JP4514780B2 - Communication apparatus and communication method - Google Patents

Description

  The present invention relates to a name resolution method when a plurality of networks are connected.

  Conventionally, in an IP (Internet Protocol) network, a node in the network is uniquely specified by an IP address. This IP address is a numeric string and is difficult for humans to remember. Therefore, a DNS (Domain Name System) that associates character string information called a domain name (hereinafter also referred to as FQDN (Fully Qualified Domain Name)) with an IP address is generally used so that it can be easily identified by humans. In a DNS network, when application software (hereinafter referred to as an application) of a client device specifies a FQDN and accesses a server, a process for converting the FQDN into an IP address is required. In this way, converting an FQDN to an IP address corresponding to the FQDN is called name resolution. Here, a function unit that generates and transmits a name resolution request packet in response to an application request is called a DNS resolver, and a DNS server that is a server program that generates and responds to a name resolution result packet corresponding to the received name resolution request packet. An apparatus provided with a program is called a DNS server.

  In general, name resolution is performed as follows. That is, the application of the client device notifies the DNS resolver of the FQDN input from the input device. The DNS resolver generates a name resolution request packet including the input FQDN and transmits it to the DNS server (name resolution server). The DNS server that has received the name resolution request packet stores in advance name resolution information that is information that associates the FQDN with the IP address, and names the IP address corresponding to the FQDN included in the received name resolution request packet. A name resolution result packet including the detected IP address is generated and transmitted from the resolution information. The Internet is provided with such DNS servers in a distributed manner, and the DNS server constitutes a tree structure with the DNS root server as a vertex. That is, even if the DNS resolver performs name resolution of the FQDN that cannot be resolved to the nearby DNS server, the DNS resolver can finally acquire the IP address corresponding to the FQDN.

  However, in recent years, the forms of networks connected to client devices have diversified, and the general name resolution method as described above cannot always uniquely identify a DNS server that performs appropriate name resolution. ing. For example, recent networks include special networks such as networks provided by telecommunications carriers and Internet providers, closed networks formed for each region, private networks formed for each company, and local area networks (LANs). Network. Furthermore, in these special networks, name resolution is possible with a so-called DNS server on the Internet, but communication is not possible or restricted for a host having an IP address associated with the domain name. There is also a network.

  Furthermore, recent networks include a network that performs communication based on the conventional Internet protocol IPv4 (Internet Protocol Version 4) and a network that performs communication based on IPv6 (Internet Protocol Version 6), which has been widely used as the next generation Internet protocol. And a network that performs packet transfer by both IPv4 and IPv6.

  As described above, for example, a method in which a client device connected to various networks performs name resolution may be a method in which a name resolution request packet is transmitted at a time to DNS servers included in all connected networks. . The DNS resolver uses an IP address based on a name resolution result that has a higher priority according to a predetermined priority, for example, among the name resolution results that have responded to such a name resolution request. Here, the predetermined priority order is, for example, adopting the name resolution result received earliest after the transmission of the name resolution request packet, or a priority order set in advance according to the reliability of each domain.

  As another method for client devices connected to various networks to make a name resolution request in this way, name resolution for sequentially inquiring DNS servers included in all connected networks in a predetermined order. A method for transmitting a request packet is conceivable.

  Furthermore, in such name resolution, it is desirable to shorten the time from the transmission of the name resolution request packet to the response as much as possible. Therefore, a method of temporarily saving (cache) the name resolution result can be considered. For example, a client device having a DNS resolver that performs a name resolution request or a relay device that relays a name resolution request packet stores name resolution result information (information about FQDN and corresponding IP address) obtained once, or For the FQDN that performs name resolution with high frequency, a name resolution request is issued when the client device or the relay device is activated, and the name resolution result is stored. When a name resolution request for the same stored FQDN is made or received, the name resolution request is not transmitted to the DNS server, but the stored name resolution result is used (for example, Patent Document 1, Non-Patent Document 1) Patent Document 1).

In this way, if the name resolution result is temporarily stored (cached) by a DNS resolver or a name resolution relay device, the number of name resolution requests to the DNS server on the network is reduced, and the name resolution result is obtained. Time can be shortened. Generally, in such a cache, the name resolution result (IP address) that has passed the expiration date is invalidated according to the expiration date set for each name resolution result.
JP 2004-297494 A "DNS & BIND (4th edition)", Paul Albitz (original), Cricket Liu (author), Hiroaki Takada (translation). Ikuo Kojima (translation), Mitsumasa Kodate (translation) Published by O'Reilly Japan February 26, 2002

However, the conventional techniques related to the method for performing name resolution in various network forms as described above have the following problems.
First, in the method of transmitting a name resolution request packet to the DNS servers of all connected networks at a time, the DNS resolution request packet is transmitted to all the DNS servers to which the DNS resolver is connected. Therefore, an excessive processing load is imposed on a higher-level server such as a root server, which is not a desirable method.

  In addition, in the case of a domain on a special network, name resolution cannot be performed by a DNS server on the Internet. Therefore, when name resolution request packets are sent to a plurality of DNS servers on the Internet at one time, name resolution cannot be performed. A plurality of resolution requests reach the root server. This places a burden on the DNS on the network and the Internet, and is not a desirable method because it does not satisfy the recommended rules for using the Internet according to the so-called RFC (Request for Comments) recommendation.

  In the method of sequentially sending name resolution requests to the DNS servers of the connected network, it may take a long time to finally reach the DNS server that performs name resolution. Furthermore, when the DNS server that has received the name resolution request does not store the name resolution result corresponding to the request, the DNS server does not always respond with information indicating that name resolution cannot be performed. That is, the DNS server may not respond to the name resolution request. The DNS resolver that has transmitted the name resolution request is in a waiting state until a preset waiting time elapses (timeout). As described above, when sequentially executing inquiries, a long time may elapse until a response is obtained. Here, if a time exceeding the timeout limit of the DNS resolver elapses, the user cannot receive a service for connecting to the network. That is, name resolution by sequential inquiry is not a desirable method in consideration of the convenience of the user of the client device.

  Further, in a mixed environment of IPv4 network and IPv6 network, a name resolution method that solves the following three problems is desirable. First, the headers of IPv4 packets and IPv6 packets in the network layer (layer 3) are not compatible. Second, in layer 4 and above, a single A (A) query that inquires an address in IPv4 format, a quad A (AAA) query that inquires an address in IPv6 format, and an address that inquires addresses in either IPv4 format or IPv6 format. There is a query format. Thirdly, in various network forms as described above, the scope of FQDNs that can be resolved by each DNS server is different. It is necessary to have a mechanism to determine the correct name resolution by making an inquiry to the DNS server on which network for various name resolution requests transmitted in a state where these three issues are arbitrarily combined. .

In addition, client devices connected to diversified networks in recent years are PCs (Personal Computers) and PDAs (Personal Digital Assistants), and there are variations in functions and performance. It is not always appropriate to perform complicated processing for the above.
The present invention has been made in view of such a situation, and provides a communication apparatus and method having a DNS proxy function for efficiently performing name resolution in a state connected to various network forms as described above. .

  In order to solve the above-described problem, the present invention is a communication apparatus capable of IP communication that performs name resolution by any DNS server provided in a network, and is capable of name resolution of domain name information and domain name information. Corresponding to the domain name information included in the input first name resolution request information, and storage means (for example, the storage unit 230-1) for preliminarily associating and storing connection auxiliary information for accessing the DNS server Name resolution control means for determining whether or not the connection auxiliary information is stored in the storage means (for example, name resolution control unit 260-1), the name resolution control means is connected to the storage means corresponding to the domain name information If it is determined that the information is stored, the connection information is read, and based on the read connection auxiliary information, the domain name information is sent to a DNS server capable of name resolution. Name resolution proxy means (for example, name resolution proxy unit 250) that transmits second name resolution request information including domain name information and receives name resolution result information corresponding to the second name resolution request information from the DNS server. -1).

  In the present invention, the storage means described above includes first correspondence information (for example, Phase 1) that is information in which domain name information is associated with a DNS server IP address that is an IP address of a DNS server that can resolve the domain name information. The table 232-1) is stored in advance as connection auxiliary information, and the name resolution proxy means stores the DNS server IP address corresponding to the domain name information as first correspondence information in the storage means. If the DNS server IP address is the destination, the first name resolution request information is transmitted as the second name resolution request information, and the name resolution corresponding to the second name resolution request information is transmitted. Name resolution including first name resolution proxy means (for example, Phase 1 processing unit 252-1) that receives the result information and outputs the name resolution result information And further comprising a result output means.

  In the present invention, the above-described network performs communication using the first network protocol and the second network protocol, and the first name resolution request information is name resolution request information based on the first network protocol. The DNS server performs name resolution by the second network protocol, and the storage means corresponds to the domain name information, the IP address of the first network predetermined by the first network protocol, and the domain name information. Second correspondence information (for example, Phase 0 table 231-1), which is information associated with an IP address of the second network that is an IP address according to the second network protocol, is stored as connection auxiliary information, and name resolution is performed. The control means has a first network address corresponding to the domain name information. Name resolution result output means for outputting the IP address of the first network as the name resolution result (for example, name resolution result transmission unit 280- 1) is further provided.

  In the present invention, the name resolution proxy means described above transmits second name resolution request information including domain name information to the DNS server by the second network protocol, and corresponds to the second name resolution request information. It includes a second name resolution proxy means (for example, Phase 0 processing unit 251-1) that receives the second name resolution result information, and the name resolution control means is a second network corresponding to the IP address of the first network. When the IP address is determined not to be stored as the second correspondence information in the storage means, the second name resolution proxy means is operated.

  The present invention detects the IP address of the second network corresponding to the second domain name information from the second name resolution result information received by the second name resolution proxy means described above, and detects the detected second The information processing apparatus further includes correspondence information updating means (for example, correspondence information updating unit 240-1) that stores information in which the IP address of the network and domain name information are associated with each other as second correspondence information.

  When the present invention receives an IP packet whose destination is the IP address of the first network according to the first network protocol described above, the IP address of the first network is obtained from the second correspondence information stored in the storage means. Protocol conversion means (for example, IP header) that reads the IP address of the second network corresponding to the IP address and converts the header information of the IP packet into header information based on the second network protocol destined for the IP address of the second network It further includes a conversion unit 220-1).

  In the present invention, the above-mentioned storage means has a third correspondence in which a predetermined priority order, a DNS server IP address, and status information indicating whether communication to the DNS server IP address is valid or invalid are associated with each other. The information is stored, and the name resolution proxy means detects from the storage means the DNS server IP address indicating that the status information is valid and has the highest priority among the third correspondence information. Third name resolution proxy means for transferring the first name resolution request information as second name resolution request information to the DNS server IP address and receiving name resolution result information corresponding to the second name resolution request information (For example, Phase 2 processing unit 253-1), the name resolution control unit includes a first stored in the storage unit, information corresponding to the domain name information included in the first name resolution request information. Not detectable or from the corresponding information, or not detectable or the second correspondence information stored in the storage means, or in the case of both, characterized in that to operate the third name resolution proxy means.

  In the present invention, the above-mentioned name resolution proxy means either makes a name resolution request for a DNS server IP address stored in advance, or makes a name resolution request for a DNS server IP address received from a DHCP server. And a fourth name resolution proxy means (for example, Phase 3 processing unit 254-1) for performing name resolution. The name resolution control means includes a third name resolution proxy means stored in the storage means. In the case where the DNS server IP address is not detected from the correspondence information, the fourth name resolution proxy means is operated.

  The present invention is a communication method of a communication apparatus capable of IP communication that performs name resolution by any of the DNS servers provided in the above-described network, and the domain name information and the domain name information can be resolved in the storage means. A step of preliminarily storing the connection auxiliary information for accessing the DNS server in association with each other, and the name resolution control means includes connection auxiliary information corresponding to the domain name information included in the input first name resolution request information. The step of determining whether or not the information is stored in the storage means and the name resolution control means determine that the connection information corresponding to the domain name information included in the first name resolution request information is stored in the storage means In this case, the DNS server capable of name resolution proxy means for reading the connection information and resolving the domain name information based on the read connection auxiliary information Transmits a second name resolution request information including the domain name information, characterized by comprising the steps of: receiving a name resolution result information corresponding from the DNS server to the second name resolution request information.

  In the present invention, the storage means described above includes the first correspondence information that is information in which the domain name information is associated with the DNS server IP address that is the IP address of the DNS server that can resolve the domain name information. When the name resolution control means determines that the DNS server IP address corresponding to the domain name information is stored as the first correspondence information in the storage means, the name resolution proxy means includes the first The name resolution proxy means sends the first name resolution request information as the second name resolution request information with the DNS server IP address as the destination, and the name resolution result information corresponding to the second name resolution request information And a name resolution result output means that outputs name resolution result information.

  In the present invention, the above-described network performs communication using the first network protocol and the second network protocol, and the first name resolution request information is name resolution request information based on the first network protocol. The DNS server performs name resolution by the second network protocol, and stores the domain name information, the IP address of the first network predetermined by the first network protocol, and the domain name information in the storage means. A step of storing second correspondence information, which is information associated with an IP address of a second network, which is an IP address according to the second network protocol, as connection auxiliary information; The control means has a first network address corresponding to the domain name information If it is determined to be stored as the second correspondence information 憶 means, characterized in that it comprises a step of outputting the IP address of the first network as a name resolution result.

  In the present invention, the second name resolution proxy means included in the name resolution proxy means transmits second name resolution request information including domain name information to the DNS server by the second network protocol. Receiving the second name resolution result information corresponding to the name resolution request information of the second name, and the name resolution control means, the IP address of the second network corresponding to the IP address of the first network is stored in the storage means A step of operating the second name resolution proxy means when it is determined that the second correspondence information is not stored.

  According to the present invention, the correspondence information update unit detects the IP address of the second network corresponding to the second domain name information from the second name resolution result information received by the second name resolution proxy unit. The storage unit stores information associating the detected IP address of the second network with the domain name information as the second correspondence information.

  In the present invention, when the above protocol conversion means receives an IP packet destined for the IP address of the first network according to the first network protocol, the first correspondence information stored in the storage means is used as the first correspondence information. Reading out the IP address of the second network corresponding to the IP address of the second network, and converting the header information of the IP packet into header information according to the second network protocol destined for the IP address of the second network. It is characterized by that.

  In the present invention, the above-mentioned storage means has a third correspondence in which a predetermined priority order, a DNS server IP address, and status information indicating whether communication to the DNS server IP address is valid or invalid are associated with each other. The third name resolution proxy means that stores the information and the name resolution proxy means includes that the status information is valid among the third correspondence information from the storage means and has the highest priority. The DNS server IP address indicated is detected, the first name resolution request information is transferred to the detected DNS server IP address as second name resolution request information, and the name corresponding to the second name resolution request information The step of receiving the resolution result information, and the name resolution control means detects the information corresponding to the domain name information included in the first name resolution request information from the first correspondence information stored in the storage means. Or it can not be, or not detectable or the second correspondence information stored in the storage means, or in the case of both, characterized in that it comprises the steps of: operating a third name resolution proxy means.

  In the present invention, the fourth name resolution proxy means included in the above-described name resolution proxy means makes a name resolution request to a DNS server IP address stored in advance, or for a DNS server IP address received from a DHCP server The name resolution request by means of performing a name resolution request, and the name resolution control means, the third name resolution proxy means from the third correspondence information stored in the storage means, the DNS server IP The fourth name resolution proxy means is operated when no address is detected.

  As described above, according to the present invention, when a name resolution request including a domain name stored in advance is input in an environment connected to various networks, a connection related to a predetermined optimum DNS server is established. Since the auxiliary information is detected and the name resolution request is represented, it is efficiently identified whether the name resolution request can be obtained for which DNS server of the plurality of networks. Communication means can be provided.

  Further, according to the present invention, when a name resolution request including a domain name stored in advance is input, the IP address of the DNS server corresponding to the domain name is stored in advance, and based on the stored IP address Since the transmission of the name resolution request is used as a proxy, the name resolution request can be made only to the DNS server determined to be optimal in advance without transmitting the name resolution request to all of the connectable DNS servers.

  Further, according to the present invention, the second correspondence information that is information in which the first network address according to the first network protocol is associated with the second network address according to the second network protocol is stored in advance. Since the first network address is output in response to the name resolution request, the network protocol based on the name resolution request information and the network protocol of the DNS server that can resolve the name resolution result are also different. The name resolution result corresponding to the input name resolution request can be output.

  Further, according to the present invention, when the name resolution request information according to the first network protocol is received, and the IP address according to the second network protocol corresponding to the domain name included in the name resolution request information is not stored In addition, since the name resolution request to the DNS server capable of resolving the name resolution request is made on behalf, the name resolution result in the latest network environment can be output.

  Further, according to the present invention, the name resolution result by the second network protocol is stored, and when the name resolution request including the already stored domain name is received, the name resolution request is not performed again. The corresponding name resolution result can be output.

  Further, according to the present invention, the header information of the IP packet destined for the first network address according to the first network protocol is used as the destination and the second network address stored in advance corresponding to the first network address as the destination. Therefore, communication between devices using different network protocols can be made possible.

  Furthermore, according to the present invention, when it is detected that the name cannot be resolved by the above-described method, a name resolution request is transmitted to a communicable DNS server selected based on a predetermined priority order. Therefore, even when there are routes to a plurality of communicable DNS servers, name resolution can be performed based on the priority order. As described above, since the name resolution request is made to the DNS server with the highest priority among the communicable paths, the load on the network and the DNS server can be minimized.

  Further, according to the present invention, when it is detected that the name cannot be resolved by the above-described method, a DNS server IP address is transmitted to the DNS server IP address stored in advance or received from the DHCP server. Since the name resolution is performed by either of the name resolution requests to the network, it is possible to connect to any DNS server on the network. According to this, the situation where name resolution cannot be performed and the situation where communication with the partner indicated by the FQDN is impossible can be avoided as much as possible.

  As described above, according to the present invention, by using a plurality of name resolution request means, a name resolution result for a name resolution request to various types of networks can be provided without burdening the network as much as possible. It is possible to provide a function as a DNS proxy that virtually shows a single DNS server to a DNS resolver that sends a resolution request.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
<Network environment>
FIG. 1 is a diagram illustrating a network environment using a communication device according to an embodiment of the present invention. The network environment according to the present embodiment includes an IPv4 closed network 900, an IPv4 client device 100-2 and an IPv6 client device 101-1 that can communicate with the IPv4 closed network 900, an IPv4 client device 100-2, and an IPv4 closed network 900. Line terminating device 200-2 for relaying communication, line terminating device 200-3 for relaying communication between IPv6 client apparatus 101-1 and IPv4 closed network 900, DNS server 911 provided in IPv4 closed network 900, IPv4 The IPv4 Internet 301 connected to the closed network 900, the IPv4 DNS server 311 and the information server 521 provided in the IPv4 Internet 301, and the IPv4 closed network 900 are connected. IPv4 private network 501, the IPv4 private network 501 IPv4 comprises a private DNS server 511 and the information server 520 and the information server 524 is provided.

  Furthermore, the network environment according to the present embodiment includes an IPv6 closed network 901, an IPv4 client device 100-1 and an IPv6 client device 101-2 that can communicate with the IPv6 closed network 901, an IPv4 client device 100-1 and an IPv6 closed network. A line termination device 200-1 that relays communication with the network 901, a line termination device 200-4 that relays communication between the IPv6 client device 101-2 and the IPv6 closed network 901, and a DNS server 912 provided in the IPv6 closed network 901. IPv6 Internet 302 connected to IPv6 closed network 901, IPv6 DNS server 312 and information server 523 included in IPv6 Internet 302, IPv6 closed network 901 With the connected IPv6 private network 502, IPv6 private network 502 comprises IPv6 and private DNS server 512 and the information server 520 is provided. Here, the IPv4 Internet 301 and the IPv6 Internet 302 include a route server 10 and a DNS server 11.

The root server 10 stores information at the apex of the DNS server tree structure. The DNS server 11 is a DNS server that performs name resolution using both IPv4 and IPv6 network protocols.
The IPv4 closed network 900 is a network that performs IPv4 communication. The line termination device 200-2 is a communication device that relays communication between the IPv4 closed network 900 and the IPv4 client device 100-2 used by the user. The IPv4 client device 100-2 is a communication terminal used by a user, and is, for example, a PC or a PDA. The IPv4 client apparatus 100-2 performs network communication using IPv4.

  The line termination device 200-3 has the same configuration as the line termination device 200-2. The line termination device 200-3 is a communication device that relays communication between the IPv4 closed network 900 and the IPv6 client device 101-1 used by the user. The IPv6 client device 101-1 is a communication terminal used by a user. The IPv6 client apparatus 101-1 performs network communication using IPv6.

  The DNS server 911 is a server that performs name resolution of the FQDN used in the IPv4 closed network. When connected to the route server 10, the DNS server 911 can resolve the name of the global domain and is used only in the IPv4 closed network 900. A server that can also perform name resolution of a special domain, and is provided in the IPv4 closed network 900. The IPv4 Internet 301 is a network provided by an ISP (Internet Service Provider), for example, and is connected to the Internet. The information server 521 is a server device that provides a service by information communication via a network, and is, for example, a web server. The IPv4 DNS server 311 performs name resolution of the domain name by IPv4.

  Here, the terms related to the domain used in the following description are defined. First, the global domain is a network area or subnet that can be connected to the Internet, and is a so-called WAN (Wide Area Network). A global domain name is a unique character string registered on an organization that manages combinations of domain names and global IP addresses, such as IANA (Internet Assigned Numbers Authority), which is guaranteed on the Internet. It is.

  Such a domain name is usually a host (server) indicated by a domain name represented by an alphanumeric character string, and is converted into a global IP address by a DNS server that can communicate with a DNS root server on the Internet. Is possible. Here, the DNS root server is a server that stores information on the apex (TLD, Top Level Domain) of the domain name space in the DNS. That is, each DNS server provided in the global domain performs a recursive search and obtains an IP address when the domain name received by the name resolution request is not stored in the device itself and there is no cache data. Search for. In the recursive search, an inquiry is made by tracing to the DNS root server to obtain the IP address of the DNS server corresponding to the TLD of the domain name to be searched. Thereafter, the DNS server of the lower domain is sequentially traced and a name resolution request is made. A DNS server that stores an IP address corresponding to the received domain name is searched for and an IP address is acquired.

  However, even if it is possible to perform such name resolution, whether the host is actually on the Internet (whether it has packet reachability) and whether it can be resolved. It becomes an independent event. That is, as shown in FIG. 2, the name can be resolved by the route server 10 on the Internet, but communication with the host 1001 having the IP address as the name resolution result may be limited. For example, the host 1001 shown in FIG. 2 is a host having a domain name “aaa.com” and an IP address “99.88.77.66”, and is an ISP-B network operated by ISP-B. A host provided in a private network 1004, which is a closed network provided in 1003. Here, the ISP-B network 1003 is configured to relay, for example, communication from only a communication device approved in advance to the host 1001.

  The route server 10 stores the IP address “99.88.77.66” as name resolution information in association with “aaa.com”, for example. Here, the communication device 1005 sends a name resolution request for the domain name “aaa.com” from the route server 10 either via the ISP-A network 1002 or the ISP-B network 1003. It is possible to receive the name resolution result including the information of the IP address “99.88.77.66” as a response to. However, when connecting to the IP address “99.88.77.66”, the communication device 1005 must pass through the ISP-B network 1003, and the connection is restricted by the ISP-B network 1003. For example, connection to the host 1001 provided in the private network 1004 is not possible. For example, in FIG. 1, such special domain names are assigned to the information server 520 and the information server 522.

  Next, the local domain is a network area or subnet that is not connected to the Internet, and is a so-called LAN (Local Area Network). The local domain name is a character string given to the host or area by the user, and is not guaranteed unique. Such a domain name cannot be converted into an IP address by a DNS route server. A local domain name can usually be resolved only by a DNS server installed by a user or a LAN builder. Also in this case, whether or not name resolution is possible and whether or not there is packet reachability to the host indicated by the name resolution result are independent events. In FIG. 1, for example, the information server 520 is a local domain. Here, a local domain and a domain of a host that can be resolved by a DNS server provided in the global domain, such as the host 1001 shown in FIG. The domain name in the special domain is called a special domain name.

  The IPv4 private network 501 in FIG. 1 is a special domain. That is, the IPv4 private network 501 is a closed network connected to the IPv4 closed network 900, and access restrictions are imposed by the administrator of the IPv4 private network 501. The IPv4 private network 501 includes an IPv4 private DNS server 511. For example, the IPv4 private DNS server 511 performs name resolution of a domain name associated with a host provided in the IPv4 private network 501. The domain name that is resolved in the IPv4 private network 501 is a special domain name.

  The IPv6 closed network 901 is an IP network that performs communication using IPv6. The line termination device 200-1 has the same configuration as the line termination device 200-2, and is a communication device that relays communication between the IPv6 closed network 901 and the IPv4 client device 100-1 used by the user. The IPv4 client device 100-1 is a communication terminal used by a user. The IPv4 client device 100-1 performs network communication using IPv4.

  The line termination device 200-4 has the same configuration as the line termination device 200-3. The line terminating device 200-4 is a communication device that relays communication between the IPv6 closed network 901 and the IPv6 client device 101-2 used by the user. The IPv6 client apparatus 101-2 is a communication terminal used by the user. The IPv6 client device 101-2 performs network communication using IPv6.

  The DNS server 912 is a server that performs name resolution of the FQDN used in the IPv6 closed network. When connected to the route server 10, the DNS server 912 can resolve the name of the global domain and is used only in the IPv6 closed network 901. A server that can also perform name resolution of a special domain, and is provided in the IPv6 closed network 901. The IPv6 Internet 302 is a network provided by an ISP (Internet Service Provider), for example, and is connected to the Internet. The IPv6 DNS server 312 performs name resolution of the domain name. The information server 523 is a server device that provides a service by information communication via a network, and is, for example, a web server.

  The IPv6 private network 502 is a special domain. That is, the IPv6 private network 502 is a closed network connected to the IPv6 closed network 901, and access restrictions are imposed by the administrator of the IPv6 private network 502. The IPv6 private DNS server 512 performs name resolution of a special domain name associated with a host provided in the IPv6 private network 502, for example. The information server 522 is a server device that provides a service based on information communication via a network, and is, for example, a web server.

As described above, the line termination devices of the line termination device 200-1, the line termination device 200-2, the line termination device 200-3, and the line termination device 200-4 have the same configuration. It is a communication apparatus which enables communication between hosts of various network forms as shown.
Although FIG. 1 shows the IPv4 closed network 900 and the IPv6 closed network 901 as networks connected to the Internet, there may be a plurality of each network. Further, there may be a plurality of private networks connected to the IPv4 closed network 900 and the IPv6 closed network 901, and a plurality of line termination devices and client devices may exist.

<Communication device: Configuration>
FIG. 3 is a block diagram showing a configuration of the line terminating device 200-1 which is a communication device according to the present embodiment.
The line termination device 200-1 is, for example, a network relay device provided by a telecommunications carrier or a network service provider, and provides a connection environment to the network to a client device used by a user. The line termination device 200-1 includes a communication unit 210-1, an IP header conversion unit 220-1, a storage unit 230-1, a correspondence information update unit 240-1, a DHCP client unit 245-1, and a DHCP server. Unit 246-1, name resolution proxy unit 250-1, name resolution control unit 260-1, name resolution request reception unit 270-1, name resolution result transmission unit 280-1, DNS resolver 290-1 It has.

  The communication unit 210-1 communicates with an external network such as the Internet. The external network includes, for example, a network that performs packet transfer by IPv4, a network that performs packet transfer by IPv6, and a network that performs packet transfer by both IPv4 and IPv6. In the present embodiment, the network includes a global domain and a special domain as described above.

  The communication unit 210-1 includes, for example, an IPv4 communication unit 211-1 and an IPv6 communication unit 212-1. The IPv4 communication unit 211-1 performs communication using an IPv4 packet, and the IPv6 communication unit 212-1 performs communication using an IPv6 packet. The IP packet is roughly divided into a header part and a body part, and the header part is different between the IPv4 packet and the IPv6 packet. That is, IPv4 header information is added to the IPv4 packet, and IPv6 header information is added to the IPv6 packet. Here, the body part may be arbitrary data. Currently, two types of IPv4 and IPv6 are generally used.

  The IP header conversion unit 220-1 performs mutual conversion between the header part of the IPv4 packet and the header part of the IPv6 packet. The IP header conversion unit 220-1 converts the protocol of the IP packet by converting the header part.

The storage unit 230-1 is a storage unit that stores information necessary for relaying communication between the client device 100-1 and an external network. The storage unit 230-1 includes a Phase 0 table 231-1, a Phase 1 table 232-1, and a logical IF. And a storage unit 233-1.
The Phase 0 table 231-1 is a storage unit for information necessary for the phase 0 processing unit 251-1 to be described later to perform name resolution. An example of the data structure stored in the Phase 0 table 231-1 is shown in FIG. The Phase 0 table 231-1, for example, associates the virtual address that is unique in the Phase 0 table 231-1 with the character string information indicating the domain name of the information server that can be accessed only by IPv6, and the IP address of the information server. The real address shown is stored.

  Hereinafter, a set of information of a domain name, a virtual address associated with the domain name, and a real address stored in the Phase 0 table 231-1 is referred to as a Phase 0 record. In this embodiment, the virtual address is a predetermined IPv4 address, and the real address is an address of an information server that can be accessed only by IPv6. In this embodiment, the virtual address and the real address are addresses based on different protocols, but addresses based on the same protocol may be stored. The virtual address may be a predetermined IPv6 address, and the real address may be an information server address accessible only by IPv4.

  The Phase 1 table 232-1 is a storage unit that stores information for the Phase 1 processing unit 252-1 to detect a name resolution destination. An example of the data structure of the Phase1 table 232-1 is shown in FIG. The Phase 1 table 232-1 stores a primary DNS server address and a secondary DNS server address capable of resolving the domain name in association with the domain name. Hereinafter, a set of information of the primary DNS server address and the secondary DNS server address stored in the Phase 1 table 232-1 in association with the domain name is referred to as a Phase 1 record.

  The domain name stored in the Phase 1 table 232-1 is normally FQDN, and a special domain name is stored in the present embodiment. The stored domain name may not be a special domain name, and a global domain name may be stored. The primary DNS server address is a so-called primary DNS server in DNS. In other words, it is recommended that DNS be operated by two DNS servers, a primary DNS server and a secondary DNS server, for troubleshooting and load balancing. Here, the primary DNS server is a DNS server of the main system.

  The secondary DNS server is a DNS server of a secondary system that plays a role of backup for dealing with a failure or distributing a load of an inquiry. The secondary DNS server periodically copies forward and reverse information from the primary DNS server and stores the data. The administrator and user of the line terminating device 200-1 store appropriate values in the Phase1 table 232-1 in advance. Note that the address of each DNS server stored in the Phase 1 table 232-1 may be based on IPv4 or IPv6. In this embodiment, it is assumed that the address is based on IPv4.

  Here, in the present embodiment, the IP address of a DNS server capable of name resolution of the special domain and its subdomain is set in the Phase 1 table 232-1. The IP address of the DNS server may be either IPv4 or IPv6. It is also possible to designate a plurality of DNS servers such as a primary DNS server and a secondary DNS server.

  The logical IF storage unit 233-1 is a storage unit that stores information for the Phase 2 processing unit 253-1 to perform name resolution processing. An example of the data structure of the logical IF storage unit 233-1 is shown in FIG. The logical IF storage unit 233 stores, for example, a priority, a logical IF state, and a DNS server address in association with logical IF identification information that is identification information of a logical IF (interface).

  The logical IF identification information is information for identifying a logical IF connected to the network, and is, for example, character string information. The priority is information indicating a predetermined priority, for example, numerical information. In the present embodiment, the lower the numerical value, the higher the priority. The logical IF storage unit 233-1 stores connection information to a DNS server capable of global domain name resolution. For example, when connected to a plurality of ISPs, each of the plurality of ISPs provides the information. Among the DNS servers, information for determining which DNS server to send the name resolution request is the priority. In the logical IF state, the logical IF control unit 242-1 stores whether the connection state of each logical IF is valid, for example, “active” or “inactive”. The DNS server address indicates the IP address of the DNS server on the network ahead of each logical IF. Hereinafter, a set of information including priority, logical IF status, and DNS server address stored in the logical IF storage unit 233-1 in association with the logical IF identification information is referred to as a logical IF record. .

The correspondence information update unit 240-1 stores the IPv6 address received by the Phase0 processing unit 251 in the Phase0 table 231-1 in association with the corresponding domain name and a predetermined virtual IPv4 address.
The controlled unit 241-1 communicates with a control device that manages the line termination device 200-1, and the device state such as the physical state, communication state, and past operation (log) of the line termination device 200-1. Is transmitted to the name resolution control unit 260-1, for example, and is transmitted to the control device that manages the own terminal via the network. Also, the setting information as described above is received from the control device that manages the terminal, and is reflected in each setting value of the terminal.

  The DHCP client unit 245-1 communicates with a DHCP (Dynamic Host Configuration Protocol) server via the communication unit 210-1, and acquires the IP address of the default DNS server. The DHCP client unit 245-1 operates in a Phase 3 process described later. The DHCP server unit 246-1 transmits network information in response to a DHCP information request transmitted from a subordinate client terminal.

In accordance with the name resolution request packet received by the name resolution request receiving unit 270-1, the name resolution proxy unit 250-1 accesses the appropriate DNS server to perform name resolution, and outputs a name resolution result packet. The name resolution proxy unit 250-1 includes four types of name resolution processing units: a phase 0 processing unit 251-1, a phase 1 processing unit 252-1, a phase 2 processing unit 253-1, and a phase 3 processing unit 254-1. According to the request content of the name resolution request packet received by the resolution request receiving unit 270-1, the name resolution control unit 260-1 selects and processes an optimum name resolution proxy unit among these name resolution proxy units. To perform efficient name resolution.
When the name resolution request receiving unit 270-1 receives the name resolution request packet, the name resolution control unit 260-1 determines which of the Phase 0 processing unit 251-1 to Phase 3 processing unit 254-1 is the processing subject for name resolution. And the processing unit determined to be the processing subject is operated.

The name resolution request receiving unit 270-1 receives the name resolution request packet via the communication unit 210-1. The name resolution result transmission unit 280-1 transmits the name resolution result output from the name resolution proxy unit 250-1 to the client device via the communication unit 210-1.
The DNS resolver 290-1 is a part that operates as client software in the name resolution process in the line termination device 200-1. The DNS resolver 290-1 transmits a name resolution request to the name resolution control unit 260-1 when a name resolution request is required in the line termination device 200-1. Here, in the name resolution request packet that is an IP packet, when an IPv4 address is requested, an A query (so-called single A) is designated in the body portion. On the other hand, when an IPv6 address is requested, an AAAA query (so-called quad A) is designated in the body part. Further, when an address of either IPv4 or IPv6 or both is requested, an any query is designated.

That is, in a situation where IPv4 and IPv6 network environments coexist, name resolution request packets based on combinations of the following six patterns of protocols and queries are transmitted. First, an AAAA query based on IPv6. The second is an A query based on IPv6. The third is an AAAA query by IPv4. The fourth is an A query based on IPv4. Fifth, any query by IPv6. Sixth, it is an any query by IPv4. The line terminating device 200-1 according to the present embodiment can respond to these six types of name resolution request packets.
The DNS resolver 290-1 includes an IPv4 DNS resolver 291-1 and an IPv6 DNS resolver 292-1. The IPv4 DNS resolver 291-1 makes a name resolution request for the A query, AAAA query, and any query by IPv4. The IPv6 DNS resolver 292-1 makes a name resolution request for the A query, AAAA query, and any query by IPv6.

  7 to 9 are block diagrams showing the internal configuration of each of the line terminator 200-2 to the line terminator 200-4 for the explanation of the following embodiment. FIG. 7 is a diagram illustrating the line termination device 200-2. FIG. 8 is a diagram illustrating the line termination device 200-3. FIG. 9 is a diagram illustrating the line termination device 200-4. Each functional block with the same name included in the line terminating device 200-1, the line terminating device 200-3, and the line terminating device 200-4 has the same configuration as that of the line terminating device 200-1.

  FIG. 10 is a block diagram illustrating a configuration of an IPv4 client device 100-1 that is a terminal device used by a user. The IPv4 client apparatus 100-1 is, for example, a computer terminal such as a PC or a PDA, and includes an input unit such as a keyboard and buttons, a screen that is an output unit, and the like.

  The IPv4 client device 100-1 includes, for example, an application 110-1, an IPv4 DNS resolver 120-1, and an IPv4 communication unit 130-1. The application 110-1 is application software for connecting to a network, such as an Internet browser or mail software, and performs name resolution by the IPv4 DNS resolver 120-1. The IPv4 DNS resolver 120-1 is a name resolution target domain name that is a target for performing a name resolution request in response to a network connection request of an application 110, an OS (Operating System), or other software that operates on the IPv4 client apparatus 100-1. Is generated and transmitted to the DNS server via the IPv4 communication unit 130-1, and a name resolution result packet as a response to the name resolution request is received. The IPv4 communication unit 130-1 performs communication control using IPv4. That is, the IPv4 communication unit 130-1 generates an IP packet based on the IPv4 packet and communicates with the connected communication device.

  FIG. 11 is a diagram illustrating a configuration of the IPv4 client apparatus 100-2. Each functional block with the same name included in the IPv4 client apparatus 100-2 has the same configuration as each functional block included in the IPv4 client apparatus 100-1.

  FIG. 12 is a block diagram illustrating a configuration of an IPv6 client device 101-1 that is a terminal device used by a user. The IPv6 client apparatus 101-1 is, for example, a computer terminal such as a PC or PDA, and includes an input unit such as a keyboard and buttons, a screen that is an output unit, and the like.

  The IPv6 client apparatus 101-1 includes, for example, an application 111-1, an IPv6 DNS resolver 121-1, and an IPv6 communication unit 131-1. The application 111-1 is application software that performs network connection, such as an Internet browser or mail software. In response to the network connection request from the application 111-1, the IPv6 DNS resolver 121-1 generates a name resolution request packet including a name resolution target domain name that is a target of the name resolution request, and sets the IPv6 communication unit 131-1. The name resolution result packet is received as a response to the name resolution request. The IPv6 communication unit 131-1 performs communication control using IPv6. In other words, the IPv6 communication unit 131-1 generates an IPv6 IP packet and communicates with the connected communication device.

  FIG. 13 is a diagram illustrating a configuration of the IPv6 client apparatus 101-2. Each functional block with the same name included in the IPv6 client apparatus 101-2 has the same configuration as each functional block included in the IPv6 client apparatus 101-1.

<First embodiment: Phase 0: IP conversion>
Hereinafter, an embodiment in which the above-described communication device relays communication among various forms of client devices, DNS servers, and information servers will be described.
In the following description, an IP packet (M) (M = IPv4 or IPv6) indicates an IP packet whose network layer (layer 3) protocol is M. For example, an IP packet (IPv4) indicates an IP packet based on IPv4.

  In the following description, a name resolution request packet (M, N) (M = IPv4 or IPv6, N = A or AAAA) indicates a name resolution packet including an N query in the body portion. For example, “name resolution request packet (IPv4, A)” indicates an A query by IPv4. In addition, when a name resolution target domain name that is a domain name for which an IP address is to be obtained is indicated, it is expressed as a name resolution request packet (M, N, name resolution target domain name). For example, “name resolution request packet (IPv4, A, domain name of information server 521)” indicates an A query by IPv4 with the name resolution target domain name as the domain name of information server 521.

  In the following description, the name resolution result packet according to the protocol M, which stores the IP address corresponding to the domain name that is the name resolution request target, is referred to as the name resolution result packet (M, name resolution). Request domain name, name resolution result IP address). For example, a name resolution result packet (IPv4, domain name of information server 523, IPv4 virtual address) is a response to a name resolution request in which the domain name of information server 523 is a name resolution target domain name, and an IPv4 virtual address is The name resolution result packet by IPv4 stored as a name resolution result IP address is shown.

FIG. 14 and FIG. 15 are diagrams showing tables in which the network form in which the communication apparatus according to the present embodiment relays communication is classified into 10 patterns (type A to type J).
In the first embodiment, an operation example in which the name resolution processing in the network corresponding to the type G shown in FIG. 15 is performed by the Phase 0 processing unit 251-1 will be described. In the first embodiment, the IPv4 client device 100-1 that performs communication using IPv4 transmits an IP packet to the information server 523 that performs communication using IPv6. Here, the line terminating device 200-1 relays information communication from the IPv4 client device 100-1 to the information server 523. The name resolution of the domain name of the information server 523 is performed by the IPv6 DNS server 312.

FIG. 16 is a sequence diagram illustrating an operation example in which the line terminating device 200-1 according to the present embodiment relays communication from the IPv4 client device 100-1. Hereinafter, with reference to FIG. 16, an operation example of communication processing in the present embodiment will be described.
First, the user inputs the domain name of the information server 523 as destination information via the input unit provided in the IPv4 client apparatus 100-1. The application 110-1 transmits the input domain name of the information server 523 to the IPv4 DNS resolver 120-1. Then, the IPv4 DNS resolver 120-1 generates a name resolution request packet (IPv4, A, domain name of the information server 523) and transmits it to the line terminating device 200-1 (step S1000).

When the name resolution request receiving unit 270-1 of the line terminating device 200-1 receives the name resolution request packet via the IPv4 communication unit 211-1, the name resolution control unit 260-1 first receives the name resolution request packet. A Phase 0 determination process for determining whether or not the name resolution processing of the name resolution request packet is performed by the Phase 0 processing unit 251-1 is performed. Here, after the IPv4 client device 100-1 transmits the name resolution request packet in step S1000, step S1001, step S1002, step S1003, and step S1004 in which the line termination device 200-1 acts as a proxy for the name resolution process. This process will be described in detail with reference to FIG.
FIG. 17 is a flowchart showing Phase 0 determination processing and Phase 0 processing that is name resolution processing by Phase 0.

  The name resolution control unit 260-1 reads the query stored in the body part of the name resolution request packet received by the name resolution request reception unit 270-1, and determines whether or not it is a single A (step S101). . When the name resolution control unit 260-1 determines that the query read from the name resolution request packet is not single A (step S101—NO), the name resolution control unit 260-1 determines whether the query is quad A (step S151).

  On the other hand, when the name resolution control unit 260-1 determines that the received name resolution request packet is single A (step S101-YES), the name resolution control reception unit 270-1 The name resolution target domain name (domain name of the information server 523) is read from the received name resolution request packet, and whether information matching the read name resolution target domain name exists in the domain name item of the Phase 0 table 231-1. It is determined whether or not (step S102, step S103).

  If the name resolution control unit 260-1 determines that the resolution request domain name is not stored in the Phase 0 table 231-1, the name resolution control unit 260-1 excludes the resolution request domain name from the Phase 0 process. And proceed to Phase 1 (step S103—NO).

  On the other hand, if the name resolution control unit 260-1 determines that the domain name that matches the name resolution target domain name (domain name of the information server 523) is stored in the Phase 0 table 231-1 (YES in step S103). The Phase 0 processing unit 251-1 reads the Phase 0 record of the virtual address and the real address corresponding to the domain name that matches the name resolution target domain name (domain name of the information server 523) from the Phase 0 table 231-1 ( Step S111).

  Then, the Phase 0 processing unit 251-1 stores the name resolution result packet (IPv4, IPv4, which stores the virtual address included in the Phase 0 record detected in Step S 111 as the name resolution result IP address via the name resolution result transmission unit 280-1. The domain name and virtual address of the information server 523 are generated and transmitted to the IPv4 client apparatus 100-1 as a response to the name resolution request packet (IPv4, A, domain name of the information server 523) (step S112, FIG. 16). Step S1001).

  When the Phase 0 processing unit 251-1 determines that the real address (IPv6) is not included in the Phase 0 record detected in Step S 111 (Step S 113 -NO), the IPv6 DNS resolver 292 determines the name resolution target domain name (information Name resolution request packet (IPv6, AAAA, domain name of information server 523) storing the domain name of server 523) is generated, and IPv6 DNS resolver 292 recursively transmits it to name resolution control unit 260-1 (step S114). .

  When the name resolution control unit 260-1 recursively receives a name resolution request packet (IPv6, AAAA, domain name of the information server 523), the name resolution control unit 260-1 determines that the Phase 0 process is not performed in the Phase 0 determination process. As a result, processing is performed in any one of Phase 1 to Phase 3 described later. A name resolution request packet is transmitted according to the determination result of the name resolution control unit 260-1 (step S1003 in FIG. 16), and a name resolution result packet (IPv6, domain name of information server 523, IP address of information server 523) is received. (Step S1004 in FIG. 16).

  The correspondence information update unit 240 reads the name resolution result IP address (IP address of the information server 523) from the received name resolution result packet, and selects a domain name that matches the name resolution target domain name (domain name of the information server 523). It is updated so as to be associated with the included Phase 0 record, and stored in the Phase 0 table 231 (step S115).

  When the name resolution request packet received by the name resolution request receiving unit 270-1 is quad A, the processing from step S151 to step S165 is the same as the processing from step S101 to step S115 described above. Since the difference is only that IPv4 and IPv6 are opposite, the description is omitted. For example, when the client terminal is a terminal that can communicate only with IPv6 and the name resolution request packet transmitted by the client terminal cannot be single A, the determination process of step S101 is not performed. May be.

  Next, in step S112, the IPv4 client apparatus 100-1 transmits an IP packet to the information server 523 according to the virtual address included in the name resolution result packet that the line termination apparatus 200-1 responds to the IPv4 client apparatus 100-1. An example of operation in which the line terminating device 200-1 relays will be described with reference to FIG.

  The IPv4 communication unit 130-1 of the IPv4 client apparatus 100-1 transmits an IP packet (IPv4) using the virtual address included in the name resolution result packet received in step S1001 as the destination address. The IPv4 communication unit 211-1 of the line terminating device 200-1 receives the IP packet (IPv4) transmitted from the IPv4 client device 100-1 (step S1002). As described above, the name resolution control unit 260-1 makes a name resolution request to the IPv6 DNS server 312 (step S1003), and receives the name resolution result (step S1004). Then, the IP header conversion unit 220 reads the destination address included in the header portion of the IP packet (IPv4) received in step S1002.

  The IP header converting unit 220-1 determines whether or not the same address as the read destination address is stored in the virtual address item of the Phase 0 table 231-1. When the IP header conversion unit 220 detects the same information as the destination address from the virtual address item of the Phase 0 table 231-1, the IP header conversion unit 220 reads the Phase 0 record corresponding to the virtual address. The IP header conversion unit 220-1 replaces the header part of the IP packet (IPv6) received in step S1001 with an IPv6 header part whose destination address is the real address included in the read Phase 0 record (IPv6). Generate (step S1005).

Then, the IP header conversion unit 220-1 transmits the generated IP packet (IPv6) to the information server 523 via the IPv6 communication unit 212-1 (step S1006).
The information server 523 generates a response IP packet (IPv6) as a response to the IP packet (IPv6) transmitted from the line terminating device 200-1, and transmits it to the line terminating device 200-1 (step S1007).

  Then, when the IPv6 communication unit 212-1 of the line terminating device 200-1 receives the response IP packet (IPv6) transmitted from the information server 523, the IP header conversion unit 220-1 receives the response IP packet (IPv6). A response IP packet (IPv4) is generated by replacing the header part with the IPv4 header part (step S1008). Then, the IP header conversion unit 220 transmits a response IP packet to the IPv4 client device 100-1 via the IPv4 communication unit 211 (step S1009).

  Note that the line terminating device 200-1 receives a name resolution request packet from the IPv4 client device 100-1 in step S1000 described above, and then makes a name resolution request to the IPv6 DNS server 312. Here, the name resolution fails. In step S1001, the process after step S1001 may not be performed as a name resolution error. FIG. 18 shows a sequence when the line terminating device 200-1 operates in this way. In FIG. 18, the operations from step S1000, step S1001, and steps S1002 to S1009 are the same as the operations shown in FIG. 16, but in FIG. A name resolution request is made to the IPv6 DNS server 312 (step S1000-1), and a response from the IPv6 DNS server 312 is received (step S1000-2).

  As described above, after the IPv4 client device 100-1 transmits the name resolution request packet in step S1000, the line termination device 200-1 performs steps S1000-1 for proxying the name resolution processing and steps S1000-2. The process will be described in detail with reference to FIG. FIG. 19 is a flowchart showing Phase 0 determination processing and Phase 0 processing that is name resolution processing by Phase 0. The processing from step S101 to step S111 is the same as the processing described above with reference to FIG.

  When the Phase 0 processing unit 251-1 determines that the actual address (IPv6) is not included in the Phase 0 record detected in Step S111 (Step S131-NO), the IPv6 DNS resolver 292 determines the name resolution target domain name (information server 523). The name resolution request packet (IPv6, AAAA, domain name of the information server 523) is generated, and the IPv6 DNS resolver 292 recursively transmits it to the name resolution control unit 260-1 (step S132).

  When the name resolution control unit 260-1 recursively receives a name resolution request packet (IPv6, AAAA, domain name of the information server 523), the name resolution control unit 260-1 determines that the Phase 0 process is not performed in the Phase 0 determination process. As a result, processing is performed in any one of Phase 1 to Phase 3 described later. A name resolution request packet is transmitted according to the determination result of the name resolution control unit 260-1, and a name resolution result packet (IPv6, domain name of the information server 523, IP address of the information server 523) is received. If name resolution fails here (step S133-NO), the processing after step S134 is not performed as a name resolution error.

  The correspondence information update unit 240 reads the name resolution result IP address (IP address of the information server 523) from the received name resolution result packet, and selects a domain name that matches the name resolution target domain name (domain name of the information server 523). It is updated so as to be associated with the included Phase 0 record, and stored in the Phase 0 table 231 (step S134).

  The Phase 0 processing unit 251-1 stores a name resolution result packet (IPv4, information server) that stores, as the name resolution result IP address, the virtual address included in the Phase 0 record detected in Step S 111 via the name resolution result transmission unit 280-1. 523 domain name, virtual address) is generated and transmitted to the IPv4 client apparatus 100-1 as a response to the name resolution request packet (IPv4, A, domain name of the information server 523) (step S135).

  When the name resolution request packet received by the name resolution request receiving unit 270-1 is quad A, the processing from step S181 to step S185 is the same as the processing from step S131 to step S135 described above, and IPv4. Is the only difference between IPv6 and IPv6, and the description thereof is omitted.

  As described above, according to the name resolution by the Phase 0 processing unit 251-1, it is possible to perform name resolution between a client device that can communicate only with IPv4 and a host (server) that can communicate only with IPv6. Similarly, it is possible to perform name resolution between a client device that can communicate only with IPv6 and a host (server) that can communicate only with IPv4. That is, when a client device acquires an IP address corresponding to a domain name for which name resolution is to be performed, the client device cannot recognize a DNS server capable of name resolution or a network protocol (IPv4 or IPv6) supported by an access destination host. Even in this case, name resolution can be performed.

  Further, the Phase 0 record of the Phase 0 table 231 updated and stored by the Phase 0 processing unit 251-1 becomes invalid when the valid time (TTL (time to live)) included in the name resolution result has passed. As described above, when the valid time of the name resolution result expires, the name resolution result becomes invalid. Therefore, even when the DNS server performs load distribution by the round robin method, the effect of the distribution by the round robin method is effective. It can be. Here, generally, the valid time of the name resolution result of the DNS server performing round robin is set short.

  Although IPv6 is the next generation version of IPv4, it is not compatible in terms of interconnection. That is, a client that can perform IPv4 communication but cannot perform IPv6 communication cannot communicate with a host to which information is provided only by IPv6. Here, it cannot be said that the IPv6 support of network-related devices has been completed, and a coexistence technique of IPv4 and IPv6 is required. Several methods have been proposed for mutual conversion of IP packets of IPv4 and IPv6, but it cannot be said that means linked with the DNS mechanism has been established.

  For example, when an IPv4 client device that can communicate only with IPv4 and an IPv6 server that can communicate only with IPv6 communicate, the IPv4 client device and the IPv6 server cannot directly communicate with each other. is required. Therefore, for example, it is conceivable to use a NAT (Network Address Translation) function as the address translation means. Therefore, in order to communicate using NAT, an IPv4 and IPv6 address correspondence table is required in advance.

  Therefore, according to the Phase 0 process applying the name resolution mechanism as described above, an address correspondence table between IPv4 and IPv6 can be dynamically generated. In addition, a mechanism for transmitting a virtual address (a virtual address may be IPv4 or IPv6) stored in the Phase 0 table 231-1 that is an address correspondence table between IPv4 and IPv6 to the client apparatus is also Phase 0. It can be provided by the processing unit 251-1.

Also, if the contents of the single A query and quad A (AAAA) query of the name resolution request packet received from the client device are changed, the client device cannot communicate even if the name resolution result can be obtained. . According to the Phase 0 process, a transparent operation can be performed without changing the query.
As described above, according to the Phase 0 process, even if the communication protocol between the client device and the information server is different, communication can be established by linking the address translation function unit and the name resolution mechanism.

  According to the first embodiment described above, for example, an information server (for example, the information server 523) provided by the client apparatus (for example, the IPv4 client apparatus 100-1) that supports only IPv4 only with IPv6. ) To have a protocol conversion function (convert IPv4 and IPv6) on the communication path between the IPv4 client apparatus 100-1 and the information server 523 (for example, the line termination apparatus 200- 1), if the line terminating device 200-1 returns a virtual IPv4 server address, a client device that supports only IPv4 can receive a service from an information server that supports only IPv6. Is possible.

  In step S102, when the name resolution control unit 250-1 determines whether or not the Phase 0 record corresponding to the name resolution target domain name exists in the Phase 0 table 231-1, the name resolution target domain name. Only the Phase 0 record that completely matches the name may be determined, or the name resolution target domain name that is the subdomain name of the Phase 0 record may be determined. In this case, for example, when the name resolution target domain name is “bbb.aaa.com”, if there is a Phase 0 record storing “aaa.com” in the DNS server address item, the name resolution target domain name is set. It is determined that the corresponding Phase 0 record exists.

<Second Embodiment: Phase 1: Special Domain>
In the second embodiment, an operation example in which the name resolution processing in the network corresponding to the type A illustrated in FIG. 14 is performed by the Phase 1 processing unit 252-2 will be described. In the second embodiment, an IPv4 client apparatus 100-2 that performs communication using IPv4 transmits an IP packet using the information server 520 that can be connected only via the IPv4 private network 501 as a destination address. Here, the line terminating device 200-2 relays information communication from the IPv4 client device 100-2 to the information server 520. The name resolution of the domain name of the information server 520 is performed by the IPv4 private DNS server 511.

FIG. 20 is a sequence diagram illustrating an operation example in which the line termination device 200-2 according to the present embodiment relays communication from the IPv4 client device 100-2. Hereinafter, with reference to FIG. 20, an operation example of the communication processing in the present embodiment will be described.
First, the user inputs the domain name of the information server 520 as destination information via the input unit provided in the IPv4 client apparatus 100-2. The application 110-2 transmits the input domain name of the information server 520 to the IPv4 DNS resolver 120-2. Then, the IPv4 DNS resolver 120-2 generates a name resolution request packet (IPv4, A, domain name of the information server 520) and transmits it to the line terminating device 200-2 (step S1010).

  When the name resolution request receiving unit 270-2 of the line termination device 200-2 receives the name resolution request packet (IPv4, A, domain name of the information server 520) via the IPv4 communication unit 211-2, the name First, the resolution control unit 260-2 performs Phase 0 determination processing for determining whether or not the name resolution processing of the received name resolution request packet is performed by the Phase 0 processing unit 251-2.

  If the name resolution control unit 260-2 determines not to perform name resolution in Phase 0 in the Phase 0 determination process of Step S100 described above (Step S100-NO), the name resolution control unit 260-2 determines the Phase 1 processing unit. In Step 252-2, a Phase 1 determination process is performed to determine whether to perform a name resolution process. Here, the processing in steps S1011 and S1012 in which the line terminating device 200-2 acts as a proxy for name resolution will be described in detail with reference to FIG.

  FIG. 21 is a flowchart showing Phase 1 determination processing and Phase 1 processing that is name resolution processing by Phase 1. The name resolution control unit 260-2 determines that the domain name that matches the name resolution target domain name (domain name of the information server 520) included in the name resolution request packet is the domain name of the Phase1 table 232-2 of the storage unit 230-2. It is determined whether it is stored in the item (step S201).

  If the name resolution control unit 260-2 determines that the domain name that matches the name resolution target domain name (the domain name of the information server 520) is not stored in the domain name item of the Phase1 table 232-2 (Step S1). (S202—NO), the name resolution control unit 260-2 determines that the name resolution target domain name is not subject to Phase 1 processing, and proceeds to Phase 2.

  On the other hand, if the name resolution control unit 260-2 determines that the domain name matching the name resolution target domain name is stored in the domain name item of the Phase1 table 232-2 (step S202—YES), Phase1. The processing unit 252-2 reads out the Phase1 record of the primary DNS server address and the secondary DNS server address corresponding to the domain name that matches the name resolution request domain name from the Phase1 table 232-2 (step S211).

  Then, the name resolution request packet (IPv4, A,...) Received from the client device 100 by the IPv4 DNS resolver 291-2 for the primary DNS address and the secondary DNS address included in the Phase1 record read by the Phase1 processing unit 252-2. The domain name of the information server 520) is transferred (step S212). The IPv4 DNS resolver 291-2 monitors a response to the transmitted name resolution request packet (step S213).

  Upon receiving the name resolution request packet, the IPv4 private DNS server 511 receives the name resolution result packet (IPv4, information corresponding to the name resolution target domain name (domain name of the information server 520) included in the received name resolution request packet. A domain name of the server 520 and an IP address of the information server 520) are generated and transmitted to the line terminating device 200-2. The IPv4 DNS resolver 291-2 of the line terminating device 200-2 receives the name resolution result packet via the IPv4 communication unit 211-2. When the IPv4 DNS resolver 291-2 receives a name resolution result packet corresponding to the name resolution request packet within a preset timeout period, the IPv4 DNS resolver 291-2 determines the response content of the name resolution result packet (step S214).

  For example, when the name resolution packet received in step S214 includes transport change notification information, the IPv4 DNS resolver 291-2 uses the name resolution request packet including the transport change notification information as it is as an IPv4 client device. 100-2 is transmitted (step S215).

  Alternatively, the IPv4 DNS resolver 291-2, for example, if the RCODE (return code) included in the name resolution packet received in step S214 is information indicating successful name resolution, the name resolution result packet is sent to the IPv4 client apparatus 100. -2 (step S216). Alternatively, the IPv4 DNS resolver 291-2 determines whether the RCODE (return code) included in the name resolution packet received in step S214 is information indicating a name resolution failure / error, or in step S213, the name resolution request packet When the response is waited but there is no response, a name resolution result packet indicating that name resolution has failed is transmitted to the IPv4 client apparatus 100-2 (step S217).

  Returning to FIG. 20, when the IPv4 DNS resolver 291-2 receives the name resolution result packet including information indicating the name resolution success, the name resolution result transmission unit 280-2 performs name resolution via the IPv4 communication unit 211-2. The result packet (IPv4, domain name of information server 520, address of information server 520) is transmitted to IPv4 client apparatus 101-2 (step S1013).

  The IPv4 DNS resolver 120-2 of the IPv4 client apparatus 100-2 receives the name resolution result packet via the IPv4 communication unit 130-2. Then, the application 110-2 reads the name resolution result address (the address of the information server 520) included in the received name resolution result packet, and transmits an IP packet to the name resolution result address (step S1014). The line terminating device 200-2 transfers the IP packet to the information server 520 (step S1015), and the information server 520 transmits a response IP packet to the received IP packet (step S1016). The line terminating device 200-2 transfers the response IP packet to the IPv4 client device 100-2 (step S1017).

  Here, the name resolution processing time by the line termination device 200-2, that is, from when the line termination device 200-2 receives the name resolution request packet to when the name resolution result packet is transmitted to the IPv4 client device 100-2. This time needs to be shorter than the timeout time of the IPv4 DNS resolver 121-2. This is because the normal timeout time is set in the IPv4 DNS resolver 121-2, so even after the resolver times out, the line termination device 200-2 responds to the IPv4 DNS resolver 121-2 with the IPv4 DNS resolver 121-2. Since the resolver 121-2 cannot capture the name resolution result packet, it needs to respond faster than this.

  In step S202, when the name resolution control unit 260-2 determines whether or not the Phase1 record corresponding to the name resolution target domain name exists in the Phase1 table 232-2, the name resolution target domain name Only the Phase 1 record that completely matches the name may be determined, or the name resolution target domain name that is the subdomain name of the Phase 1 record may be determined. In this case, for example, if the name resolution target domain name is “bbb.aaa.com” and there is a Phase1 record that stores “aaa.com” in the DNS server address field, the name resolution target domain name is It is determined that the corresponding Phase1 record exists.

In this way, by making the name resolution request from the client device 100 transparent, even if load distribution is performed by DNS round robin on the DNS server side, the name resolution request is not affected without affecting the effect. It can be performed. Here, the transmission type means that the line termination device 200 does not change the content of a query such as single A or quad A first. Second, the line termination apparatus 200 does not cache the name resolution result. Note that the second is not applied in the Phase 0 process.
As described above, the line terminating device 200 may provide only a function of selecting a plurality of inquiry destinations in name resolution, and may not perform operations such as caching.

  As described above, according to the present embodiment, in order to perform name resolution of a domain name belonging to a special domain, a DNS server capable of performing name resolution of a special domain name predetermined in the circuit terminating device 200-2 is provided. Since the line terminator 200 performs the name resolution on behalf of the line terminator 200-2, the line terminator 200-2 can efficiently and optimally send the name resolution packet to the DNS server on the network without sending it to the DNS server on the network. Name resolution requests can be made.

  For example, when a specific ISP or the like wants to provide a content providing service only to the ISP user, an information providing server is installed on a network (closed network) accessible only by the ISP user, and the information providing server The domain name is generally designated as a dedicated domain name (either global or local). If this domain name is resolved to a DNS server on the Internet, the name can be resolved if it is a global domain, but if it is not accessed from within a specific provider's network, it will be resolved to the server with that address. There is no packet reachability. If it is a local domain, name resolution itself cannot be performed. Such a special domain needs to make an inquiry to a DNS server installed on the ISP network in which the server providing the service is installed.

  In addition, in a closed network (LAN) used in a specific corporate body or home, when a domain definition is made independently (privately), the defined organization or individual needs to resolve the name, It is necessary to prepare a name resolution mechanism. According to the present embodiment, it is possible to select an appropriate DNS server for such name resolution for a special domain. In addition to name resolution, consideration is given to the establishment of subsequent communications.

<Third Embodiment: Phase 2: Special Domain>
In the third embodiment, an operation example in which the name resolution processing in the network corresponding to the type B illustrated in FIG. 14 is performed by the Phase2 processing unit 253-2 will be described. In the third embodiment, the IPv4 client apparatus 100-2 that performs IPv4 communication transmits an IP packet using the information server 520 that can be connected only via the IPv4 private network 501 as a destination address. Here, the line terminating device 200-2 relays information communication from the IPv4 client device 100-2 to the information server 520. The name resolution of the domain name of the information server 520 is performed by the IPv4 DNS server 311.

FIG. 22 is a sequence diagram illustrating an operation example in which the line terminating device 200-2 according to the present embodiment relays communication from the IPv4 client device 100-2. Hereinafter, with reference to FIG. 22, an operation example of communication processing in the present embodiment will be described.
First, the user inputs the domain name of the information server 520 as destination information via the input unit provided in the IPv4 client apparatus 100-2. The application 110-2 transmits the input domain name of the information server 520 to the IPv4 DNS resolver 120-2. Then, the IPv4 DNS resolver 120-2 generates a name resolution request packet (IPv4, A, domain name of the information server 520) and transmits it to the line terminating device 200-2 (step S1020).

  When the name resolution request receiving unit 270-2 of the line termination device 200-2 receives the name resolution request packet (IPv4, A, domain name of the information server 520) via the IPv4 communication unit 211-2, the name First, the resolution control unit 260-2 performs Phase 0 determination processing for determining whether or not the name resolution processing of the received name resolution request packet is performed by the Phase 0 processing unit 251-2.

  If the name resolution control unit 260-2 determines not to perform name resolution in Phase 0 in the Phase 0 determination process in Step S100 described above, the name resolution control unit 260-2 performs name resolution in the Phase 1 processing unit 252-2. A Phase 1 determination process for determining whether or not to perform the process is performed. If the name resolution control unit 260-2 determines that name resolution is not performed in Phase 1, the name resolution control unit 260-2 determines whether or not name resolution processing is performed in the Phase 2 processing unit 253-2. Phase 2 determination processing is performed. Here, the processing in steps S1021 and S1022 in which the line termination device 200-2 acts as a proxy for name resolution will be described in detail with reference to FIG.

  First, the name resolution control unit 260-2 reads all the logical IF records stored in the logical IF storage unit 233 (step S301). Then, the name resolution control unit 260-2 determines that the logical IF record whose logical IF state item of the read logical IF record is “active” is a logical IF record indicating an available logical IF. Here, if the name resolution control unit 260 cannot detect an available logical IF record, the name resolution control unit 260 determines not to perform name resolution in Phase 2 (step S302—NO), Proceed to Phase3.

  On the other hand, if the name resolution control unit 260-2 detects a logical IF record that can be used from the logical IF storage unit 233-2 (YES in step S302), the Phase2 processing unit 253-2 sets the IPv4 DNS resolver 291-2. Then, the name resolution request packet is transferred to the DNS server address indicating the highest priority among the available logical IF records (step S312).

  The IPv4 DNS resolver 291-2 monitors a response to the name resolution request packet transferred and transmitted in step S312 (step S313). Then, when the IPv4 DNS resolver 291-2 receives a name resolution result packet corresponding to the name resolution request packet within a preset timeout period, the IPv4 DNS resolver 291-2 determines the response content of the name resolution result packet (step S314).

  For example, when the name resolution packet received in step S314 includes transport change notification information, the IPv4 DNS resolver 291-2 uses the name resolution request packet including the transport change notification information as it is as an IPv4 client device. It transmits to 100-2 (step S315).

  Alternatively, for example, if the RCODE (return code) included in the name resolution packet received in step S314 is information indicating successful name resolution, the IPv4 DNS resolver 291-2 sends the name resolution result packet to the IPv4 client apparatus 100. -2 (step S316). Alternatively, the IPv4 DNS resolver 291-2 waits for a response of the name resolution request packet in step S313, but there is no response, or the RCODE (return code) included in the name resolution packet received in step S314 is a name resolution failure / If it is information indicating an error, a name resolution result packet indicating that name resolution has failed is transmitted to the IPv4 client apparatus 100-2 (step S317).

  In step S312, when a name resolution request packet is transmitted to the DNS server on the logical IF and a plurality of name resolution result packets are received in step S314, which name resolution packet is to be adopted is the most. The name resolution result packet received earlier may be employed, or may be employed based on priority.

  As described above, according to the name resolution by the Phase 2 processing unit 253-2, when there are a plurality of routes (routes) connected to the Internet or when there are a plurality of routes reaching the site to be connected, which route Can efficiently determine whether to perform name resolution. If the name resolution in Phase 0 and Phase 1 is not achieved, the name resolution target domain name can be recognized as a global domain name belonging to the global domain, so that the name resolution can be performed by the Phase 2 process described above.

  Here, when there are a plurality of routes, name resolution is performed regardless of which route is thrown, but it is not permitted in manners to throw name resolution request packets simultaneously for all routes. According to the Phase 2 processing unit 253-2, the name resolution request packet can be transferred based on a predetermined priority order. Also, not all routes are communicable (sessions are established) (in some cases, not all are connected and there is no packet reachability to the Internet). If the priority route cannot be communicated, a name resolution request packet is transmitted to the next priority route.

  In this way, the Phase 2 processing unit 253-2 performs name resolution when connecting to a site on the Internet such as a global domain via an ISP. In addition, even when the ISP has a special domain, if only one ISP is connected to the IPv4 client apparatus 100-2, name resolution in Phase 2 is possible without setting Phase 1. It is.

<Fourth embodiment: Phase 3>
In the fourth embodiment, when the line termination device 200-2 cannot find a DNS server in the name resolution processing by the Phase 0 processing unit 251-2, Phase 1 processing unit 252-2, and Phase 2 processing unit 252-2, An operation example of the line termination device 200-2 in which name resolution processing is performed by the Phase3 processing unit 254-2 will be described.

As in the third embodiment, the name resolution request packet (IPv4, A, domain name of the information server 520) transmitted from the IPv4 DNS resolver 120-2 is sent to the name resolution request receiving unit 270- of the line terminating device 200-2. 2 is received via the IPv4 communication unit 211-2.
FIG. 24 is a flowchart illustrating an example of operation performed by the name resolution control unit 260 to determine which processing unit included in the name resolution proxy unit 250 performs name resolution.

  When the name resolution request receiving unit 270-2 receives the name resolution request packet, the name resolution control unit 260 detects the name resolution target domain name that is the domain name of the name resolution request target from the name resolution request packet. Then, the name resolution control unit 260-2 performs format check processing for the detected name resolution target domain name. Here, the format check process is performed, for example, whether or not a prohibited character predetermined in the domain name information is used, or whether or not the length of the character string of the domain name information is within a predetermined range. Such a determination process is performed (step S10).

  Then, the name resolution control unit 260-2 performs Phase 0 determination processing for determining whether or not the name resolution target domain name is subjected to name resolution processing by the Phase 0 processing unit 251-2 (step S100). If the name resolution control unit 260-2 determines that the name resolution processing of the Phase 0 processing unit 251-2 is to be performed (step S100-YES), the Phase 0 processing unit 251-2 performs name resolution processing for the name resolution target domain name. A phase 0 process is performed (step S110).

  On the other hand, when the name resolution control unit 260-2 determines not to perform the name resolution processing of the Phase 0 processing unit 251-2 in step S100 (step S100-NO), the name resolution control unit 260-2 Phase 1 determination processing is performed to determine whether or not the name resolution processing is performed on the resolution target domain name by the Phase 1 processing unit 252-2 (step S200). If the name resolution control unit 260-2 determines that the name resolution processing of the Phase1 processing unit 252-2 is performed (step S200-YES), the Phase1 processing unit 252-2 performs the Phase1 processing for the name resolution target domain name. (Step S210).

  On the other hand, when the name resolution control unit 260-2 determines not to perform the name resolution processing of the Phase1 processing unit 252-2 in step S200 (step S200-NO), the name resolution control unit 260 determines the name resolution target. Phase 2 determination processing for determining whether or not the name resolution processing is performed on the domain name by the Phase 2 processing unit 253-2 is performed (step S300). When the name resolution control unit 260-2 determines that the Phase 2 determination process of the Phase 2 processing unit 253-2 is to be performed (step S300-YES), the Phase 2 processing unit 253-2 performs the Phase 2 process for the name resolution target domain name. This is performed (step S310).

  On the other hand, if it is determined in step S300 that the name resolution control unit 260-2 does not perform the name resolution process of the Phase2 processing unit 253-2 (NO in step S300), the name resolution control unit 260-2 Phase 3 determination processing is performed to determine whether or not the name resolution processing is performed on the resolution target domain name by the Phase 3 processing unit 254-2 (step S400). When the name resolution control unit 260-2 determines that the name resolution processing of the Phase 3 processing unit 254-2 is to be performed (step S400-YES), the Phase 3 processing unit 254-2 performs Phase 3 processing on the name resolution target domain name. This is performed (step S410). On the other hand, if the name resolution control unit 260-2 determines not to perform the name resolution processing of the Phase3 processing unit 254-2 in step S300 (step S400-NO), the name resolution control unit 260-2 Generate resolution error information and end the process.

  FIG. 25 is a flowchart illustrating an operation example of the line termination device 200-2 regarding Phase 3 processing in step S400. The line terminating device 200-2 operates the DHCP client unit 245-2 in advance and acquires the address of the DNS server when the own device is activated. Furthermore, when the Phase 3 processing is performed, if there is a DHCP means (DHCP client unit 245-2) (step S401-YES) and the DNS server address cannot be acquired or is invalid, the DNS server address is again obtained by the DHCP operation. Try to get. That is, the DHCP client unit 245-2 receives the IP address of the DNS server from the DHCP server via the communication unit 210-2 (step S411).

  In addition, the Phase 3 processing unit 254-2, when the line terminating device 200-2 does not include the DHCP client unit 245-2 or cannot obtain the DNS server IP address by DHCP (step S401-NO). For example, the DNS server IP address stored in advance is acquired as the DNS server IP address at the time of shipment (step S402—YES).

  Then, the Phase3 processing unit 254-2 transmits a name resolution request packet to the DNS server IP address acquired by the DHCP client unit 245-2 via the DNS resolver 290-2 (step S412). The DNS resolver 290-2 monitors a response to the transmitted name resolution request packet (step S433). When the DNS resolver 290-2 receives a name resolution result packet corresponding to the name resolution request packet within a preset timeout period, the DNS resolver 290-2 determines the response content of the name resolution result packet (step S414).

  For example, when the name resolution result packet received in step S414 includes transport change notification information, the DNS resolver 290-2 uses the name resolution request packet including the transport change notification information as it is as the client device. 100 (step S415).

  Alternatively, for example, if the RCODE (return code) included in the name resolution packet received in step S414 is information indicating successful name resolution, the DNS resolver 290-2 sends the name resolution result packet to the client apparatus 100. Transmit (step S416). Alternatively, the DNS resolver 290-2 waits for a response of the name resolution request packet in step S413, but there is no response, or the RCODE (return code) included in the name resolution packet received in step S414 is a name resolution failure / If it is information indicating an error, a name resolution result packet indicating that the name resolution has failed is transmitted to the client device 100 (step S417).

As described above, according to the name resolution by the Phase3 processing unit 254, even when there is no route connected to the Internet, the IP address of the DNS server that can perform name resolution can be acquired from the connected network.
That is, in Phase 0 to Phase 2, if the DNS server that can be successfully resolved can be identified but there is no reachability to the DNS server (there is no route, no session is established), the name by Phase 3 A solution is attempted.

  That is, when the network is viewed from the IPv4 client apparatus 100-2, it is not known what the state of the network is, what kind of configuration it is, and how it can be connected to the network (when starting up or when it is not yet set up). The Phase 3 processing unit 254-2 provided in the client device 100-2 acquires network information.

  In this way, in the Phase 3 process, the DNS server address is notified from a relay device such as a higher-level router that is reliably connected by the DHCP function. This generally operates automatically when an IP appliance such as the line terminating device 200 is connected to the network.

  If there is no DHCP function, the DNS server address is set in advance. Furthermore, even when the Phase3 setting change (DNS server address change) is performed, it is necessary that the client device can return to the DNS server address acquisition by DHCP alone. This is because it is not guaranteed that the changed DNS server can reliably perform name resolution. On the contrary, the DNS server address notified by DHCP needs to be a server address that can always perform reliable name resolution.

<Fifth Embodiment>
In the fifth embodiment, an operation example in which the name resolution process in the network corresponding to the type C illustrated in FIG. 14 is performed by the Phase 2 processing unit 253-2 of the line termination device 200-2 will be described. In the fifth embodiment, an IPv4 client apparatus 100-2 that performs communication using IPv4 transmits an IP packet using the information server 521 connected to the Internet as a destination address. Here, the line terminating device 200-2 relays information communication from the IPv4 client device 100-2 to the information server 521. The name resolution of the domain name of the information server 521 is performed by the IPv4 DNS server 311.

FIG. 26 is a sequence diagram illustrating an operation example in which the line terminating device 200-2 according to the present embodiment relays communication from the IPv4 client device 100-2. Hereinafter, with reference to FIG. 26, an operation example of communication processing in the present embodiment will be described.
First, the IPv4 client apparatus 100-2 transmits a name resolution request packet (IPv4, A, domain name of the information server 521) to the line terminating apparatus 200-2 (step S1030).

  The line terminating device 200-2 transmits the received name resolution request packet to the IPv4 DNS server 311 by, for example, the Phase2 processing unit 253-2 (step S1031). The line terminating device 200-2 receives the name resolution result packet (IPv4, the domain name of the information server 521, the IP address of the information server 521) returned from the IPv4 DNS server 311 (step S1032), and the IPv4 client device 100. -2 (step S1033).

The IPv4 client device 100-2 reads the name resolution result IP address from the received name resolution result packet, and transmits an IP packet (IPv4) with the read name resolution result IP address as the destination (step S1034). The line terminating device 200-2 transfers the IP packet to the information server 521 (step S1035), and the information server 521 sends a response IP packet (IPv4) to the line terminating device 200-2 in response to the received IP packet. (Step S1036). The line terminating device 200-2 transfers the received response IP packet to the IPv4 client device 100-2. The IPv4 client device 100-2 receives the response IP packet (step S1037).
Thus, according to the present embodiment, the Internet connection in IPv4 is relayed.

<Sixth Embodiment>
In the sixth embodiment, an example of operation in which the name resolution process in the network corresponding to the type D shown in FIG. In the sixth embodiment, an IPv6 client apparatus 101-2 that performs communication using IPv6 transmits an IP packet using the information server 522 connected to the IPv6 private network 502 as a destination address. Here, the line terminating device 200-4 relays information communication from the IPv6 client device 101-2 to the information server 522. The name resolution of the domain name of the information server 522 is performed by the IPv6 private DNS server 512.

FIG. 27 is a sequence diagram illustrating an operation example in which the line terminating device 200-4 according to the present embodiment relays communication from the IPv6 client device 101-2. Hereinafter, with reference to FIG. 27, an operation example of the communication processing in the present embodiment will be described.
First, the IPv6 client apparatus 101-2 transmits a name resolution request packet (IPv6, AAAA, information server 522 domain name) to the line terminating apparatus 200-4 (step S1040).

  The line terminating device 200-4 transmits the received name resolution request packet to, for example, the IPv6 private DNS server 512 by the Phase 0 processing unit 251-4 (step S1041). The line terminating device 200-4 receives the name resolution result packet (IPv6, domain name of the information server 522, IP address of the information server 522) returned from the IPv6 private DNS server 512 (step S1042), and receives an IPv6 client. It transmits to the apparatus 101-2 (step S1043).

The IPv6 client apparatus 101-2 reads the name resolution result IP address from the received name resolution result packet, and transmits an IP packet (IPv6) with the read name resolution result IP address as the destination (step S1044). The line termination device 200-4 transfers the IP packet to the information server 522 (step S1045), and the information server 522 sends a response IP packet (IPv6) to the line termination device 200-4 in response to the received IP packet. (Step S1046). The line terminating device 200-4 transfers the received response IP packet to the IPv6 client device 101-2. The IPv6 client device 101-2 receives the response IP packet (step S1047).
Thus, according to the present embodiment, the closed connection in IPv6 is relayed.

<Seventh Embodiment>
In the seventh embodiment, an operation example in which the name resolution processing in the network corresponding to the type E illustrated in FIG. 14 is performed by the Phase 2 processing unit 253-4 of the line termination device 200-4 will be described. In the seventh embodiment, the IPv6 client apparatus 101-2 that performs IPv6 communication transmits an IP packet using the information server 525 connected to the IPv6 private network 502 as a destination address. Here, the line termination device 200-4 relays information communication from the IPv6 client device 101-2 to the information server 525. In the present embodiment, the name resolution of the domain name of the information server 525 is performed by the IPv6 DNS server 312. This name resolution can also be performed by the IPv6 private DNS server 512.

FIG. 28 is a sequence diagram illustrating an operation example in which the line terminating device 200-4 according to the present embodiment relays communication from the IPv6 client device 101-2. Hereinafter, with reference to FIG. 28, an operation example of communication processing in the present embodiment will be described.
First, the IPv6 client apparatus 101-2 transmits a name resolution request packet (IPv6, AAAA, information server 525 domain name) to the line terminating apparatus 200-4 (step S1050).

  The line terminating device 200-4 transmits the received name resolution request packet to the IPv6 DNS server 312 by, for example, the Phase2 processing unit 253-4 (step S1051). The line terminating device 200-4 receives the name resolution result packet (IPv6, the domain name of the information server 525, the IP address of the information server 525) returned from the IPv6 DNS server 312 (step S1052), and the IPv6 client device 101. -2 (step S1053).

The IPv6 client apparatus 101-2 reads the name resolution result IP address from the received name resolution result packet, and transmits an IP packet (IPv6) with the read name resolution result IP address as the destination (step S1054). The line termination device 200-4 transfers the IP packet to the information server 525 (step S1055), and the information server 525 sends a response IP packet (IPv6) to the line termination device 200-4 in response to the received IP packet. (Step S1056). The line terminating device 200-4 transfers the received response IP packet to the IPv6 client device 101-2. The IPv6 client device 101-2 receives the response IP packet (step S1057).
Thus, according to the present embodiment, communication to the special domain in IPv6 is relayed.

<Eighth Embodiment>
In the eighth embodiment, an operation example in which the name resolution processing in the network corresponding to the type F illustrated in FIG. 14 is performed by the Phase 2 processing unit 253-4 of the line termination device 200-4 will be described. In the eighth embodiment, an IPv6 client apparatus 101-2 that performs communication using IPv6 transmits an IP packet using the information server 523 connected to the IPv6 private network 502 as a destination address. Here, the line termination device 200-4 relays information communication from the IPv6 client device 101-2 to the information server 523. The name resolution of the domain name of the information server 523 is performed by the IPv6 DNS server 312.

FIG. 29 is a sequence diagram illustrating an operation example in which the line terminating device 200-4 according to the present embodiment relays communication from the IPv6 client device 101-2. Hereinafter, with reference to FIG. 29, an operation example of communication processing in the present embodiment will be described.
First, the IPv6 client apparatus 101-2 transmits a name resolution request packet (IPv6, AAAA, information server 523 domain name) to the line terminating apparatus 200-4 (step S1060).

  The line terminating device 200-4 transmits the received name resolution request packet to the IPv6 DNS server 312 by, for example, the Phase1 processing unit 252-4 (step S1061). The line terminating device 200-4 receives the name resolution result packet (IPv6, the domain name of the information server 523, the IP address of the information server 523) returned from the IPv6 DNS server 312 (step S1062), and the IPv6 client device 101. -2 (step S1063).

The IPv6 client apparatus 101-2 reads the name resolution result IP address from the received name resolution result packet, and transmits an IP packet (IPv6) with the read name resolution result IP address as the destination (step S1064). The line termination device 200-4 transfers the IP packet to the information server 523 (step S1065), and the information server 523 sends a response IP packet (IPv6) to the line termination device 200-4 in response to the received IP packet. (Step S1066). The line terminating device 200-4 transfers the received response IP packet to the IPv6 client device 101-2. The IPv6 client device 101-2 receives the response IP packet (step S1067).
As described above, according to the present embodiment, communication to the global domain in IPv6 is relayed.

<Ninth Embodiment>
In the ninth embodiment, an operation example in which the name resolution processing in the network corresponding to the type H illustrated in FIG. 14 is performed by the Phase 0 processing unit 251-4 of the line termination device 200-4 will be described. In the ninth embodiment, the IPv6 client apparatus 101-2 that performs IPv6 communication transmits an IP packet using the information server 521 connected to the IPv4 Internet 301 as a destination address. Here, the line terminating device 200-4 relays information communication from the IPv6 client device 101-2 to the information server 521. The name resolution of the domain name of the information server 521 is performed by the IPv6 DNS server 312.

FIG. 30 is a sequence diagram illustrating an operation example in which the line terminating device 200-4 according to the present embodiment relays communication from the IPv6 client device 101-2. Hereinafter, with reference to FIG. 30, an operation example of communication processing in the present embodiment will be described.
First, the IPv6 client apparatus 101-2 transmits a name resolution request packet (IPv6, AAAA, information server 521 domain name) to the line terminating apparatus 200-4 (step S1070).

  The line terminating device 200-4 transmits the received name resolution request packet to the IPv6 DNS server 312 by, for example, the Phase 0 processing unit 251-4 (step S1071). Upon receiving the name resolution result packet (IPv6, domain name of the information server 521, IP address of the information server 521) received from the IPv6 DNS server 312 (step S1072), the line terminating device 200-4 receives the IPv6 client device 101. -2 (step S1073).

  The IPv6 client apparatus 101-2 reads the name resolution result IP address from the received name resolution result packet, and transmits an IP packet (IPv6) with the read name resolution result IP address as the destination (step S1074). The IP header conversion unit 220-4 of the line terminating device 200-4 converts the IP packet (IPv6) into an IP packet based on IPv4 (step S1075) and transfers the packet to the information server 521 via the IPv4 closed network 900 ( Step S1076).

In response to the received IP packet, the information server 521 transmits a response IP packet (IPv4) to the line terminating device 200-4 (step S1077). The IP header conversion unit 220-4 of the line termination device 200-4 converts the received response IP packet (IPv4) into an IPv6 packet (step S1078), and transfers the packet to the IPv6 client device 101-2. The IPv6 client device 101-2 receives the response IP packet (step S1079).
As described above, according to the present embodiment, communication from a client device capable of communication using only IPv6 to a service provided using only IPv4 is relayed.

<Tenth Embodiment>
In the tenth embodiment, an operation example in which the name resolution processing in the network corresponding to the type I shown in FIG. 14 is performed by the Phase 0 processing unit 251-2 of the line termination device 200-2 will be described. In the tenth embodiment, an IPv4 client apparatus 100-2 that performs IPv4 communication transmits an IP packet using the information server 523 connected to the IPv6 Internet 302 as a destination address. Here, the line terminating device 200-2 relays information communication from the IPv4 client device 100-2 to the information server 523. Further, the name resolution of the domain name of the information server 523 is performed by the IPv4 DNS server 311.

FIG. 31 is a sequence diagram illustrating an operation example in which the line terminating device 200-2 according to the present embodiment relays communication from the IPv4 client device 100-2. Hereinafter, with reference to FIG. 31, an operation example of communication processing in the present embodiment will be described.
First, the IPv4 client apparatus 100-2 transmits a name resolution request packet (IPv4, AA, domain name of the information server 523) to the line terminating apparatus 200-2 (step S1080).

  The line terminating device 200-2 transmits the received name resolution request packet to the IPv4 DNS server 311 by, for example, the Phase 0 processing unit 251-2 (step S1081). Upon receiving the name resolution result packet (IPv4, the domain name of the information server 523, the IP address of the information server 523) returned from the IPv4 DNS server 311 (step S1082), the line terminating device 200-2 receives the IPv4 client device 100. -2 (step S1083).

  The IPv4 client apparatus 100-2 reads the name resolution result IP address from the received name resolution result packet, and transmits an IP packet (IPv4) with the read name resolution result IP address as the destination (step S1084). The IP header conversion unit 220-2 of the line terminating device 200-2 converts the IP packet (IPv4) into an IP packet based on IPv6 (step S1085), and transfers it to the information server 523 via the IPv6 closed network 901 ( Step S1086).

In response to the received IP packet, the information server 523 transmits a response IP packet (IPv6) to the line terminating device 200-2 (step S1087). The IP header conversion unit 220-2 of the line terminating device 200-2 converts the received response IP packet (IPv6) into an IPv4 packet (step S1078), and transfers the packet to the IPv4 client device 100-2. The IPv4 client device 100-2 receives the response IP packet (step S1089).
As described above, according to the present embodiment, communication from a client device capable of communication only by IPv4 to a service provided only by IPv6 is relayed.

<Eleventh embodiment>
In the eleventh embodiment, an example of operation in which the name resolution processing in the network corresponding to the type J shown in FIG. 14 is performed by the Phase 0 processing unit 251-3 of the line terminating device 200-3 will be described. In the eleventh embodiment, an IPv6 client apparatus 101-1 that performs IPv6 communication transmits an IP packet using the information server 521 connected to the IPv4 Internet 301 as a destination address. Here, the line terminating device 200-3 relays information communication from the IPv6 client device 101-1 to the information server 521. The name resolution of the domain name of the information server 521 is performed by the IPv4 DNS server 311.

FIG. 32 is a sequence diagram illustrating an operation example in which the line terminating device 200-3 according to the present embodiment relays communication from the IPv6 client device 101-1. Hereinafter, with reference to FIG. 32, an operation example of the communication processing in the present embodiment will be described.
First, the IPv6 client apparatus 101-1 transmits a name resolution request packet (IPv6, AAAA, information server 521 domain name) to the line terminating apparatus 200-3 (step S1090).

  The line terminating device 200-3 transmits the received name resolution request packet to the IPv4 DNS server 311 by, for example, the Phase 0 processing unit 251-3 (step S1091). Upon receiving the name resolution result packet (IPv4, domain name of the information server 521, IP address of the information server 521) received from the IPv4 DNS server 311 (step S1092), the line terminating device 200-3 receives the IPv6 client device 101. -1 (step S1093).

  The IPv6 client apparatus 101-1 reads the name resolution result IP address from the received name resolution result packet, and transmits an IP packet (IPv6) with the read name resolution result IP address as the destination (step S1094). The IP header conversion unit 220-3 of the line terminating device 200-3 converts the IP packet (IPv6) into an IP packet based on IPv4 (step S1095), and transfers it to the information server 521 (step S1096).

In response to the received IP packet, the information server 521 transmits a response IP packet (IPv4) to the line terminating device 200-3 (step S1097). The IP header conversion unit 220-3 of the line terminating device 200-3 converts the received response IP packet (IPv4) into an IPv6 packet (step S1098), and transfers the packet to the IPv6 client device 101-1. The IPv6 client apparatus 101-1 receives the response IP packet (step S1099).
As described above, according to the present embodiment, communication from a client device capable of communication using only IPv6 to a service provided using only IPv4 is relayed.

  Note that the communication apparatus according to the present invention may include the functional blocks of the IPv4 client apparatus 100-1 and the line termination apparatus 200-1 in the same terminal, like the communication apparatus 201 shown in FIG. . Each functional unit 32 shown in FIG. 33 has the same configuration as each functional unit having the same name provided in the IPv4 client device 100-1 and the line terminating device 200-1. Further, the IPv6 client device 101-1 and the line termination device 200-1 may be provided in the same terminal.

  As shown in FIG. 34, the Phase 0 table stored in the Phase 0 table 231 includes both a combination of a virtual address based on IPv4 and a real address based on IPv6, and a combination of a virtual address based on IPv6 and a real address based on IPv4. May be stored. For example, in the Phase 0 record in FIG. 34A, an IPv4 virtual address is assigned to the domain name. Here, when a single A name resolution request is received with a domain name of “aaa.bbb.ccc”, an IPv6 address corresponding to “aaa.bbb.ccc” is acquired by the Phase 0 processing unit 251-1. The real address information is updated and stored.

  In FIG. 34E, an IPv6 virtual address is assigned to the same domain name as in FIG. Here, when a quad A name resolution request is received with the domain name “aaa.bbb.ccc”, the Phase 0 processing unit 251-1 acquires an IPv64 address corresponding to “aaa.bbb.ccc”. The real address information is updated and stored.

When a name resolution request for the domain name “abcd.efgh.com” is received, if it is a single A, a virtual address (IPv4) is returned with reference to FIG. In the case of quad A, there is no record in the Phase 0 table 231, so the phase 1 processing is started.
When the name resolution request for the domain name “mmm.nnn.ooo” is received, if it is quad A, the virtual address (IPv6) is returned with reference to FIG. In the case of single A, there is no record in the Phase 0 table 231, so the phase 1 processing is started.

  In addition, the configuration according to the present embodiment can distribute the load of communication via the network. For example, it is possible to distribute the load by setting the access to the plurality of service providing servers having the same FQDN “xxx.yyy.zzz” stored in the Phase 1 processing unit 252 in advance.

  That is, there may be a plurality of service providing servers having a domain name (FQDN) of “xxx.yyy.zzz”. For example, even if the functions of a plurality of servers are the same, if the data range and operation that can be handled are different, there is a case where it is necessary to continuously access the same server because session management is required. In this case, DNS round robin cannot be used, but this application can handle it.

  That is, the name resolution destination is fixed by setting the DNS server address of the domain name resolution destination in the Phase 1 processing unit 252. By fixing the address returned by each DNS server, the service providing server and the IP appliance can be fixedly linked. Thereby, since the number of IP appliances to which the service providing server corresponds can be limited, it is possible to always keep the number of IP appliances below the processing capability as the service providing server.

  As described above, according to the communication apparatus of the present invention, the name from the DNS resolver connected to a plurality of IP networks while maintaining the usability of the conventional IP network connection (eg, Internet connection, LAN connection, etc.). It is possible to provide a mechanism for determining whether name resolution can be performed by transmitting a resolution request to a DNS server on which of a plurality of IP networks.

  It should be noted that a program for realizing the function of the processing unit in the present invention is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed for communication. Also good. The “computer system” here includes an OS and hardware such as peripheral devices. The “computer system” includes a WWW system having a homepage providing environment (or display environment). The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Further, the “computer-readable recording medium” refers to a volatile memory (RAM) in a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding programs for a certain period of time are also included.

  The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

1 is a diagram illustrating a network environment according to an embodiment of the present invention. FIG. FIG. 4 is a diagram illustrating a special domain according to an embodiment of the present invention. It is a figure which shows the communication apparatus by one Embodiment of this invention. It is a figure which shows the data structure of the Phase0 table by one Embodiment of this invention. It is a figure which shows the data structure of the Phase1 table by one Embodiment of this invention. It is a figure which shows the data structure of the logic IF memory | storage part by one Embodiment of this invention. It is a figure which shows the communication apparatus by one Embodiment of this invention. It is a figure which shows the communication apparatus by one Embodiment of this invention. It is a figure which shows the communication apparatus by one Embodiment of this invention. FIG. 3 illustrates an IPv4 client device according to an embodiment of the present invention. FIG. 3 illustrates an IPv4 client device according to an embodiment of the present invention. FIG. 3 illustrates an IPv6 client device according to an embodiment of the present invention. FIG. 3 illustrates an IPv6 client device according to an embodiment of the present invention. It is the figure which classified the network form which a communication apparatus relays communication by one Embodiment of this invention. It is the figure which classified the network form which a communication apparatus relays communication by one Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the type G network form is relayed by the 1st Embodiment of this invention. It is a flowchart which shows the process regarding Phase0 by the 1st Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the type G network form is relayed by the 1st Embodiment of this invention. It is a flowchart which shows the process regarding Phase0 by the 1st Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the network form of type A is relayed by the 2nd Embodiment of this invention. It is a flowchart which shows the process regarding Phase1 by the 2nd Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the network form of type B is relayed by the 3rd Embodiment of this invention. It is a flowchart which shows the process regarding Phase3 by the 3rd Embodiment of this invention. It is a flowchart which shows the process regarding Phase3 by the 4th Embodiment of this invention. It is a flowchart which shows the process regarding Phase3 by the 4th Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the network form of the type C is relayed by the 5th Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the network form of the type D is relayed by the 6th Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the network form of the type E is relayed by the 7th Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the network form of the type F is relayed by the 8th Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the network form of type H is relayed by the 9th Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the type I network form is relayed by the 10th Embodiment of this invention. It is a sequence diagram which shows the operation example by which the communication of the network form of the type J is relayed by the 11th Embodiment of this invention. It is a figure which shows the communication apparatus by one Embodiment of this invention. It is a figure which shows the data structure of the Phase0 table by one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Route server 11 DNS server 100-1 IPv4 client apparatus 101-1 IPv6 client apparatus 110-1 Application 111-1 Application 120-1 IPv4 DNS resolver 121-1 IPv6 DNS resolver 130-1 IPv4 communication part 131-1 IPv6 communication part 100- 2 IPv4 client device 101-2 IPv6 client device 110-2 application 111-2 application 120-2 IPv4 DNS resolver 121-2 IPv6 DNS resolver 130-2 IPv4 communication unit 131-2 IPv6 communication unit 200-1 line termination device 201-1 communication Device 210-1 Communication unit 211-1 IPv4 communication unit 212-1 IPv6 communication unit 220-1 IP header conversion unit 230- Storage unit 231-1 Phase 0 table 232-1 Phase 1 table 233-1 Logical IF storage unit 240-1 Corresponding information update unit 241-1 Controlled unit 242-1 Logical IF control unit 245-1 DHCP client unit 246-1 DHCP server Unit 250-1 name resolution proxy unit 251-1 Phase 0 processing unit 252-1 Phase 1 processing unit 253-1 Phase 2 processing unit 254-1 Phase 3 processing unit 260-1 name resolution control unit 270-1 name resolution request receiving unit 280-1 Name resolution result transmission unit 290-1 DNS resolver 291-1 IPv4 DNS resolver 292-1 IPv6 DNS resolver 200-2 Line termination device 201-2 Communication device 210-2 Communication unit 211-2 IPv4 communication unit 212-2 IPv6 communication unit 220- 2 IP header conversion unit 230-2 storage unit 231-2 Phase 0 table 232-2 Phase 1 table 233-2 logical IF storage unit 241-2 controlled unit 242-2 logical IF control unit 245-2 DHCP client unit 246-2 DHCP server Unit 250-2 name resolution proxy unit 251-2 Phase 0 processing unit 252-2 Phase 1 processing unit 253-2 Phase 2 processing unit 254-2 Phase 3 processing unit 260-2 name resolution control unit 270-2 name resolution request receiving unit 280-2 Name resolution result transmission unit 290-2 DNS resolver 291-2 IPv4 DNS resolver 292-2 IPv6 DNS resolver 200-3 Line termination device 201-3 Communication device 210-3 Communication unit 211-3 IPv4 communication unit 212-3 IPv6 communication unit 220- IP header conversion unit 230-3 storage unit 231-3 Phase 0 table 233-3 Phase 1 table 233-3 logical IF storage unit 241-3 controlled unit 242-2 logical IF control unit 245-3 DHCP client unit 246-3 DHCP server Unit 250-3 Name resolution proxy unit 251-3 Phase 0 processing unit 252-2 Phase 1 processing unit 253-3 Phase 2 processing unit 254-3 Phase 3 processing unit 260-3 Name resolution control unit 270-3 Name resolution request receiving unit 280-3 Name resolution result transmission unit 290-3 DNS resolver 291-3 IPv4 DNS resolver 292-3 IPv6 DNS resolver 200-4 Line termination device 201-4 Communication device 210-4 Communication unit 211-4 IPv4 communication unit 212-4 IPv6 communication unit 220- IP header conversion unit 230-4 storage unit 231-4 Phase 0 table 232-4 Phase 1 table 233-4 logical IF storage unit 241-4 controlled unit 242-4 logical IF control unit 245-4 DHCP client unit 246-4 DHCP server Section 250-4 Name resolution proxy section 251-4 Phase 0 processing section 252-4 Phase 1 processing section 253-4 Phase 2 processing section 254-4 Phase 3 processing section 260-4 Name resolution control section 270-4 Name resolution request receiving section 280-4 Name resolution result transmission unit 290-4 DNS resolver 291-4 IPv4 DNS resolver 292-4 IPv6 DNS resolver 300 First network 301 IPv4 Internet 302 IPv6 Internet 310 IPv6 DNS server 311 Pv4 DNS server 312 IPv6 DNS server 320 Information server 400 Second network 410 DNS server 420 Information server 500 Third network 501 IPv4 private network 502 IPv6 private network 511 IPv4 private DNS server 512 IPv6 private DNS server 520 information server 521 information Server 523 Information server 524 Information server 525 Information server 900 IPv4 closed network 901 IPv6 closed network 911 DNS server 912 DNS server 1001 Host 1002 ISP-A network 1003 ISP-B network 1004 Private network 1005 Communication device

Claims (4)

A communication apparatus capable of IP communication that performs name resolution by any DNS server among a plurality of DNS servers provided in a network in which communication is performed according to a first network protocol and a second network protocol,
And domain name information of the accessible information server only by the second network protocol, a virtual IP address that is predetermined by the first network protocol, and the real IP address of the information server by the second network protocol First storage means for storing first correspondence information that is information associated with
A predetermined domain name information, the domain name information resolvable is information associating the DNS server IP address is the IP address of the DNS server in the second correspondence information and the second memory for storing pre Me Means,
A third correspondence information is stored that associates a predetermined priority, a predetermined DNS server IP address, and state information indicating whether communication to the DNS server IP address is valid or invalid . Storage means,
A name resolution request receiving unit for receiving first name resolution request information according to the first network protocol;
The virtual IP address of the first network and the real IP address of the second network corresponding to the domain name information included in the first name resolution request information are stored in the first storage means. For example, the virtual IP address is read and output as name resolution result information, and the virtual IP address corresponding to the domain name information is stored, but the real IP address must be stored in the first storage means. For example, the second name resolution request information including the domain name information is transmitted to the DNS server that performs name resolution using the second network protocol among the plurality of DNS servers. Upon receiving the second name resolution result information corresponding to the said domain name information, the virtual IP address of the first network The real IP address of the second network included in the second name resolution result information is stored in the first storage means, and the name resolution result information including the virtual IP address of the first network is output. A first name resolution proxy means to
With the DNS server IP address stored in the second storage means associated with the domain name information included in the first name resolution request information as the destination, the first name resolution request information is transmitted as the second name resolution request information, a second name resolution proxy means receiving and outputting the name resolution result information corresponding to the second name resolution request information,
A DNS server IP address indicating that the status information is valid and the highest priority among the third correspondence information is detected from the third storage unit, and the detected DNS server IP address is detected. The third name resolution proxy means for transferring the first name resolution request information as second name resolution request information and receiving and outputting name resolution result information corresponding to the second name resolution request information When,
Whether to perform name resolution request to the pre-stored DNS server IP address, I row name resolution by either performing name resolution request to the DNS server IP address received from the DHCP server, the first A fourth name resolution proxy means for receiving and outputting name resolution result information corresponding to the name resolution request information ;
If the domain name information included in the first name resolution request information received by the name resolution request receiving unit is stored in the first storage means, the first name resolution proxy means is operated, If the domain name information is not stored in the first storage means and the DNS server IP address corresponding to the domain name information is stored in the second storage means, the second name resolution The proxy unit is operated, the DNS server IP address corresponding to the domain name information is not stored in the second storage unit, and the DNS server IP address associated with the status information indicating validity is the third if it is in the memory means storing said third operates the name resolution proxy means, wherein the DNS server IP address associated with the state information indicating the effective third storage means If not stored, the name resolution control means for operating said fourth name resolution proxy means,
A communication apparatus comprising: When an IP packet destined for the virtual IP address of the first network according to the first network protocol is received, the virtual information of the first network is obtained from the first correspondence information stored in the first storage means. Protocol that reads the real IP address of the second network corresponding to the IP address, and converts the header information of the IP packet into the header information by the second network protocol with the IP address of the second network as the destination The communication apparatus according to claim 1, further comprising a conversion unit. There line name resolution by either the DNS server of the first network protocol and the second plurality of DNS servers network protocol and by the communication is provided to the network to be performed in, accessible only by the second network protocol and domain name information of the information server, wherein the virtual IP address that is predetermined by the first network protocol, the first correspondence is information associating the actual IP address of the information server by the second network protocol first storage means for storing information, and the domain name information to a predetermined, second, which is information associating the DNS server IP address is the IP address of resolvable DNS servers the domain name information correspondence information and the second storage means for storing pre Me, predetermined et al Priorities and a DNS server IP address predetermined third storage means for communication to the DNS server IP address storing third association information associating the state information indicating whether valid or invalid And a communication method of a communication device capable of IP communication comprising:
A name resolution request receiving unit receiving first name resolution request information according to the first network protocol;
The first name resolution proxy means includes a virtual IP address of the first network and a real IP address of the second network corresponding to domain name information included in the first name resolution request information . If it is stored in one storage means, the virtual IP address is read and output as name resolution result information, and the virtual IP address corresponding to the domain name information is stored, but the real IP address is the first If not stored in one storage means, second name resolution request information including the domain name information is transmitted to the DNS server that performs name resolution by the second network protocol among the plurality of DNS servers. When receiving the second name resolution result information corresponding to the second name resolution request information, and the domain name information, the first net The virtual IP address of the first network and the real IP address of the second network included in the second name resolution result information are stored in the first storage means, and the virtual IP address of the first network is Outputting the included name resolution result information ;
The second name resolution proxy means uses the DNS server IP address stored in the second storage means in association with the domain name information included in the first name resolution request information as the destination. Transmitting one name resolution request information as the second name resolution request information, receiving and outputting name resolution result information corresponding to the second name resolution request information;
The third name resolution proxy means detects the DNS server IP address indicating that the status information is valid and has the highest priority among the third correspondence information from the third storage means. and, the DNS server IP address detected, the first name resolution request information transferred as a second name resolution request information, receives the name resolution result information corresponding to the second name resolution request information Output step;
The fourth name resolution proxy means makes a name resolution request for a DNS server IP address stored in advance or makes a name resolution request for a DNS server IP address received from a DHCP server. resolve I rows and outputting received name resolution result information corresponding to the first name resolution request information,
If the domain name information included in the first name resolution request information received by the name resolution request receiving unit is stored in the first storage unit, the name resolution control unit may perform the first name resolution. If the proxy means is operated and the domain name information is not stored in the first storage means, and the DNS server IP address corresponding to the domain name information is stored in the second storage means , The DNS server IP address corresponding to the status information indicating that the second name resolution proxy means is operated and the DNS server IP address corresponding to the domain name information is not stored in the second storage means. if IP address is if stored in said third memory means, DNS server IP address which the third operates the name resolution proxy means, associated with the status information indicating validity Not stored in the third memory means, and operating the fourth name resolution proxy means,
A communication method comprising: When the protocol conversion means receives an IP packet destined for the virtual IP address of the first network according to the first network protocol, the protocol conversion means obtains the first correspondence information stored in the first storage means from the first correspondence information. The real IP address of the second network corresponding to the virtual IP address of the first network is read out, and the header information of the IP packet is the header according to the second network protocol destined for the IP address of the second network The communication method according to claim 3, further comprising: converting the information into information.

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