name from the client terminal 21 on the private network, the router 10 assigns the specific local IP address set in the private server 11 to the client terminal 21. Perform local address acquisition processing to be acquired. The details of this local address acquisition process will be described later.

Next, operations of the communication system 1 according to the first embodiment will be described. First, the external access operation of accessing the private server 11 on the private network managed by the router 10 from the client terminal 22 on the public network 12 in the communication system 1 according to the first embodiment will be described. In the following description, the global IP address assigned to the WAN port of the router 10 is assumed to be xxx. xxx. xxx. xxx, and the local IP address assigned to the private server 11 is yyy. yyy. yyy. Description is given as yyy.

FIG. 2 shows a sequence diagram for explaining the operation when a client terminal not under the control of a router accesses a private server in the communication system according to the first embodiment. As shown in FIG. 2 , when accessing the private server 11 from the client terminal 22 , first, the DNS server 13 is requested to resolve a specific domain name corresponding to the private server 11 . Subsequently, the DNS server 13 returns the specific global IP address associated with the specific domain name to the client terminal 22 as a response. Accordingly, the client terminal 22 recognizes the specific global IP address that designates the private server 11 . After that, the client terminal 22 accesses the router 10 using the acquired specific global IP address, and the router 10 mediates communication between the client terminal 22 and the private server 11 .

In the external access operation shown in FIG. 2, the router 10 can control the communication between the client terminal 22 and the private server 11 only by operating according to the protocol without performing any special operation.

Next, in the communication system 1 according to the first embodiment, an internal access operation to access the private server 11 from the client terminal 21 on the same private network as the private network in which the private server 11 is arranged will be described. In this internal access operation, if the local address acquisition processing according to the first embodiment is not performed, a problem arises in accessing the private server 11 using a specific domain name. In order to explain the features of the local address acquisition process according to the first embodiment in more detail, first, problems that occur when the local address acquisition process is not performed will be explained.

FIG. 3 shows a sequence diagram for explaining a problem that occurs when a client terminal under the router accesses a private server when the router according to the first embodiment is not used.

FIG. 3 is a sequence diagram for explaining the operation when the client terminal 21 under the router 10 accesses the private server 11 using a specific domain name. In this case, the client terminal 21 transmits to the router 10 an access request designating a specific domain name. The router 10 requests the DNS server 13 to resolve the specific domain name received from the client terminal 21, and the DNS server 13 returns the specific global IP address corresponding to the specific domain name to the router 10 as a response. After that, the router 10 gives the specific global IP address corresponding to the specific domain name to the client terminal 21 as a response.

However, the specific global IP address acquired by the client terminal 21 is assigned to the WAN port of the router 10, and with the specific global IP address, the client terminal 21 cannot identify the private server 11 in the same private network. can't For this reason, if the local address acquisition process according to the first embodiment is not performed, a communication error occurs in which communication devices on the same private network cannot communicate with each other using only a specific domain name.

Therefore, in the communication system 1 according to the first embodiment, the first entry and the second entry are registered in the DNS server 13 in advance. The first entry is an entry that associates a specific domain name designating the private server 11 with a specific global IP address corresponding to the specific domain name. The second entry is an entry that associates a specific subdomain name designating the private server 11 with a specific subdomain name and a specific local IP address that is the address of the private network of the private server 11 .

Then, in the communication system 1 according to the first embodiment, the router 10 is caused to perform local address acquisition processing using the first entry and the second entry. This allows the client terminal 21 to access the private server 11 only by grasping one specific domain name. Therefore, details of the router 10 according to the first embodiment will be described later.

FIG. 4 shows a block diagram of the router 10 according to the first embodiment. As shown in FIG. 4, the router 10 has a communication control section 30, a storage section 31, a wireless LAN interface 32, a wired LAN interface 33, and a WAN interface . The wireless LAN interface 32 and the wired LAN interface 33 are physical circuits that constitute LAN ports. The router 10 treats communication devices connected to the wireless LAN interface 32 or wired LAN interface 33 as devices on the private network. A WAN interface 34 is a physical circuit that constitutes a WAN port. A line connected to the public network 12 is connected to the WAN interface 34 . The router 10 uses the communication control unit 30 to control communication among the wireless LAN interface 32 , the wired LAN interface 33 and the WAN interface 34 .

The storage unit 31 also stores information used in communication control performed by the communication control unit 30 . In the example shown in FIG. 4, the storage unit 31 stores WAN-side IP information, DNS-resolved IP information, target server FQDN information, and target server CNAME information.

The WAN-side IP information is information on the global IP address set to the WAN port of the router 10 . In the router 10 according to the first embodiment, xxx. xxx. xxx. xxx is described.

The DNS-resolved IP information is global IP address information grasped by a response (hereinafter referred to as a response) to a domain name resolution inquiry (hereinafter referred to as a query) requested by the router 10 to the DNS server 13. be. In the router 10 according to the first embodiment, xxx. xxx. xxx. xxx is described.

Target server FQDN information is a specific domain name. In the router 10 according to the first embodiment, a specific domain name specifying the private server 11 is written. The target server CNAME information describes the specific subdomain name of the private server 11 described in the CNAME field, which is the specific field of the response manipulated in the local address acquisition processing described later.

In addition to many functions as a router, the communication control unit 30 performs characteristic operations when there is an access request to the private server 11 by a specific domain name specifying the private server 11 . Specifically, when the communication control unit 30 receives from the client terminal 21 an access request for a specific domain name specifying the private server 11, the communication control unit 30 requests the DNS server 13 to resolve the specific domain name. Then, when the specific global IP address indicated by the first response regarding the specific domain name returned from the DNS server 13 matches the IP address assigned to the WAN port, the communication control unit 30 selects the specific subdomain. Using the name, local address acquisition processing is performed to cause the client terminal 21 to acquire a specific local IP address associated with the specific subdomain name.

In the first embodiment, in this local address acquisition process, the communication control unit 30 operates as follows. Specifically, in the local address acquisition process according to the first embodiment, the communication control unit 30 sets the specific field in the first response, which is the name resolution result of the specific domain name returned from the DNS server 13 to the router 10. Generate a second response with the specific subdomain name in (eg, the CNAME field). The communication control unit 30 then returns this second response to the client terminal 21 .

The CNAME field, which is the specific field, is a field that specifies the transfer destination domain name of the access destination domain name. Therefore, the client terminal 21 that has received the second response refers to the specific field of the second response and requests the DNS server 13 to resolve the specific subdomain name. The private server 11 is accessed using a specific local IP address.

The communication control section 30 can be implemented by, for example, a computing section capable of executing a program. One method of realizing the communication control unit 30 is to execute the communication control program in this calculation unit to realize the above operation of the communication control unit 30 . Therefore, the program configuration that operates in the communication control unit 30 will be described. FIG. 5 shows a diagram for explaining the configuration of a program that operates on the router according to the first embodiment.

As shown in FIG. 5, programs running on the communication control unit 30 include a kernel process and a user process. The kernel process is a group of programs with a high level of safety verification and difficult to add or modify. On the other hand, the user process is a group of programs that can be easily added or modified by the user, although the safety verification level is low. In the program running on the communication control unit 30, the socket process 45 performs processing to connect the kernel process and the user process. Note that the processes shown in FIG. 5 are part of the processes executed by the communication control unit 30, and actually include many other processes.

Kernel processes include an operating system 41 , a file system 42 , a WLAN driver 43 and an Ethernet driver 44 . The operating system 41 is basic software for operating software. The file system 42 is software that defines the format of information handled by the communication control unit 30 . The WLAN driver 43 is software for operating a wireless LAN. The Ethernet driver 44 is software for operating a wired LAN.

User processes include DHCP server process 46 , port control process 47 , routing table management process 48 and DNS masquerade control process 49 . The DHCP server process 46 is software that provides a DHCP function that allocates local IP addresses to communication devices on the private network controlled by the router 10 . The port control process 47 is software that controls the protocols and information passed between the WAN and LAN ports. The routing table management process 48 is software that manages communication paths between WAN ports and LAN ports and between LAN ports. The DNS masquerade control process 49 is software that provides a domain name service to terminals in a private network not maintained by the DNS server 13 .

The router 10 realizes local address acquisition processing by causing the software shown in FIG. 5 to operate cooperatively in the communication control unit 30 . Specifically, the communication control unit 30 generates a second response in which the specific subdomain name is stored in the specific field in the first response returned from the DNS server 13 in response to the name resolution request for the specific domain name. and returns a second response to the client terminal 21 .

Next, the operation of accessing the private server 11 from the client terminal 21 under the router 10 in the communication system 1 according to the first embodiment will be described. Therefore, FIG. 6 shows a flowchart for explaining the operation of the communication system 1 according to the first embodiment.

As shown in FIG. 6, in the communication system 1 according to the first embodiment, when the client terminal 21 accesses the private server 11, the client terminal 21 generates a first DNS query regarding a specific domain name, 10 is requested to resolve a specific domain name (step S1). However, since the router 10 cannot resolve the specific domain name, this first DNS query is sent to the DNS server 13 via the router 10 (step S1).

Subsequently, the DNS server 13 refers to the first entry for the specific domain name for the received first DNS query, extracts the specific global IP address as a result of name resolution, and extracts the specific global IP address as a result of name resolution. Generate a DNS query response of 1. The DNS server 13 then returns the first query response to the router 10 (step S2). After receiving the first DNS query response, the router 10 determines whether or not the global IP address indicated by the first DNS query response matches the IP address set to the WAN port of the router 10. (step S3). In this step S3, the WAN-side IP information (the WAN port IP address stored in the setting process of the router 10) stored in the storage unit 31 by the communication control unit 30 and the IP information after DNS resolution (in the first DNS query response). Global IP address indicated).

In step S3, if the IP addresses match, the router 10 generates a second DNS query response in which the specific subdomain name is recorded in the CNAME field in the first DNS query response, and sends the second DNS query response. It is transmitted to the client terminal 21 (step S4). After that, the client terminal 21 that has received the second DNS query response refers to the CNAME field, generates a second DNS query regarding the specific subdomain name, and transmits the second DNS query to the router 10 ( step S5). Also, the router 10 that has received the second DNS query transmits the second DNS query to the DNS server 13 (step S5).

Subsequently, the DNS server 13, which has received the second DNS query, refers to the second entry regarding the specific subdomain name, extracts the specific local IP address corresponding to the specific subdomain name as a resolution result, and extracts the specific local IP address. Generate a third DNS query response that includes the address. The DNS server 13 then transmits a third DNS query response to the router 10 (step S6). This third DNS query response is sent to the client terminal 21 via the router 10 . The client terminal 21 then communicates with the private server 11 using the specific local IP address included in the third query response (step S7).

On the other hand, in step S3, if the specific global IP address indicated by the first DNS query response and the global IP address set for the WAN port of the router 10 do not match, the router 10 sends the first DNS query response. It is transmitted to the client terminal 21 (step S8). Then, the client terminal 21 accesses a private server not under the control of the router 10 using the specific global IP address indicated by the first DNS query response (step S9).

Next, the flow up to step S7 of the operations described with reference to FIG. 6 will be described using a sequence diagram. FIG. 7 shows a sequence diagram for explaining the operation when a client terminal under the router accesses a private server in the communication system according to the first embodiment. In FIG. 7, the operation of the communication system 1 will be explained using the flow of domain names or IP addresses.

As shown in FIG. 7, when a client terminal 21 under the router 10 starts accessing the private server 11 using a specific domain name, the client terminal 21 sends a first DNS query regarding the specific domain name to the router 10. to the DNS server 13 via the Subsequently, the DNS server 13 responds to the first DNS query, refers to the first entry, and returns a first DNS query response including the specific global IP address to the router 10 .

Then, if the specific global IP address indicated by the first DNS query response matches the global IP address of the WAN port of the router 10, the router 10 adds the specific subdomain name to the CNAME field of the first DNS query response. is generated and transmitted to the client terminal 21 .

The client terminal 21 then refers to the CNAME field, generates a second DNS query for the specific subdomain name, and transmits the second DNS query to the DNS server 13 via the router 10 . After that, the DNS server 13 refers to the second entry, generates a third DNS query response including the specific local IP address, and returns the third DNS query response to the client terminal 21 via the router 10. . As a result, the client terminal 21 can know the local IP address of the private server 11, and can communicate with the private server 11 using this local IP address.

As described above, the communication system 1 according to the first embodiment can perform the following operations by executing the local address acquisition processing in the router 10 . That is, in the communication system 1, even if the client terminal 21 holds only the specific domain name associated with the global IP address of the private server 11 on the same private network as the client terminal 21, the client terminal 21 and can establish communication with the private server 11 .

At this time, the operation of the router 10 is to write a specific subdomain name associated with the local IP address of the private server 11 in a specific field (for example, a CNAME field) in the first DNS query response. Different from the domain name resolution sequence. However, this modification is extremely small, and the change in operation of the router 10 is small, and the operation verification of the router 10 accompanying the addition of the local address acquisition processing is small. In addition, since the modification is small, the risk of inducing other problems is small.

Embodiment 2
Embodiment 2 describes another mode of operation of the router 10 . In the description of Embodiment 2, the same components as those in Embodiment 1 are assigned the same reference numerals as those in Embodiment 1, and descriptions thereof are omitted. Also, in the second embodiment, it should be noted that the information included in the second DNS query response is different from that in the first embodiment.

FIG. 8 shows a flowchart for explaining the operation of the communication system according to the second embodiment. As shown in FIG. 8, in the communication system according to the second embodiment, the operation after the specific global IP address indicated by the first DNS query response in step S3 matches the global IP address of the WAN port of the router 10. is different from the first embodiment. Therefore, only different operations will be described here.

As shown in FIG. 8, in the second embodiment, when the IP addresses match in step S3, the router 10 does not send a query response to the client terminal 21, and the router 10 sends a second query regarding the specific subdomain name. A DNS query is generated and sent to the DNS server 13 (step S10). Thereafter, in response to the second DNS query, the DNS server 13 refers to the second entry to extract the specific local IP address corresponding to the specific subdomain name, and makes a second DNS query containing the specific local IP address. A response is generated and a second DNS query response is returned to the router 10 (step S11).

After receiving the second DNS query response, the router 10 transmits the second DNS query response to the client terminal 21 as a response to the first DNS query (step S12). As a result, the client terminal 21 can know the specific local IP address corresponding to the private server 11, and thereafter uses the specific local IP address to communicate with the private server 11 (step S13).

As described above, in the local address acquisition process according to the second embodiment, it is possible to acquire a specific local IP address from a specific domain name corresponding to a specific global IP address only by the operation of the router 10 without depending on the client terminal 21. can.

It should be noted that the present invention is not limited to the above embodiments, and can be modified as appropriate without departing from the scope of the invention.

1 Communication System 10 Router 11 Private Server 12 Public Network 13 DNS Server 21 Client Terminal 22 Client Terminal 30 Communication Control Section 31 Storage Section 32 Wireless LAN Interface 33 Wired LAN Interface 34 WAN Interface 41 Operation System 42 File System 43 WLAN Driver 44 Ethernet Driver 45 Socket 46 DHCP Server Process 47 Port Control Process 48 Routing Table Management Process 49 DNS Masquerade Control Process

Claims (7)

a WAN port connected to a public network where domain name servers are located;
a LAN port connected to a private network where the home client terminal and the home server access are arranged;
a storage unit that stores a specific subdomain name that designates the home server;
a communication control unit that controls communication between the LAN port and the WAN port;
The communication control unit
receiving an access request for a specific domain name designating the in-house server from the in-house client terminal;
requesting the domain name server to resolve the specific domain name;
using the specific subdomain name in response to an external IP address indicated by a first response for the specific domain name returned from the domain name server matching the IP address assigned to the WAN port; A communication control device for performing local address acquisition processing for causing the home client terminal to acquire a specific internal IP address linked to the specific subdomain name. The communication control unit, in the local address acquisition process,
generating a second response that stores the specific subdomain name in a specific field in the first response;
returning the second response to the in-home client terminal;
The in-home client terminal
By referring to the specific field of the second response, using the specific internal IP address included in the third response obtained by requesting the domain name server to resolve the specific subdomain name, 2. The communication control device according to claim 1, which accesses a server. 3. The communication control device according to claim 2, wherein said specific field is a field for designating a transfer destination domain name of an access destination domain name. The communication control unit, in the local address acquisition process,
requesting the domain name server to resolve the specific subdomain name in response to receiving the first response;
receiving a name resolution result of the specific subdomain name as a second response from the domain name server;
2. The communication control apparatus according to claim 1, wherein said specific internal IP address included in said second response is given to said home client terminal as a name resolution result of said specific domain name. The domain name server has a first entry that associates a specific domain name designating the home server with a specific external IP address corresponding to the specific domain name, a specific subdomain name designating the home server, and the 5. The communication control according to any one of claims 1 to 4, wherein a second entry that associates a specific subdomain name with a specific internal IP address that is an address of the private network of the home server is registered in advance. Device. A communication control program executed by a computing unit in a communication control device for controlling communication between a WAN port to which a public network is connected and a LAN port to which a private network is connected, and between the LAN ports,
receiving an access request for a specific domain name designating a home server located on the private network from a home client terminal located on the private network;
Requesting name resolution of the specific domain name from a domain name server located on the public network;
In response to the fact that the external IP address indicated by the first response regarding the specific domain name returned from the domain name server matches the IP address assigned to the WAN port, A communication control program for performing local address acquisition processing for causing the in-house client terminal to acquire a specific internal IP address linked to the specific subdomain name using the stored specific subdomain name specifying the in-house server. A communication control method executed by an arithmetic unit in a communication control device for controlling communication between a WAN port connected to a public network and a LAN port connected to a private network and between the LAN ports,
receiving an access request for a specific domain name designating a home server located on the private network from a home client terminal located on the private network;
Requesting name resolution of the specific domain name from a domain name server located on the public network;
In response to the fact that the external IP address indicated by the first response regarding the specific domain name returned from the domain name server matches the IP address assigned to the WAN port, A communication control method for performing a local address acquisition process for causing the in-house client terminal to acquire a specific internal IP address linked to the specific sub-domain name using the stored specific sub-domain name specifying the in-house server.

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