Communication device, network system, communication method and program

Abstract

A storage unit (12) stores a routing table in which a record including a destination network ID, a subnet mask, and an IP address of a gateway is registered. A table management unit (103): registers a first record in the routing table, the first record including an IP address, as the destination network ID, of a first communication device that is connected to a communication device (100) via a first communication network, a full-bit subnet mask as the subnet mask, and, as the IP address of the gateway, an IP address of a first gateway that is connected to the first communication network or identifying information of a first communication adapter; and updates the routing table so as to indicate a second path which is a path passing through a second communication network, as a default route. This configuration makes it possible to appropriately determine a communication route without troubling the user and in a simple configuration.

Description

[Technical Field]

[0001] The present disclosure relates to a communication device, a network system, a communication method, and a program. [Background technology]

[0002] In recent years, communication devices that can connect to multiple communication networks, such as mobile phone networks and wireless local area networks (LANs), have become known. Such communication devices are equipped with multiple communication adapters for connecting to the corresponding communication networks. The communication device basically uses a routing table to identify a communication adapter corresponding to a subnetwork to which a communication partner belongs, and communicates with the communication partner using the identified communication adapter.

[0003] Here, if the subnetwork to which the communication partner belongs is not registered in the routing table, a communication adapter for connecting to a default gateway is used for communication. However, there is a possibility that the communication adapter for connecting to the default gateway will not be able to connect the communication device to the subnetwork to which the communication partner belongs. Currently, various technologies are being considered to solve this problem. For example, Patent Document 1 describes a technology that uses a dummy address to determine a communication path and determines a communication adapter to be used for communication. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-333080 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology described in Patent Document 1 is a technology that deviates significantly from the implementation of TCP / IP (Transmission Control Protocol / Internet Protocol) and requires complicated processing. On the other hand, within the scope of TCP / IP implementation, a method of registering the subnet to which the communication partner belongs in a routing table is also conceivable. However, this method requires the user to identify the subnet to which the communication partner belongs, which requires a great deal of effort on the part of the user. For this reason, there is a demand for a technology that can appropriately determine a communication route with a simple configuration without requiring the user to take time and effort.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a communication device, a network system, a communication method, and a program that appropriately determine a communication path with a simple configuration without causing the user any trouble. [Means for solving the problem]

[0007] In order to achieve the above object, a communication device according to the present disclosure includes: A communication device connected to a first communication network and a second communication network, a first communications adapter for connecting to the first communications network; a second communication adapter for connecting to the second communication network; a storage means for storing a routing table in which a record including a destination network ID, a subnet mask, and an IP address of a gateway is registered; The first communication network ID is used as the destination network ID. and another communication network connected to the first communication network.and a table management means for registering in the routing table a first record which is a record including an IP address of a first communication device connected to the communication device via the first communication network, a full-bit subnet mask as the subnet mask, and an IP address of a first gateway connected to the first communication network or identification information of the first communication adapter as the gateway IP address, and updating the routing table so that the second route, out of a first route which is a route via the first communication network and a second route which is a route via the second communication network, is indicated as a default route. [Effects of the Invention]

[0008] In the present disclosure, a first record is registered in a routing table, the first record including the IP address of the first communication device as the destination network ID, the full-bit subnet mask as the subnet mask, and the IP address of the first gateway or the identification information of the first communication adapter as the gateway IP address, and the routing table is updated to indicate the second route, which is a route via the second communication network, as the default route. Therefore, according to the present disclosure, a communication route can be appropriately determined with a simple configuration without requiring the user to do any effort. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a configuration of a network system according to a first embodiment. [Figure 2] 1 is a diagram illustrating a configuration of a communication device according to a first embodiment. [Figure 3] Functional configuration diagram of a communication device according to the first embodiment [Figure 4] 1A and 1B are diagrams showing routing tables according to the first embodiment, in which (A) shows the routing table before a communication destination is added, (B) shows the routing table after a communication destination is added, and (C) shows the routing table after a default gateway is deleted. [Figure 5] 10 is a flowchart showing a table management process executed by the communication device according to the first embodiment; [Figure 6] Flowchart showing the record registration process in FIG. 5 [Figure 7] Configuration diagram of a network system according to a second embodiment [Figure 8] Functional configuration diagram of a communication device according to a second embodiment [Figure 9] A diagram showing a communication destination information registration screen [Figure 10] 10A and 10B are diagrams showing routing tables according to a second embodiment, in which (A) shows the routing table after a DNS server is added, (B) shows the routing table after a communication destination is added, and (C) shows the routing table after a default gateway is deleted. [Figure 11] 10 is a flowchart showing a table management process executed by a communication device according to a second embodiment. [Figure 12] Configuration diagram of a network system according to a third embodiment [Figure 13] 10A and 10B are diagrams showing routing tables according to a third embodiment, in which (A) shows the routing table before a communication destination is added, (B) shows the routing table after a communication destination is added, and (C) shows the routing table after a default gateway is deleted. [Figure 14] FIG. 10 is an explanatory diagram of a procedure for updating network settings in a communication device according to a fourth embodiment; [Figure 15] 10 is a flowchart showing a setting correction process executed by a communication device according to a fourth embodiment. [Figure 16] Configuration diagram of a network system according to a fifth embodiment [Figure 17] Functional configuration diagram of a communication device according to a fifth embodiment [Figure 18] FIG. 10 is an explanatory diagram of a name resolution method performed by a communication device according to a fifth embodiment; [Figure 19] 10A and 10B are diagrams showing routing tables according to a fifth embodiment, in which (A) shows the routing table after a DNS server is added, (B) shows the routing table after a communication destination is added, and (C) shows the routing table after a default gateway is deleted. [Figure 20] 13A and 13B are diagrams showing routing tables according to a sixth embodiment, in which (A) shows the routing table after a DNS server is added, (B) shows the routing table after a communication destination is added, and (C) shows the routing table after a default gateway is deleted. [Figure 21] Configuration diagram of a network system according to a seventh embodiment [Figure 22] 13A and 13B are diagrams showing routing tables according to a seventh embodiment, in which (A) shows the routing table after a DNS server is added, (B) shows the routing table after a communication destination is added, and (C) shows the routing table after a default gateway is deleted. [Figure 23] 13A and 13B are diagrams showing routing tables according to an eighth embodiment, in which (A) shows the routing table after a DNS server is added, (B) shows the routing table after a communication destination is added, and (C) shows the routing table after a default gateway is deleted. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals.

[0011] (Embodiment 1) 1 is a diagram showing the configuration of a network system 1000 according to this embodiment. The network system 1000 includes a communication device 100, a router 210, a router 220, a terminal device 310, a terminal device 320, a terminal device 330, a terminal device 340, a terminal device 341, a communication network 510, a communication network 520, a communication network 530, and a communication network 540.

[0012] Communication device 100 is a device that communicates with other devices using communication adapter 151 and communication adapter 161. Hereinafter, the other devices will be referred to as communication partners where appropriate. Communication device 100 selects a communication adapter to use for communication by referring to a routing table, which will be described later. Communication device 100 is, for example, a device that manages facilities. As shown in FIG. 2 , communication device 100 includes control unit 11, storage unit 12, display unit 13, operation reception unit 14, first communication unit 15, and second communication unit 16.

[0013] The control unit 11 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), RTC (Real Time Clock), etc. The CPU is also called a central processing unit, central arithmetic unit, processor, microprocessor, microcomputer, DSP (Digital Signal Processor), etc., and functions as a central processing unit that executes processes and calculations related to the control of the communication device 100. In the control unit 11, the CPU reads programs and data stored in the ROM and uses the RAM as a work area to perform overall control of the communication device 100. The RTC is, for example, an integrated circuit with a timekeeping function. The CPU can determine the current date and time from time information read from the RTC.

[0014] The storage unit 12 includes a nonvolatile semiconductor memory such as a flash memory, an EPROM (Erasable Programmable ROM), or an EEPROM (Electrically Erasable Programmable ROM), and serves as a so-called auxiliary storage device. The storage unit 12 stores programs and data used by the control unit 11 to execute various processes. The storage unit 12 also stores data generated or acquired by the control unit 11 executing various processes. The storage unit 12 stores a routing table, which will be described later.

[0015] The display unit 13 displays various images under the control of the control unit 11. For example, the display unit 13 displays a screen for accepting various operations from the user. The display unit 13 includes a touch screen, a liquid crystal display, etc. The operation accepting unit 14 accepts various operations from the user and supplies information indicating the contents of the accepted operations to the control unit 11. The operation accepting unit 14 includes a touch screen, a button, a lever, etc.

[0016] The first communication unit 15 communicates with devices connected to the communication network 510 under the control of the control unit 11. The first communication unit 15 has a function of connecting to the communication network 510, and communicates with the router 210, terminal device 310, etc. connected to the communication network 510. The first communication unit 15 includes a communication adapter 151 that connects to the communication network 510 in accordance with the TCP / IP standard. The communication adapter 151 is a communication interface that complies with standards such as Wi-Fi (registered trademark) and Ethernet (registered trademark).

[0017] The second communication unit 16 communicates with devices connected to the communication network 520 under the control of the control unit 11. The second communication unit 16 has a function of connecting to the communication network 520, and communicates with the router 220, terminal device 320, and the like connected to the communication network 520. The second communication unit 16 includes a communication adapter 161 that connects to the communication network 520 in accordance with the TCP / IP standard. The communication adapter 161 is a communication interface that complies with standards such as Wi-Fi (registered trademark) and Ethernet (registered trademark).

[0018] The router 210 is a communication device that connects the communication network 510 and the communication network 530. The router 210 relays data between the communication network 510 and the communication network 530. The router 210 includes a communication adapter (not shown) that connects to the communication network 510 and a communication adapter (not shown) that connects to the communication network 530. The router 210 functions as a gateway.

[0019] The router 220 is a communication device that connects the communication network 520 and the communication network 540. The router 220 relays data between the communication network 520 and the communication network 540. The router 220 includes a communication adapter (not shown) that connects to the communication network 520, and a communication adapter (not shown) that connects to the communication network 540. The router 220 functions as a gateway.

[0020] The terminal device 310 is a device connected to the communication network 510. The terminal device 310 includes a communication adapter (not shown) that connects to the communication network 510. The terminal device 320 is a device connected to the communication network 520. The terminal device 320 includes a communication adapter (not shown) that connects to the communication network 520.

[0021] Terminal device 330 is a device connected to communication network 530. Terminal device 330 is provided with a communication adapter (not shown) that connects to communication network 530. Terminal device 340 and terminal device 341 are devices connected to communication network 540. Terminal device 340 and terminal device 341 are provided with a communication adapter (not shown) that connects to communication network 540.

[0022] Communication network 510, communication network 520, communication network 530, and communication network 540 are different from one another. Communication network 510, communication network 520, communication network 530, and communication network 540 are, for example, wireless LANs or wired LANs provided within a facility. Communication network 510, communication network 520, communication network 530, and communication network 540 are communication networks that transmit and receive data in accordance with the TCP / IP standard.

[0023] Next, a method for the communication device 100 to identify a communication path using a routing table will be described. A routing table is a table that holds a list of paths to destinations in individual networks. In this embodiment, the routing table includes records that include the destination network ID, subnet mask, gateway IP address, and communication adapter IP address.

[0024] The destination network ID is the ID of the communication network to which you are connecting. The destination network ID is expressed in the same format as an IP address. In the case of IPv (Internet Protocol Version) 4, the IP address may be expressed as a combination of four decimal numbers ranging from 0 to 255, or as a 32-bit binary number separated by 8 bits. Hereinafter, the network ID will be referred to as a subnetwork where appropriate.

[0025] A subnet mask is a numerical value used to distinguish between the network address portion and the host address portion of an IP address, and is used to extract the network address portion from an IP address. The network address portion is the address portion of an IP address that indicates the network. The host address portion is the address portion of an IP address that indicates the terminal. A subnet mask is expressed in decimal, hexadecimal, binary, etc.

[0026] The gateway IP address is the IP address of the gateway used when connecting to the destination communication network. This gateway IP address is the IP address of the communication network on the side of the connection source device as seen from this gateway. The communication adapter IP address is the IP address of the communication adapter used when connecting to the destination communication network.

[0027] An example will be described below in which the IP address of communication device 100 in communication network 510 (hereinafter simply referred to as "IP address of communication device 100") is divided into a network address portion and a host address portion using a subnet mask.

[0028] In this embodiment, the IP address of communication device 100 is "192.168.1.1" in decimal notation and "11000000.10101000.00000001.00000001" in binary notation. Here, it is assumed that the subnet mask is "255.255.255.0" in decimal notation and "11111111.11111111.11111111.00000000" in binary notation.

[0029] Taking the logical product of the binary notation IP address of communication device 100 and the binary notation subnet mask results in "11000000.10101000.00000001.00000000" in binary notation, or "192.168.1.0" in decimal notation. This "192.168.1.0" is the network ID of communication network 510 to which communication device 100 belongs. In this way, in the binary notation subnet mask, the part corresponding to "1" is the network address section, and the part corresponding to "0" is the host address section.

[0030] Here, the number of "1"s in a binary subnet mask is referred to as the subnet mask length. For example, the subnet mask length of a decimal subnet mask of "255.255.255.0" is 24. To express the subnet mask length in an IP address or network ID in IPv4, the subnet mask length is sometimes added to the end of the IP address or network ID. For example, the IP address of the communication device 100 may be written as "192.168.1.1 / 24," and the network ID of the communication network 510 may be written as "192.168.1.0 / 24."

[0031] In this embodiment, the IP address of communication device 100 in communication network 510, i.e., the IP address assigned to communication adapter 151, is "192.168.1.1 / 24." The IP address of communication device 100 in communication network 520, i.e., the IP address assigned to communication adapter 161, is "192.168.2.1 / 24." The IP address of router 210 in communication network 510 is "192.168.1.254 / 24."

[0032] The IP address of the router 210 in the communication network 530 is "192.168.100.254 / 24." The IP address of the router 220 in the communication network 520 is "192.168.2.254 / 24." The IP address of the router 220 in the communication network 540 is "192.168.200.254 / 24."

[0033] The IP address of terminal device 310 is "192.168.1.2 / 24". The IP address of terminal device 320 is "192.168.2.2 / 24". The IP address of terminal device 330 is "192.168.100.1 / 24". The IP address of terminal device 340 is "192.168.200.1 / 24". The IP address of terminal device 341 is "192.168.200.2 / 24".

[0034] The network ID of the communication network 510 is "192.168.1.0 / 24". The network ID of the communication network 520 is "192.168.2.0 / 24". The network ID of the communication network 530 is "192.168.100.0 / 24". The network ID of the communication network 540 is "192.168.200.0 / 24".

[0035] The IP address of each device is assigned by, for example, a Dynamic Host Configuration Protocol (DHCP) server connected to each communication network. For example, the IP address of communication device 100 in communication network 510 is assigned by a DHCP server (not shown) connected to communication network 510. Furthermore, the IP address of communication device 100 in communication network 520 is assigned by a DHCP server (not shown) connected to communication network 520.

[0036] Furthermore, a DHCP server connected to each communication network distributes the IP address of a default gateway to each device. For example, a DHCP server (not shown) connected to communication network 510 distributes the IP address of router 210, which is set as the default gateway, to communication device 100. For example, a DHCP server (not shown) connected to communication network 520 distributes the IP address of router 220, which is set as the default gateway, to communication device 100.

[0037] In this case, the communication device 100 registers both the router 210 and the router 220 as default gateways in the routing table. In this embodiment, the registration of the default gateway is realized by registering a record corresponding to the default gateway. The default gateway is a gateway used when communicating with a communication destination for which an individual route is not registered in the routing table. Note that specifying a default gateway corresponds to specifying a default route, and also corresponds to specifying a communication adapter for connecting to the default gateway. The default route is a route used when communicating with a communication destination for which an individual route is not registered in the routing table.

[0038] The record for setting router 210 as the default gateway (hereinafter referred to as "record A") is a record in which the destination network ID is "0.0.0.0", the subnet mask is "0.0.0.0", the gateway IP address is "192.168.1.254", and the communication adapter IP address is "192.168.1.1". For example, the record for setting router 220 as the default gateway (hereinafter referred to as "record B") is a record in which the destination network ID is "0.0.0.0", the subnet mask is "0.0.0.0", the gateway IP address is "192.168.2.254", and the communication adapter IP address is "192.168.2.1".

[0039] When the communication device 100 and a communication partner are connected to the same communication network, the communication device 100 can communicate with the communication partner in accordance with the TCP / IP standard without referring to a routing table. For example, when the communication device 100 communicates with a terminal device 310 connected to a communication network 510 to which the communication device 100 is connected, the communication device 100 can communicate with the terminal device 310 via a communication adapter 151 for connecting to the communication network 510. Also, when the communication device 100 communicates with a terminal device 320 connected to a communication network 520 to which the communication device 100 is connected, the communication device 100 can communicate with the terminal device 320 via a communication adapter 161 for connecting to the communication network 520.

[0040] On the other hand, if the communication device 100 and the communication partner are not connected to the same communication network, the communication device 100 determines the route to the communication partner by referring to a routing table in accordance with the TCP / IP standard. When the communication device 100 transmits a packet to the communication partner from an appropriate communication adapter, the router 210 or the router 220 that receives this packet appropriately transmits this packet to the communication partner. Therefore, the communication device 100 only needs to appropriately determine the communication adapter to be used for communication with the communication partner. In other words, in this embodiment, determining the route to the communication partner basically means determining the communication adapter to be used for communication with the communication partner.

[0041] If the communication device 100 and the communication partner are not connected to the same communication network, the communication device 100 communicates with the communication partner using a communication adapter having the ID of the communication adapter included in the record with the longest subnet mask length among the records corresponding to the communication networks to which the communication partner is connected. The record corresponding to the communication network to which the communication partner is connected is a record in which the logical product of the IP address of the communication partner and the subnet mask included in the record matches the destination network ID included in the record.

[0042] For example, assume that a record (hereinafter referred to as "record C" as appropriate) with a destination network ID of "192.168.100.0", a subnet mask of "255.255.255.0", a gateway IP address of "192.168.1.254", and a communication adapter IP address of "192.168.1.1" is registered in the routing table, and the communication device 100 communicates with the terminal device 330. In this case, "192.168.100.0", which is the logical product of "192.168.100.1", the IP address of the terminal device 330, and "255.255.255.0", the subnet mask of record C, matches "192.168.100.0", the destination network ID of record C. Therefore, record C is a record corresponding to the communication network to which the communication partner is connected.

[0043] The routing table also has registered therein records A and B corresponding to the default gateway. The logical product "0.0.0.0" of "192.168.100.1", the IP address of the terminal device 330, and "0.0.0.0", the subnet mask of record A, matches "0.0.0.0", the network ID of the destination of record A. Similarly, the logical product "0.0.0.0" of "192.168.100.1", the IP address of the terminal device 330, and "0.0.0.0", the subnet mask of record B, matches "0.0.0.0", the network ID of the destination of record B. Therefore, records A and B are records corresponding to the communication network to which the communication partner is connected.

[0044] Here, the subnet mask length of record A is 0, the subnet mask length of record B is 0, and the subnet mask length of record C is 24. Therefore, the communication device 100 determines the communication adapter 151 having the IP address “192.168.1.1” of the communication adapter included in record C as the communication adapter to be used for communication with the terminal device 330.

[0045] However, it is often difficult for a user to identify the network ID of the communication network to which the communication counterpart is connected and to register a record corresponding to the communication network to which the communication counterpart is connected in the routing table. For example, it is often difficult for a user to identify the network ID of the communication network 530 to which the terminal device 330 is connected. In this case, it is difficult for the user to register record C in the routing table. In this case, the communication device 100 identifies record A and record B as records corresponding to the communication network to which the communication counterpart is connected.

[0046] However, the subnet mask length of record A is 0, and the subnet mask length of record B is 0. Therefore, it is difficult for the communication device 100 to determine whether to adopt record A or record B. In other words, it is difficult for the communication device 100 to determine whether to adopt communication adapter 151 or communication adapter 161 as the communication adapter to use for communication with terminal device 330. If the communication device 100 adopts communication adapter 161 as the communication adapter to use for communication with terminal device 330, it will not be able to communicate with terminal device 330.

[0047] Therefore, in this embodiment, the communication device 100 generates a record to be used for communication with the communication partner from communication destination information that can be easily identified by the user, and registers the generated record in the routing table. In this embodiment, the communication destination information includes the IP address of the communication partner and identification information of the communication adapter used for communication with the communication partner. In other words, it is assumed that even a user who is not familiar with network configurations can easily identify the IP address of the communication partner and the identification information of the communication adapter used for communication with the communication partner.

[0048] The communication device 100 identifies the IP address of the gateway used for communication with the communication partner and the IP address of the communication adapter used for communication with the communication partner from the identification information of the communication adapter used for communication with the communication partner.The communication device 100 then generates a record in which the destination network ID is the IP address of the communication partner, the subnet mask is the full-bit subnet mask "255.255.255.255", the gateway IP address is the IP address of the gateway used for communication with the communication partner, and the communication adapter IP address is the IP address of the communication adapter used for communication with the communication partner.

[0049] For example, in the example described above, the communication device 100 acquires, from the user, communication destination information including "192.168.100.1", which is the IP address of the terminal device 330, which is the communication partner, and identification information of the communication adapter 151 used for communication with the terminal device 330. The communication device 100 identifies "192.168.1.1", which is the IP address of the communication adapter 151, from the identification information of the communication adapter 151. The communication device 100 identifies "192.168.1.254", which is the IP address of the gateway used for communication with the terminal device 330, from the IP address of the communication adapter 151.

[0050] The communication device 100 then generates a record (hereinafter referred to as "record D") in which the destination network ID is "192.168.100.1", the subnet mask is "255.255.255.255", the gateway IP address is "192.168.1.254", and the communication adapter IP address is "192.168.1.1". The communication device 100 registers record D in the routing table.

[0051] At this time, records A, B, and D are registered in the routing table. When the communication device 100 communicates with the terminal device 330, it identifies record D, which has the longest subnet mask length among records A, B, and D, and determines the communication adapter 151 indicated by record D as the communication adapter to be used for communication with the terminal device 330. The destination network ID of record D is set to the IP address of the communication partner, rather than the ID of the communication network to be connected. Therefore, although the method of using a routing table in this embodiment differs from the method of using a general routing table, it is a method that can be used within the scope of TCP / IP implementation.

[0052] When the communication device 100 communicates with a communication partner that is not connected to the communication network 510 or the communication network 520, it is sufficient to register in advance in the routing table a record that corresponds to this communication partner and is similar to record D. However, when there are an unspecified number of communication partners that are not connected to the communication network 510 or the communication network 520, it is not easy to register records that correspond to the unspecified number of communication partners in the routing table. Therefore, for the unspecified number of communication partners, it is preferable to communicate via a default gateway.

[0053] For example, assume that there are a small number of communication partners connected to communication network 530 and an unspecified number of communication partners connected to communication network 540. In this case, it is preferable that communication device 100 registers a record corresponding to the communication partner connected to communication network 530 in the routing table and communicates with the communication partner via the gateway indicated by this record.

[0054] On the other hand, it is preferable for the communication device 100 to communicate with a communication partner connected to the communication network 540 via a default gateway. In this case, of record A indicating the router 210 as the default gateway and record B indicating the router 220 as the default gateway, record A is deleted from the routing table. For example, the communication device 100 can communicate with the terminal device 340 and the terminal device 341 via the router 220 indicated as the default gateway by record B.

[0055] Next, the functions of the communication device 100 will be described with reference to Fig. 3. The communication device 100 functionally comprises a communication destination information acquisition unit 101, a first address identification unit 102, a table management unit 103, a designation information acquisition unit 104, and a communication unit 105. Each of these functions is realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in the ROM or storage unit 12. Then, the CPU executes the programs stored in the ROM or storage unit 12 to realize each of these functions.

[0056] The communication device 100 is connected to a first communication network to which a first gateway is connected and a second communication network to which a second gateway is connected. The router 210 is an example of the first gateway, and the router 220 is an example of the second gateway. The communication network 510 is an example of the first communication network, and the communication network 520 is an example of the second communication network.

[0057] Furthermore, communication device 100 includes a first communication adapter for connecting to a first communication network and a second communication adapter for connecting to a second communication network. Communication adapter 151 is an example of a first communication adapter, and communication adapter 161 is an example of a second communication adapter. Furthermore, storage unit 12 stores a routing table in which records including a destination network ID, a subnet mask, and a gateway IP address are registered. Storage unit 12 is an example of storage means.

[0058] The communication destination information acquisition unit 101 acquires communication destination information from a user. The communication destination information is information for identifying the IP address of the first communication device and the IP address of the first gateway. In this embodiment, the communication destination information includes the IP address of the first communication device and identification information of the first communication adapter. The first communication device is a device connected to the communication device 100 via the first gateway, and is a communication partner of the communication device 100. The terminal device 330 is an example of a first communication device. The communication destination information acquisition unit 101 is an example of a communication destination information acquisition means.

[0059] The first address identification unit 102 identifies the IP address of the first gateway from the identification information of the first communication adapter included in the communication destination information. The identification information of the first communication adapter may be the IP address of the first communication adapter or the name of the first communication adapter. The first address identification unit 102 can identify the IP address of the first communication adapter from the name of the first communication adapter, for example, based on the correspondence information stored in the storage unit 12. The correspondence information is information that associates the IP address of the first communication adapter with the name of the first communication adapter.

[0060] The first address identification unit 102, for example, refers to a routing table to identify the IP address of the first gateway corresponding to the IP address of the first communication adapter. For example, the first address identification unit 102 identifies a record indicating a default gateway from among the records registered in the routing table. The record indicating the default gateway is a record in which the destination network ID and subnet mask are "0.0.0.0".

[0061] The first address identification unit 102 identifies a record in which the IP address of the communication adapter matches the IP address of the first communication adapter from among the records indicating the default gateway. The first address identification unit 102 identifies the IP address of the gateway indicated by the identified record as the IP address of the first gateway. The first address identification unit 102 is an example of a first address identification means.

[0062] The table management unit 103 registers a first record in the routing table. The first record is a record that includes the IP address of the first communication device as the destination network ID, a full-bit subnet mask as the subnet mask, and the IP address of the first gateway or identification information of the first communication adapter as the gateway IP address. The first record is a record for identifying the gateway or communication adapter used when communicating with the first communication device. In this embodiment, the first communication network is a LAN, and it is possible to identify the IP address of the first gateway connected to the first communication network. Therefore, in this embodiment, the first record includes the IP address of the first gateway as the gateway IP address. Record D described above is an example of the first record.

[0063] Table management unit 103 sets the IP address of the first communication device included in the communication destination information acquired by communication destination information acquisition unit 101 as the destination network ID included in the first record. Table management unit 103 also sets a full-bit subnet mask as the subnet mask included in the first record. Table management unit 103 also sets the IP address of the first gateway identified by first address identification unit 102 as the IP address of the gateway included in the first record.

[0064] Furthermore, the table management unit 103 updates the routing table to indicate the second route of the first route and the second route as the default route. The first route is a route that passes through the first communication network. The second route is a route that passes through the second communication network. In other words, when a record corresponding to the communication destination is not registered in the routing table, the table management unit 103 updates the routing table to indicate that communication is to be performed via the second communication network. Communicating via the second communication network corresponds to communicating via the second gateway. In this embodiment, the table management unit 103 updates the routing table to indicate the second gateway as the default gateway.

[0065] For example, after registering the first record in the routing table, the table management unit 103 deletes the second record of the second and third records from the routing table. The second record is a record that indicates the first route as a default route. The third record is a record that indicates the second route as a default route. In this embodiment, the default route is specified by specifying a default gateway. In other words, the second record is a record that indicates the first gateway as the default gateway. Furthermore, the third record is a record that indicates the second gateway connected to the second communication network as the default gateway.

[0066] Note that the above-mentioned record A is an example of a second record, and the above-mentioned record B is an example of a third record. In this way, records corresponding to communication partners that are not connected to the communication network to which the communication device 100 is connected and that cannot communicate via a default gateway are registered in the routing table. On the other hand, the routing table does not register records corresponding to communication partners that are connected to the communication network to which the communication device 100 is connected and records corresponding to communication partners that can communicate via a default gateway. The table management unit 103 is an example of a table management means.

[0067] Here, the contents of the routing table updated by the table management unit 103 will be described with reference to Fig. 4. Fig. 4(A) shows the routing table before a communication destination is added. As shown in Fig. 4(A), the routing table before a communication destination is added includes a second record that indicates the first gateway as the default gateway and a third record that indicates the second gateway as the default gateway. In Fig. 4(A), the record in the first row is the second record, and the record in the second row is the third record.

[0068] Figure 4(B) shows the routing table after the communication destination has been added. As shown in Figure 4(B), the routing table after the communication destination has been added includes a second record that indicates the first gateway as the default gateway, a third record that indicates the second gateway as the default gateway, and a first record that indicates a gateway and a communication adapter for communicating with the first communication device. In Figure 4(B), the record in the first row is the second record, the record in the second row is the third record, and the record in the third row is the first record.

[0069] Figure 4(C) shows the routing table after the default gateway has been deleted. As shown in Figure 4(C), the routing table after the default gateway has been deleted includes a third record that indicates the second gateway as the default gateway, and a first record that indicates the gateway and communication adapter for communicating with the first communication device. In Figure 4(C), the record in the first row is the third record, and the record in the second row is the first record.

[0070] The communication device 100 can determine the communication adapter to use for communication with the communication partner by referencing the routing table after the default gateway has been deleted. For example, when the communication device 100 communicates with the terminal device 330, which is the first communication device, it communicates with the terminal device 330 via the router 210 indicated as the gateway in the first record. Furthermore, when the communication device 100 communicates with the terminal device 340, which is not the first communication device, it communicates with the terminal device 340 via the router 220 indicated as the default gateway in the third record. Similarly, when the communication device 100 communicates with the terminal device 341, which is not the first communication device, it communicates with the terminal device 341 via the router 220 indicated as the default gateway in the third record.

[0071] The specification information acquisition unit 104 acquires specification information from the user. The specification information is information that specifies a default gateway. In this embodiment, the specification information includes, for example, the IP address of the gateway specified as the default gateway. Note that a gateway basically corresponds to a communication adapter for connecting to the gateway. Therefore, the specification information may be information that specifies a communication adapter for connecting to the default gateway. For example, the specification information may include the IP address of a communication adapter for connecting to the default gateway. Note that the table management unit 103 deletes from the routing table records corresponding to gateways that are not specified as the default gateway by the specification information. In this embodiment, the second gateway is specified as the default gateway by the specification information, and a second record corresponding to the first gateway that is not specified as the default gateway by the specification information is deleted from the routing table.

[0072] The communication unit 105 communicates with the first communication device via a first gateway indicated by a first record registered in the routing table. The communication unit 105 also communicates with a second communication device connected to the communication device 100 via a second gateway, which is a default gateway indicated in the routing table. The terminal device 340 and the terminal device 341 are examples of the second communication device.

[0073] In this way, the communication unit 105 communicates with the communication partner by referring to the routing table stored in the storage unit 12. Specifically, the communication unit 105 determines, for each of all records included in the routing table, whether the logical product of the IP address and subnet mask of the communication partner matches the destination network ID. The communication unit 105 identifies the record with the longest subnet mask length from among the records in which the logical product of the IP address and subnet mask of the communication partner matches the destination network ID. The communication unit 105 uses the communication adapter indicated by the identified record to communicate with the communication partner via the gateway indicated by the identified record.

[0074] Next, a description will be given of the table management process executed by the communication device 100 with reference to the flowchart in Fig. 5. The table management process is executed, for example, after the communication device 100 is connected to the communication network 510 and the communication network 520, and a record indicating the router 210 as the default gateway and a record indicating the router 220 as the default gateway are registered in the routing table.

[0075] First, the control unit 11 included in the communication device 100 acquires communication destination information (step S101). For example, the control unit 11 displays a screen for inputting communication destination information on the display unit 13. The user refers to this screen and inputs the IP address of the communication partner and identification information of the communication adapter used for communication with the communication partner. The control unit 11 acquires the communication destination information including the IP address of the communication partner and the identification information of the communication adapter. If there are multiple communication partners, the control unit 11 acquires communication destination information for each of the multiple communication partners.

[0076] When the control unit 11 completes the process of step S101, it executes a record registration process (step S102). The record registration process will be described in detail below with reference to FIG.

[0077] The control unit 11 determines whether the communication partner and the communication device 100 belong to the same communication network (step S201). For example, the control unit 11 determines whether the communication partner is connected to either the communication network 510 or the communication network 520. When the control unit 11 determines that the communication partner and the communication device 100 belong to the same communication network (step S201: YES), the control unit 11 completes the record registration process.

[0078] When the control unit 11 determines that the communication partner and the communication device 100 do not belong to the same communication network (step S201: NO), it identifies the IP address of the communication adapter from the identification information of the communication adapter included in the communication destination information (step S202). For example, the control unit 11 identifies the IP address of the communication adapter from the identification information of the communication adapter based on the correspondence relationship information stored in the storage unit 12. Note that if the identification information of the communication adapter is the IP address of the communication adapter, the processing of step S202 is not necessary.

[0079] When the control unit 11 completes the process of step S202, it identifies the IP address of the gateway from the IP address of the identified communication adapter (step S203). For example, the control unit 11 identifies a record corresponding to the default gateway from among the records registered in the routing table. The control unit 11 identifies a record from among the records corresponding to the default gateway in which the IP address of the communication adapter matches the IP address of the identified communication adapter. The control unit 11 identifies the IP address of the gateway indicated by the identified record.

[0080] When the control unit 11 completes the process of step S203, it registers a record corresponding to the communication partner in the routing table (step S204). This record includes the IP address of the communication partner included in the communication destination information as the destination network ID, a full-bit subnet mask as the subnet mask, the IP address of the gateway identified in step S203 as the gateway IP address, and the IP address of the communication adapter identified in step S202 as the communication adapter IP address. When the control unit 11 completes the process of step S204, it completes the record registration process.

[0081] Upon completing the record registration process of step S102, the control unit 11 acquires the designation information (step S103). For example, the control unit 11 causes the display unit 13 to display a screen for inputting the designation information. The user refers to this screen to input the designation information. That is, the user inputs information on this screen indicating the gateway to be designated as the default gateway or a communication adapter for connecting to the gateway to be designated as the default gateway. Note that, basically, a gateway other than the gateway indicated by the record individually registered in the routing table is designated as the default gateway.

[0082] When the process of step S103 is completed, the control unit 11 deletes the records corresponding to the unspecified default gateways (step S104). That is, the control unit 11 deletes from the routing table the records corresponding to the default gateways other than the default gateway specified by the specification information, among the records corresponding to the default gateways registered in the routing table.

[0083] For example, if the specification information specifies router 220 as the default gateway, of the records specifying router 210 as the default gateway and the records specifying router 220 as the default gateway, the record specifying router 210 as the default gateway is deleted from the routing table. When the control unit 11 completes the processing of step S104, the control unit 11 completes the table management processing.

[0084] In this embodiment, a first record is registered in the routing table, which is a record that includes the IP address of the first communication device as the destination network ID, a full-bit subnet mask as the subnet mask, and the IP address of the first gateway or identification information of the first communication adapter as the gateway IP address, and the routing table is updated to indicate the second route, which is a route via the second communication network, as the default route.

[0085] In this embodiment, when a communication partner is communicable via a first communication network, the communication device 100 communicates with the communication partner via the first communication network in accordance with a first record registered in the routing table. When a communication partner is communicable via a second communication network, the communication device 100 communicates with the communication partner via the second communication network in accordance with a default route indicated in the routing table.

[0086] In other words, in this embodiment, records for communicating with communication partners that cannot communicate via a default gateway are registered in the routing table based on communication destination information that can be easily identified by the user within the scope of TCP / IP implementation. Therefore, according to this embodiment, it is possible to appropriately determine a communication path with a simple configuration without causing the user any trouble.

[0087] In this embodiment, the second record is a record that indicates the first route as a default route, and the third record is a record that indicates the second route as a default route. Therefore, according to this embodiment, the existence of multiple default routes is suppressed, and the communication device 100 is prevented from being unable to communicate with the communication partner.

[0088] In this embodiment, the first communication network and the second communication network are both LANs, and it is possible to easily identify the IP address of the first gateway connected to the first communication network and the IP address of the second gateway connected to the second communication network. Therefore, according to this embodiment, it is not necessary to change the method of using the routing table very much.

[0089] In addition, in this embodiment, a record for communicating with the first communication device is generated based on communication destination information for identifying the IP address of the first communication device and the IP address of the first gateway. Therefore, according to this embodiment, the user's effort in generating a record for communicating with the first communication device is reduced.

[0090] In addition, in this embodiment, a record for communicating with the first communication device is generated based on communication destination information including the IP address of the first communication device and identification information of the first communication adapter. Therefore, according to this embodiment, the user's effort in generating a record for communicating with the first communication device is further reduced.

[0091] (Embodiment 2) In the first embodiment, an example was described in which a user specifies a communication partner by its IP address when adding a record corresponding to the communication partner to a routing table. In the present embodiment, an example is described in which a user specifies a communication partner by its DNS (Domain Name System) host name when adding a record corresponding to the communication partner to a routing table. Note that the description of the same configurations and functions as those in the first embodiment will be omitted or simplified as appropriate.

[0092] Generally, humans find it easier to recognize a device by its DNS hostname, which is expressed as a string of characters, than by its IP address, which is expressed as a string of numbers. Therefore, in this embodiment, a network system is configured so that a device can be recognized by its DNS hostname. A DNS hostname includes a domain name that identifies the network to which the device is connected and a short hostname that identifies the device itself. A DNS hostname that includes a domain name and a short hostname is appropriately referred to as a long hostname. For example, if the short hostname is "test1" and the domain name is "aaa.test2", the long hostname is "test1.aaa.test2".

[0093] When a communication partner is specified by a DNS host name, it is necessary to query a DNS server for the IP address that corresponds to the DNS host name. The process of obtaining the IP address that corresponds to the DNS host name from the DNS server through this query is called name resolution. Basically, a DNS server is provided for each communication network. Therefore, when a communication partner is specified by a DNS host name, it is necessary to query a DNS server provided for the communication network to which the communication partner is connected for the IP address of the communication partner.

[0094] Here, when adding a record corresponding to a communication partner to the routing table, the communication partner is basically connected to the communication device via a gateway that is not set as the default gateway. Therefore, the DNS server that knows the IP address of the communication partner is also basically connected to the communication device via a gateway that is not set as the default gateway. Therefore, before adding a record corresponding to the communication partner to the routing table, the communication device needs to add a record corresponding to the DNS server to the routing table.

[0095] 7 is a diagram showing the configuration of a network system 1200 according to this embodiment. The network system 1200 includes a communication device 120, a router 210, a router 220, a terminal device 310, a terminal device 320, a terminal device 330, a terminal device 340, a terminal device 341, a DNS server 430, a DNS server 440, a communication network 510, a communication network 520, a communication network 530, and a communication network 540. The communication device 120 has a similar physical configuration to the communication device 100.

[0096] The DNS server 430 is a server that provides a mechanism for converting between DNS host names and IP addresses. The DNS server 430 is connected to the communication network 530. Therefore, the DNS server 430 can convert between DNS host names and IP addresses for the terminal device 330 connected to the communication network 530. In other words, the DNS server 430 has a function for converting the DNS host name of the terminal device 330 into the IP address of the terminal device 330, and a function for converting the IP address of the terminal device 330 into the DNS host name of the terminal device 330.

[0097] The DNS server 440 is a server that provides a mechanism for converting between DNS host names and IP addresses. The DNS server 440 is connected to the communication network 540. Therefore, the DNS server 440 can convert between DNS host names and IP addresses for the terminal device 340 and the terminal device 341 connected to the communication network 540.

[0098] Next, the functions of the communication device 120 will be described with reference to Fig. 8. The communication device 120 functionally comprises a communication destination information acquisition unit 101, a first address identification unit 102, a table management unit 103, a designation information acquisition unit 104, a communication unit 105, and a second address identification unit 106. Each of these functions is realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in the ROM or storage unit 12. Then, the CPU executes the programs stored in the ROM or storage unit 12 to realize each of these functions.

[0099] The table management unit 103 adds a fourth record to the routing table. The fourth record is a record used when communicating with the first DNS server. The first DNS server is a device that the communication device 120 uses to perform name resolution for the first communication device and that associates the IP address of the first communication device with the host name of the first communication device. The fourth record is a record that includes the IP address of the first DNS server as the destination network ID, a full-bit subnet mask as the subnet mask, and the IP address of the first gateway as the gateway IP address. Note that the terminal device 330 is an example of the first communication device, the DNS server 430 is an example of the first DNS server, and the router 210 is an example of the first gateway.

[0100] In this embodiment, the communication destination information acquired by the communication destination information acquisition unit 101 includes the DNS host name of the first communication device and identification information of the first communication adapter. Fig. 9 shows a communication destination information registration screen 810 presented by the communication destination information acquisition unit 101 for acquiring the communication destination information.

[0101] Communication destination information registration screen 810 is a screen that accepts the user's input of communication destination information. Communication destination information registration screen 810 includes text boxes 811A, 811B, 811C, drop-down lists 812A, 812B, 812C, and button 813. Text boxes 811A, 811B, and 811C are collectively referred to as text boxes 811, as appropriate. Drop-down lists 812A, 812B, and 812C are collectively referred to as drop-down lists 812, as appropriate.

[0102] The text box 811 and drop-down list 812 are an input interface for receiving communication destination information from the user. One pair of the text box 811 and the drop-down list 812 corresponds to one communication partner. The text box 811 is a text box for inputting the DNS host name of the first communication device. FIG. 9 shows an example in which "Terminal 1" has been input as the DNS host name of the first communication device. When the first communication device is the terminal device 330, "Terminal 1" is the DNS host name of the terminal device 330.

[0103] Drop-down list 812 is a drop-down list for specifying the identification information of a communication adapter to be used for communication with the first communication device. That is, in this embodiment, the user selects the identification information of a communication adapter to be used for communication with the first communication device from among the candidate identification information of communication adapters presented by communication device 120. FIG. 9 shows an example in which "LAN adapter 1" is specified as the identification information of a communication adapter to be used for communication with the first communication device. Note that when the first communication device is terminal device 330, "LAN adapter 1" is the identification information of communication adapter 151. Button 813 is a button that is pressed when input of communication destination information is complete.

[0104] The second address determination unit 106 accesses the first DNS server and determines the IP address of the first communication device from the DNS host name of the first communication device included in the communication destination information. For example, if the first communication device is the terminal device 330, the second address determination unit 106 transmits the DNS host name of the terminal device 330 included in the communication destination information to the DNS server 430. Then, the second address determination unit 106 obtains the IP address of the terminal device 330 from the DNS server 430. The second address determination unit 106 is an example of a second address determination means.

[0105] Table management unit 103 sets the IP address of the first communication device identified by second address identification unit 106 as the destination network ID in the first record. Table management unit 103 also sets a full-bit subnet mask as the subnet mask in the first record. Table management unit 103 also sets the IP address of the first gateway identified by first address identification unit 102 as the gateway IP address in the first record.

[0106] Next, the contents of the routing table updated by the table management unit 103 will be described with reference to Fig. 10. Fig. 10(A) shows the routing table after the DNS server has been added. As shown in Fig. 10(A), the routing table after the DNS server has been added includes a second record that indicates the first gateway as the default gateway, a third record that indicates the second gateway as the default gateway, and a fourth record that indicates a gateway and a communication adapter for communicating with the first DNS server. In Fig. 10(A), the record in the first row is the second record, the record in the second row is the third record, and the record in the third row is the fourth record.

[0107] Figure 10(B) shows the routing table after the communication destination has been added. As shown in Figure 10(B), the routing table after the communication destination has been added includes a second record that indicates the first gateway as the default gateway, a third record that indicates the second gateway as the default gateway, a fourth record that indicates a gateway and a communication adapter for communicating with the first DNS server, and a first record that indicates a gateway and a communication adapter for communicating with the first communication device. In Figure 10(B), the record in the first row is the second record, the record in the second row is the third record, the record in the third row is the fourth record, and the record in the fourth row is the first record.

[0108] Figure 10(C) shows the routing table after the default gateway has been deleted. As shown in Figure 10(C), the routing table after the default gateway has been deleted includes a third record that indicates the second gateway as the default gateway, a fourth record that indicates a gateway and a communication adapter for communicating with the first DNS server, and a first record that indicates a gateway and a communication adapter for communicating with the first communication device. In Figure 10(C), the record in the first row is the third record, the record in the second row is the fourth record, and the record in the third row is the first record.

[0109] The communication device 120 can determine the communication adapter to be used for communication with the first DNS server by referencing the routing table after the DNS server has been added. Therefore, the communication device 120 can access the first DNS server and identify the IP address of the first communication device from the DNS host name of the first communication device. Then, the communication device 120 can generate a routing table after the communication destination has been added.

[0110] Furthermore, the communication device 120 generates a routing table after the default gateway has been deleted by deleting the second record that indicates the first gateway as the default gateway from the routing table after the communication destination has been added. The communication device 120 can determine the communication adapter to be used for communication with the communication partner by referring to the routing table after the default gateway has been deleted.

[0111] Next, the table management process executed by the communication device 120 will be described with reference to the flowchart in Fig. 11. The table management process is executed, for example, after the communication device 120 is connected to the communication network 510 and the communication network 520, and a record indicating the router 210 as the default gateway and a record indicating the router 220 as the default gateway are registered in the routing table.

[0112] First, the control unit 11 acquires communication destination information for communicating with the first DNS server (step S301). That is, the control unit 11 acquires communication destination information that can identify the IP address of the first DNS server and the IP address of a gateway used for communication with the first DNS server. Note that, if an IP address is assigned to each device by a DHCP server (not shown), the communication device 120 can acquire the IP address of the first DNS server and the IP address of the gateway used for communication with the first DNS server from the DHCP server (not shown).

[0113] In this case, for example, the IP address of the first DNS server and the IP address of the gateway used for communication with the first DNS server are stored in the storage unit 12 included in the communication device 120. Therefore, the control unit 11 can acquire communication destination information with the first DNS server as the communication partner from the storage unit 12. In other words, the control unit 11 does not need to acquire communication destination information with the first DNS server as the communication partner from the user.

[0114] If the user manually sets the IP address without using a DHCP server (not shown), the control unit 11 needs to obtain communication destination information for the first DNS server from the user. In this case, for example, an item for setting the IP address of the first DNS server can be added to the screen for setting the IP address of the first communication adapter.

[0115] When the control unit 11 completes the process of step S301, it executes a record registration process (step S302). The record registration process in step S302 is a process of adding a record used for communication with the first DNS server to the routing table, with the first DNS server as the communication partner. This record registration process is basically the same as the record registration process shown in FIG.

[0116] Upon completing the process of step S302, the control unit 11 acquires communication destination information (step S303). For example, the control unit 11 presents a communication destination information registration screen 810 shown in Fig. 9, and acquires communication destination information from the user, including the DNS host name of the communication destination and identification information of the communication adapter used for communication with the communication destination.

[0117] When the process of step S303 is completed, the control unit 11 identifies the IP address of the communication partner from the DNS host name of the communication partner (step S304). For example, the control unit 11 transmits the DNS host name of the communication partner to a first DNS server and obtains the IP address of the communication partner from the first DNS server.

[0118] When the process of step S304 is completed, the control unit 11 executes a record registration process (step S305). This record registration process is basically the same as the record registration process shown in FIG.

[0119] Upon completing the process of step S305, the control unit 11 acquires the designation information (step S306). Upon completing the process of step S306, the control unit 11 deletes the record corresponding to the undesignated default gateway (step S307). Upon completing the process of step S307, the control unit 11 completes the table management process.

[0120] In this embodiment, after the fourth record for communicating with the first DNS server is registered in the routing table, the communication device 120 becomes able to communicate with the first DNS server. Therefore, in this embodiment, when registering the first record for communicating with the first communication device in the routing table, the user can specify the first communication device by the DNS host name of the first communication device rather than the IP address of the first communication device. Therefore, according to this embodiment, it is possible to improve user convenience.

[0121] (Embodiment 3) In the first embodiment, an example in which the communication device 100 is connected to two communication networks has been described. In the present embodiment, an example in which the communication device 130 is connected to three communication networks will be described. Note that the description of the same configurations and functions as those in the first and second embodiments will be omitted or simplified as appropriate.

[0122] 12 is a diagram showing the configuration of a network system 1300 according to this embodiment. The network system 1300 includes a communication device 130, a router 210, a router 220, a router 270, a terminal device 310, a terminal device 320, a terminal device 330, a terminal device 340, a terminal device 341, a terminal device 370, a DNS server 430, a DNS server 440, a DNS server 470, a communication network 510, a communication network 520, a communication network 530, a communication network 540, a communication network 550, a communication network 560, and a communication network 570.

[0123] The communication device 130 physically comprises a control unit 11, a memory unit 12, a display unit 13, an operation reception unit 14, a first communication unit 15, a second communication unit 16, and a third communication unit (not shown).

[0124] The third communication unit (not shown) communicates with devices connected to the communication network 550 under the control of the control unit 11. The third communication unit (not shown) includes a communication adapter 171 that connects to the communication network 550 in accordance with the TCP / IP standard. The communication adapter 171 is a communication interface that complies with standards such as LTE (Long Term Evolution), 4G (4th Generation), and 5G (5th Generation).

[0125] Router 270 is a communication device that connects communication network 560 and communication network 570. Router 270 relays data between communication network 560 and communication network 570. Router 270 includes a communication adapter (not shown) that connects to communication network 560 and a communication adapter (not shown) that connects to communication network 570.

[0126] The terminal device 370 is a device connected to the communication network 570. The terminal device 370 includes a communication adapter (not shown) that connects to the communication network 570.

[0127] The DNS server 470 is a server that provides a mechanism for converting between DNS host names and IP addresses. The DNS server 470 is connected to the communication network 570. Therefore, the DNS server 470 can convert between DNS host names and IP addresses for the terminal devices 370 connected to the communication network 570.

[0128] Communication network 510, communication network 520, communication network 530, communication network 540, communication network 550, communication network 560, and communication network 570 are different from one another. Each of communication network 510, communication network 520, communication network 530, and communication network 540 is, for example, a wireless LAN or a wired LAN provided within a facility.

[0129] The communication network 550 is, for example, a mobile phone network. The communication network 560 is, for example, the Internet. The communication network 570 is, for example, a wireless LAN or a wired LAN provided in another facility. The communication networks 550 and 570 are connected to each other. Note that base stations, exchanges, etc. are not shown in FIG. 12.

[0130] Communication networks 510, 520, 530, 540, 550, 560, and 570 are communication networks that transmit and receive data according to the TCP / IP standard. In this embodiment, communication device 130 can communicate with a communication partner installed in another facility via communication network 550, which is a mobile phone network, and communication network 560, which is the Internet.

[0131] In this embodiment, there are three communication networks connected to communication device 130: communication network 510, communication network 520, and communication network 550. Therefore, in this embodiment, it is preferable that one of the three routes, namely, the route via communication network 510, the route via communication network 520, and the route via communication network 550, is set as the default route, and the other routes are not set as the default route.

[0132] In this embodiment, an example will be described in which a route via communication network 550 is set as the default route. Note that communication device 130 can determine the route to be set as the default route based on the designation information acquired from the user by designation information acquisition unit 104. The designation information includes information indicating the router corresponding to the route to be set as the default route, the communication adapter corresponding to the route to be set as the default route, etc.

[0133] It is preferable that the user sets a route used for communication with an unspecified number of communication partners or a route used for communication with the largest number of communication partners as the default route. For example, when the number of communication partners via communication network 550 is greater than the number of communication partners via communication network 510 and the number of communication partners via communication network 520, it is preferable to set a route via communication network 550 as the default route.

[0134] Communication device 130 is connected to a first communication network, a second communication network, and a third communication network. In this embodiment, each of the first communication network and the third communication network is a LAN, and the second communication network is a mobile phone network. Therefore, in this embodiment, a first gateway connected to the first communication network and a third gateway connected to the third communication network are assumed, but a second gateway connected to the second communication network is not assumed. Communication device 130 includes a first communication adapter for connecting to the first communication network, a second communication adapter for connecting to the second communication network, and a third communication adapter for connecting to the third communication network.

[0135] Communication network 510 is an example of a first communication network. Communication network 520 is an example of a third communication network. Communication network 550 is an example of a second communication network. Communication adapter 151 is an example of a first communication adapter. Communication adapter 161 is an example of a third communication adapter. Communication adapter 171 is an example of a second communication adapter. Router 210 is an example of a first gateway. Router 220 is an example of a third gateway.

[0136] The table management unit 103 registers a first record in the routing table for communicating with a first communication device. The first communication device is a device connected to the communication device 130 via a first gateway. Furthermore, the table management unit 103 registers a fifth record in the routing table for communicating with a third communication device. The third communication device is a device connected to the communication device 130 via a third gateway. Note that the table management unit 103 does not register a record in the routing table for communicating with a second communication device. The terminal device 330 is an example of a first communication device. The terminal devices 340 and 341 are examples of third communication devices. The terminal device 370 is an example of a second communication device.

[0137] The first record is a record that includes the IP address of the first communication device as the destination network ID, a full-bit subnet mask as the subnet mask, and the IP address of the first gateway or identification information of the first communication adapter as the gateway IP address. In this embodiment, the first record includes the IP address of the first gateway as the gateway IP address. The table management unit 103 can generate the first record based on communication destination information related to the first communication device acquired from the user.

[0138] The fifth record is a record that includes the IP address of the third communication device as the destination network ID, a full-bit subnet mask as the subnet mask, and the IP address of the third gateway or identification information of the third communication adapter as the gateway IP address. In this embodiment, the fifth record includes the IP address of the third gateway as the gateway IP address. The table management unit 103 can generate the fifth record based on communication destination information related to the third communication device acquired from the user.

[0139] The table management unit 103 updates the routing table so that the second route of the first, second, and third routes is indicated as the default route. The first route is a route via the first communication network. The second route is a route via the second communication network. The third route is a route via the third communication network.

[0140] For example, after registering the first record and the fifth record in the routing table, the table management unit 103 deletes the second record and the sixth record from the routing table out of the second record, the third record, and the sixth record. The second record is a record that indicates the first route as a default route. The third record is a record that indicates the second route as a default route. The sixth record is a record that indicates the third route as a default route. In this embodiment, the second record is a record that indicates the first gateway as a default gateway. Furthermore, the third record is a record that indicates the second communication adapter as a default gateway. Furthermore, the sixth record is a record that indicates the third gateway as a default gateway.

[0141] In this embodiment, since the first communication network and the third communication network are each a LAN, a first gateway connected to the first communication network and a third gateway connected to the third communication network are assumed. Therefore, for the first communication network and the third communication network, a default gateway and a default route are specified by the gateway. For example, for the first communication network, the IP address of the first gateway is used as the IP address of the gateway. Similarly, for the third communication network, the IP address of the third gateway is used as the IP address of the gateway.

[0142] On the other hand, in this embodiment, since the second communication network is a mobile phone network, a second gateway connected to the second communication network is not assumed. Therefore, for the second communication network, a default gateway and a default route are specified by the communication adapter. For example, for the second communication network, identification information of the second communication adapter is used as the IP address of the gateway. In other words, since a gateway is not assumed for the second communication network, the communication adapter serves as the gateway. For example, in the routing table, identification information of the communication adapter is used for the second communication network instead of the IP address of the gateway.

[0143] The contents of the routing table updated by the table management unit 103 will be described with reference to Fig. 13. Fig. 13(A) shows the routing table before a communication destination is added. As shown in Fig. 13(A), the routing table before a communication destination is added includes a second record that indicates the first gateway as the default gateway, a third record that indicates the second communication adapter as the default gateway, and a sixth record that indicates the third gateway as the default gateway. In Fig. 13(A), the record in the first row is the second record, the record in the second row is the third record, and the record in the third row is the sixth record.

[0144] In this embodiment, the IP address of the gateway and the IP address of the communication adapter are not assumed for the second communication network. Therefore, for the second communication network, the identification information of the communication adapter is used as the IP address of the gateway and the IP address of the communication adapter. In this embodiment, as shown in Figure 13(A), in the third record, the destination network ID and subnet mask are "0.0.0.0", and the IP address of the gateway and the IP address of the communication adapter are "cellular line interface", which is the identification information of the communication adapter 171.

[0145] 13(B) shows the routing table after the communication destination has been added. As shown in FIG. 13(B), the routing table after the communication destination has been added includes a second record indicating the first gateway as the default gateway, a third record indicating the second communication adapter as the default gateway, a sixth record indicating the third gateway as the default gateway, a first record indicating the gateway and communication adapter for communicating with the first communication device, and a fifth record indicating the gateway and communication adapter for communicating with the third communication device. In FIG. 13(B), the record in the first row is the second record, the record in the second row is the third record, the record in the third row is the sixth record, the record in the fourth row is the first record, and the records in the fifth and sixth rows are the fifth record.

[0146] Figure 13(C) shows the routing table after the default gateway has been deleted. As shown in Figure 13(C), the routing table after the default gateway has been deleted includes a third record that indicates the second communication adapter as the default gateway, a first record that indicates the gateway and communication adapter for communicating with the first communication device, and a fifth record that indicates the gateway and communication adapter for communicating with the third communication device. In Figure 13(C), the record in the first row is the third record, the record in the second row is the first record, and the records in the third and fourth rows are the fifth record.

[0147] The communication device 130 can determine the communication adapter to use for communication with the communication partner by referring to the routing table after the default gateway has been deleted. For example, when the communication device 130 communicates with the terminal device 330, which is the first communication device, it communicates with the terminal device 330 via the router 210 indicated as the gateway in the first record. When the communication device 130 communicates with the terminal device 340 or the terminal device 341, which is the third communication device, it communicates with the terminal device 340 or the terminal device 341 via the router 220 indicated as the gateway in the fifth record. When the communication device 130 communicates with the terminal device 370, which is the second communication device, it communicates with the terminal device 370 via the communication adapter 171 indicated as the default gateway in the third record.

[0148] In this embodiment, as in the second embodiment, the user can specify a communication partner by the DNS host name of the communication partner. Therefore, communication device 130 registers a fourth record for communicating with the first DNS server in the routing table before registering a first record for communicating with the first communication device in the routing table. Furthermore, communication device 130 registers a record for communicating with the third DNS server in the routing table before registering a fifth record for communicating with the third communication device in the routing table.

[0149] The third DNS server is a DNS server that associates the IP address of the third communication device with the DNS host name of the third communication device. DNS server 440 is an example of a third DNS server. A record for communicating with the third DNS server is a record that includes the IP address of the third DNS server as the destination network ID, a full-bit subnet mask as the subnet mask, and the IP address of the third gateway as the gateway IP address.

[0150] In this embodiment, when the communication partner is a communication partner that can communicate via a first communication network, communication device 130 communicates with the communication partner via a first gateway indicated by a first record registered in the routing table. When the communication partner is a communication partner that can communicate via a third communication network, communication device 130 communicates with the communication partner via a third gateway indicated by a fifth record registered in the routing table. When the communication partner is a communication partner that can communicate via a second communication network, communication device 130 communicates with the communication partner via a second communication adapter indicated as a default gateway in the routing table.

[0151] That is, in this embodiment, records for communicating with communication partners that cannot communicate via a default gateway are registered in the routing table based on communication destination information that can be easily identified by the user within the scope of TCP / IP implementation. Therefore, according to this embodiment, even if communication device 130 can connect to three communication networks, a communication path can be appropriately determined with a simple configuration without causing the user any trouble.

[0152] In addition, in this embodiment, of the second record which is a record indicating the first route as a default route, the third record which is a record indicating the second route as a default route, and the sixth record which is a record indicating the third route as a default route, the second record and the sixth record are deleted from the routing table. Therefore, according to this embodiment, the existence of multiple default routes is suppressed, and the communication device 130 is prevented from being unable to communicate with the communication partner.

[0153] In this embodiment, the first and third communication networks are LANs, and the second communication network is a mobile phone network. For the second communication network, the second communication adapter is used as a gateway. Therefore, this embodiment does not require significant changes to the way the routing table is used.

[0154] (Fourth embodiment) In the first embodiment, the process of updating the routing table to prevent communication failures due to duplicate registration of multiple default gateways was explained in detail. In this embodiment, the software mechanism for realizing the above process will be explained in detail. Note that the explanation of the same configurations and functions as those in the first to third embodiments will be omitted or simplified as appropriate.

[0155] 14, communication device 140 according to this embodiment includes, as software, an operating system 20, network management software 30, setting modification software 40, and a communication adapter driver 50. Note that communication device 140 has the same hardware configuration as communication device 100.

[0156] The operating system 20 is basic software that manages the entire computer system in the communication device 140. The operating system 20 is software that implements functions for basic management and control of the communication device 140, basic functions that are commonly used by many pieces of software, etc. The operating system 20 manages a routing table 60 in which the network settings of the communication device 140 are registered.

[0157] As described in the first embodiment, the routing table 60 is a table in which records including a destination network ID, a subnet mask, and a gateway IP address are registered. The routing table 60 is stored, for example, in the storage unit 12. When the operating system 20 detects a change in the network settings made by the network management software 30, it notifies the setting modification software 40 of the change in the network settings.

[0158] The network management software 30 is software that manages the network settings of the communication device 140 in cooperation with the operating system 20. The network management software 30 is software that starts up and remains resident immediately after the communication device 140 is started up. The network management software 30 changes the network settings of the communication device 140 by updating the routing table 60. The network settings performed by the network management software 30 include automatic setting by the DHCP server 70 and manual setting by the user 80. Hereinafter, the network settings of the communication device 140 will be referred to simply as network settings where appropriate.

[0159] The setting modification software 40 is application software that works in conjunction with the operating system 20 to modify the network settings of the communication device 140. Application software is software that runs on the operating system 20 and is developed and used for specific functions and purposes. The setting modification software 40 is software that starts up immediately after the communication device 140 is started up and remains resident. The setting modification software 40 can constantly receive various notifications from the operating system 20. The setting modification software 40 modifies the network settings of the communication device 140 by updating the routing table 60.

[0160] If the setting modification software 40 detects that a default gateway has been registered multiple times, it deletes the unnecessary default gateway and registers the necessary communication destination. Specifically, when the setting modification software 40 receives a notification of a change in the network settings from the operating system 20, it determines whether multiple gateways are specified as default gateways in the network settings. If the setting modification software 40 determines that multiple gateways are specified as default gateways, it modifies the network settings so that only the specified gateway among the multiple gateways is specified as the default gateway.

[0161] Furthermore, when modifying the network settings so that only the designated gateway is indicated as the default gateway, the setting modification software 40 modifies the network settings so that the first communication device and the communication device 140 can communicate with each other. The first communication device is a device that is connected to the communication device 140 via a first gateway that is not the designated gateway among multiple gateways. Note that modifying the network settings so that only the designated gateway is indicated as the default gateway corresponds to modifying the network settings so that the designated route, which is a route that passes through the designated gateway, is indicated as the default route.

[0162] When the setting modification software 40 receives a notification of a change in network settings from the operating system 20 and the first route and the second route are indicated as default routes in the routing table 60, the setting modification software 40 registers a first record in the routing table 60 and updates the routing table 60 to indicate the second route as the default route. The second route is the specified route described above. The first route is a route that does not go through the specified gateway but goes through the first gateway. In the example of the first embodiment, the specified gateway is the router 220, the first route is a route that goes through the router 210, and the second route is a route that goes through the router 220.

[0163] The first record is as described in the first embodiment. That is, the first record includes the IP address of the first communication device as the destination network ID. The first record also includes a full-bit subnet mask as the subnet mask. The first record also includes the IP address of the first gateway as the gateway IP address, or identification information of the first communication adapter, which is a communication adapter among multiple communication adapters for connecting the communication device 140 to the first gateway. In the example of the first embodiment, the first communication device is the terminal device 330, and the first communication adapter is the communication adapter 151.

[0164] Furthermore, the setting modification software 40 registers information indicating the first record and information indicating the second route, which is the specified route, as the default route in a recovery file stored in the storage unit 12. The setting modification software 40 executes recovery processing when the network management software 30 deletes the first record from the routing table 60 and updates the routing table 60 to indicate multiple routes including the first route and the second route as the default route. In the recovery processing, the setting modification software 40 registers the first record in the routing table 60 based on the recovery file, and updates the routing table 60 to indicate the second route, which is the specified route, as the default route.

[0165] The communication adapter driver 50 is a device driver for the communication adapters 151 and 161. In other words, the communication adapter driver 50 is software that enables the operating system 20 to control the communication adapters 151 and 161, which are hardware provided in the communication device 140. The communication adapter driver 50 has functions such as sending and receiving packets, notifying link-up, and notifying link-down. Link-up means that the communication device 140 is connected to another device and is in a state where it can communicate with the other device. Link-down means that the communication device 140 is not connected to the other device and is in a state where it cannot communicate with the other device.

[0166] Next, with reference to FIG. 14, a procedure in which the setting modification software 40 modifies the network settings changed by the network management software 30 will be specifically described.

[0167] First, a case where network settings are automatically configured by DHCP will be described. In this case, the network management software 30 functions as a DHCP client and automatically configures the network based on information received from a DHCP server 70. For example, in automatic configuration of the communication network 510, the network management software 30 receives the IP address of the communication device 140 in the communication network 510 from the DHCP server 70 and registers the received IP address of the communication device 140.

[0168] The network management software 30 also registers the router 210, which is the default gateway designated by the DHCP server 70, in the routing table 60. Here, the network management software 30 registers the new default gateway in the routing table 60 even if another default gateway has already been registered in the routing table 60. The other default gateway is, for example, the router 220 in the communication network 520.

[0169] Note that the network settings are updated via the operating system 20. That is, the network management software 30 and the setting modification software 40 can update the network settings using commands prepared by the operating system 20. The commands include a command to register an IP address of a communication adapter, a command to delete an IP address of a communication adapter, a command to add a default gateway, a command to delete a default gateway, a command to add a communication destination, a command to delete a communication destination, a command to obtain a registered default gateway, and the like.

[0170] Furthermore, when the network settings are updated, the operating system 20 notifies the setting modification software 40 that the network settings have been updated. Note that updating the routing table 60 corresponds to updating the network settings. Therefore, when the routing table 60 is updated, the operating system 20 notifies the setting modification software 40 that the routing table 60 has been updated. For example, when the network management software 30 updates the routing table 60, the operating system 20 notifies the setting modification software 40 that the routing table 60 has been updated.

[0171] The content of the notification by the operating system 20 can be adjusted as appropriate. For example, the content of the notification may be that the routing table 60 has been updated, that a default gateway has been added to the routing table 60, or the IP address of the default gateway that has been added to the routing table 60.

[0172] When the setting modification software 40 receives a notification from the operating system 20 that a default gateway has been added to the routing table 60, it checks whether or not there are any duplicate default gateways registered. For example, the setting modification software 40 identifies the default gateways registered in the routing table 60 using a command to obtain the default gateways registered in the routing table 60. When the setting modification software 40 determines that multiple default gateways are registered in the routing table 60, it executes the table management process described in the first embodiment.

[0173] In the table management process, the setting modification software 40 acquires from the user specification information that specifies a default gateway and communication destination information that indicates communication destinations that can be communicated with via unspecified default gateways. In the table management process, the setting modification software 40 deletes the unspecified default gateways and adds communication destinations that can be communicated with via the unspecified default gateways.

[0174] That is, the setting modification software 40 uses a command to delete a default gateway to delete an unspecified default gateway from the routing table 60. The setting modification software 40 also uses a command to add a communication destination to add a communication destination to the routing table 60 that can be communicated with via an unspecified default gateway.

[0175] Next, a case where the network settings are manually configured by the user 80 will be described. The user 80 is, for example, a network administrator. In this case, the network management software 30 performs network configuration based on information acquired from the user 80. For example, the network management software 30 updates the contents of a configuration file based on the information acquired from the user 80, and updates the routing table 60 according to the contents of the configuration file. The configuration file is a file that holds network settings, and is stored in the storage unit 12, for example.

[0176] Here, for example, if a configuration file is provided for each communication adapter, a default route is specified for each configuration file. In this case, the network management software 30 registers multiple default gateways in the routing table 60. The operating system 20 notifies the configuration modification software 40 that a default gateway has been added to the routing table 60. When the configuration modification software 40 receives notification from the operating system 20 that a default gateway has been added to the routing table 60, it checks whether or not a duplicate default gateway has been registered. If the configuration modification software 40 determines that multiple default gateways are registered in the routing table 60, it executes the table management processing described in the first embodiment.

[0177] In this way, in either the automatic setting or manual setting case, if a duplicate default gateway is registered in the routing table 60, the routing table 60 is appropriately corrected. Specifically, the unspecified default gateway is deleted from the routing table 60, and a communication destination that can be communicated via the unspecified default gateway is registered in the routing table 60. As a result, the occurrence of communication failures is suppressed.

[0178] Next, a case where the network settings are reset due to a link-down and a link-up will be described. The case where a link-down and a link-up occurs in the communication adapter 151 connected to the router 210 that is not designated as the default gateway will be described.

[0179] First, when a communication cable (not shown) is disconnected from the communication adapter 151, the communication adapter driver 50 notifies the operating system 20 of a link down. In this case, the operating system 20 notifies the network management software 30 of the link down. Upon receiving the link down notification from the operating system 20, the network management software 30 deletes information about the linked down communication adapter 151 from the network settings. For example, the network management software 30 uses a command to delete an IP address to delete the IP address of the communication adapter 151.

[0180] Furthermore, the network management software 30 uses a command to delete a communication destination to delete the communication destination that can be communicated with via the communication adapter 151 from the routing table 60. This deletion of the communication destination corresponds to the deletion of the first record. The operating system 20 may notify the setting modification software 40 that the communication destination has been deleted from the routing table 60. However, at this point, there is no duplicate registration of the default gateway. Therefore, even if the setting modification software 40 receives this notification from the operating system 20, it does not modify the routing table 60.

[0181] Here, for example, when a communication cable (not shown) is plugged into the communication adapter 151, the communication adapter driver 50 notifies the operating system 20 of link-up. In this case, the operating system 20 notifies the network management software 30 of link-up. When the network management software 30 receives the link-up notification from the operating system 20, it adds information about the linked-up communication adapter 151 to the network settings.

[0182] For example, if automatic configuration using DHCP is employed, the network management software 30 acquires various information from the DHCP server 70 and updates the routing table 60 based on the acquired information. Specifically, for example, the network management software 30 uses a command to register an IP address to add the IP address of the communication adapter 151. The network management software 30 also uses a command to add a default gateway to add the router 210 connected to the communication adapter 151 to the routing table 60 as a default gateway.

[0183] Furthermore, for example, when manual configuration is employed, the network management software 30 acquires information written in a configuration file stored in the storage unit 12 and updates the network configuration based on the acquired information. Specifically, for example, the network management software 30 uses a command to register an IP address to register the IP address of the communication adapter 151. Furthermore, the network management software 30 uses a command to add a default gateway to add the router 210 connected to the communication adapter 151 to the routing table 60 as a default gateway.

[0184] When a default gateway is registered in the routing table 60, the operating system 20 notifies the setting modification software 40 that a default gateway has been registered in the routing table 60. When the setting modification software 40 receives notification of the registration of a default gateway from the operating system 20, it determines whether or not there is a duplicate registration of the default gateway. If the setting modification software 40 determines that there is a duplicate registration of the default gateway, it deletes the unspecified default gateway from the routing table 60 and adds to the routing table 60 communication destinations that can be communicated via the unspecified default gateway.

[0185] Here, if there is no difference between the network configuration before link-down and the network configuration after link-up, the setting modification software 40 can update the routing table 60 using the recovery file. The network configuration may be the configuration of a communication adapter provided in the communication device 140. In other words, if the communication adapter provided in the communication device 140 before link-down matches the communication adapter provided in the communication device 140 after link-up, the setting modification software 40 may determine that there is no difference between the network configuration before link-down and the network configuration after link-up.

[0186] When executing table management processing before a link-down occurs, the setting modification software 40 can write the network configuration, specification information, and communication destination information to a recovery file. That is, the recovery file records, for example, the network configuration before the link-down, the specification information before the link-down, and the communication destination information before the link-down. The setting modification software 40 can recover the contents of the routing table 60 based on the information written in the recovery file.

[0187] Specifically, the setting modification software 40 deletes from the routing table 60 any default gateways other than the default gateway specified by the specification information written in the recovery file. The setting modification software 40 also adds the communication destination indicated by the communication destination information written in the recovery file to the routing table 60. According to this operation, when a link down and a link up occur, the contents of the routing table 60 are automatically restored, thereby suppressing the occurrence of communication failures.

[0188] Next, the setting modification process executed by the communication device 140 will be described with reference to the flowchart in Fig. 15. The setting modification process is implemented as setting modification software 40. The setting modification process is executed in response to, for example, a notification from the operating system 20 to the setting modification software 40 of a change in network settings.

[0189] First, the control unit 11 acquires network settings (step S401). For example, the control unit 11 uses a command to acquire a registered default gateway to identify a default gateway registered in the routing table 60. After completing the processing of step S401, the control unit 11 determines whether or not multiple default gateways exist (step S402). In other words, the control unit 11 determines whether or not multiple default gateways are registered in the routing table 60.

[0190] If the control unit 11 determines that there are not multiple default gateways (step S402: NO), it completes the setting correction process. On the other hand, if the control unit 11 determines that there are multiple default gateways (step S402: YES), it determines whether automatic recovery is possible (step S403). For example, the control unit 11 may determine that automatic recovery is possible if a recovery file is stored in the storage unit 12. Alternatively, for example, the control unit 11 may determine that automatic recovery is possible if there is no difference between the current network configuration and the network configuration recorded in the recovery file.

[0191] If the control unit 11 determines that automatic recovery is possible (step S403: YES), it reads information from the recovery file (step S404). Specifically, the control unit 11 reads the specification information and communication destination information from the recovery file. On the other hand, if the control unit 11 determines that automatic recovery is not possible (step S403: NO), it acquires the specification information from the user 80 (step S405). In other words, the control unit 11 accepts the specification of the default gateway from the user 80.

[0192] Upon completing the process of step S405, the control unit 11 acquires communication destination information from the user 80 (step S406). That is, the control unit 11 receives from the user 80 a designation of a communication destination with which communication is possible via a gateway that is not designated as the default gateway. Upon completing the process of step S406, the control unit 11 writes the designation information and communication destination information to a recovery file (step S407).

[0193] When the control unit 11 completes the process of step S404 or step S407, it deletes the default gateway (step S408). Specifically, the control unit 11 uses a command to delete the default gateway to delete the default gateway that is not specified by the specification information from the routing table 60.

[0194] Upon completing the process of step S408, the control unit 11 adds the communication destination (step S409). Specifically, the control unit 11 uses a command to add a communication destination to add the communication destination indicated by the communication destination information to the routing table 60. Upon completing the process of step S409, the control unit 11 completes the setting correction process.

[0195] When multiple default gateways are registered in the routing table 60, it is difficult for the communication device 140 to identify a communication adapter for communicating with a communication partner. If the communication device 140 selects an incorrect communication adapter, the communication device 140 will be unable to communicate with the communication partner, resulting in a communication failure. As a technique related to this problem, the above-mentioned Patent Document 1 describes a technique for determining a communication path using a dummy address and determining a communication adapter to be used for communication.

[0196] However, the technology described in Patent Document 1 is a technology that deviates significantly from TCP / IP implementation and requires complicated processing. Therefore, there is a demand for a technology that can prevent the continuation of a state in which multiple default gateways are registered in duplicate, that is, a technology that can prevent the occurrence of communication failures with a simple configuration. According to this embodiment, it is possible to prevent the occurrence of communication failures with a simple configuration.

[0197] Specifically, in this embodiment, when multiple gateways are specified as default gateways in the network settings, the network settings are corrected so that only a specified gateway among the multiple gateways is specified as the default gateway. This embodiment prevents multiple default gateways from being registered in duplicate and continuing. Therefore, this embodiment makes it possible to prevent communication failures with a simple configuration.

[0198] Furthermore, in this embodiment, a method is adopted in which the setting modification software 40 quickly resolves the duplicate registration of multiple default gateways when the duplicate registration of multiple default gateways is made by the network management software 30. Here, a method can be considered in which the operating system 20 or the network management software 30 is modified to prevent the duplicate registration of multiple default gateways.

[0199] However, modifying the operating system 20 affects various processes, so modifying the operating system 20 is not easy. Furthermore, the network management software 30 is closely linked to the operating system 20. Furthermore, modifying the network management software 30 corresponds to modifying the DHCP implementation. Therefore, modifying the network management software 30 is also not easy. In other words, software development is easy with the method of preparing setting modification software 40 without making any changes to the operating system 20 and network management software 30, as in this embodiment.

[0200] In this embodiment, when the setting correction software 40 receives a notification of a change in network settings from the operating system 20, it quickly detects and resolves the duplicate registration of multiple default gateways. Therefore, according to this embodiment, the period during which multiple default gateways are duplicately registered is extremely short, and the possibility of a communication failure occurring is considered extremely low.

[0201] Furthermore, in this embodiment, when the duplicate registration of multiple default gateways is resolved, the network settings are corrected so that the first communication device connected via a gateway that is not designated as the default gateway can communicate with the communication device 140. Specifically, when the routing table 60 is updated to indicate a designated route that passes through the designated gateway as the default route, a first record for enabling communication between the first communication device and the communication device 140 is registered in the routing table 60. Therefore, according to this embodiment, it is possible to realize communication using multiple communication adapters while suppressing the occurrence of communication failures.

[0202] Furthermore, in this embodiment, the contents of the routing table 60 are automatically restored based on the recovery file. Specifically, in this embodiment, when a first record is deleted from the routing table 60 and the routing table 60 is updated to indicate multiple routes as default routes, the first record is registered in the routing table 60 based on the recovery file, and the routing table 60 is updated to indicate the specified route as the default route. Therefore, according to this embodiment, it is possible to prevent communication failures from occurring without causing any trouble to the user.

[0203] (Embodiment 5) In the second embodiment, an example was described in which a route between two LANs and a mobile phone network, and one that passes through the mobile phone network, is set as the default route. In the present embodiment, an example is described in which a route between a LAN and a mobile phone network, and one that passes through the LAN, is set as the default route. Note that the description of the same configurations and functions as those in the first to fourth embodiments will be omitted or simplified as appropriate.

[0204] Whether to set the default route as a route via a LAN or a route via a mobile phone network can be adjusted as appropriate. For example, it is preferable to set the default route depending on the difficulty of obtaining the IP address of the communication partner. Specifically, for example, if it is difficult to obtain the IP address of a communication partner connected to a communication device via a mobile phone network, it is preferable to set the default route as a route via a mobile phone network. Conversely, for example, if it is difficult to obtain the IP address of a communication partner connected to a communication device via a LAN, it is preferable to set the default route as a route via a LAN.

[0205] In this embodiment, an example will be described in which a route via the LAN is set as a default route when it is difficult to obtain the IP address of a communication partner connected to a communication device via a LAN. An example in which it is difficult to obtain the IP address of a communication partner connected to a communication device via a LAN is when the communication partner is connected to the LAN by a VPN (Virtual Private Network).

[0206] 16 is a diagram showing the configuration of a network system 1500 according to this embodiment. The network system 1500 includes a communication device 150, a router 210, a terminal device 310, a terminal device 330, a server 711A, a server 711B, a server 711C, a DNS server 712, a communication network 510, a communication network 530, a communication network 550, and a communication network 560.

[0207] Server 711A, server 711B, and server 711C are a group of distribution servers that store the same content in a CDN (Content Delivery Network). A CDN is a network optimized for distributing web content over the Internet. A CDN is equipped with multiple distribution servers that store the same content. A CDN is a system in which servers are made redundant to reduce server load, protect against DOS attacks (Denial of Service attacks), and so on.

[0208] In this embodiment, it is assumed that the CDN 710 includes a server 711A, a server 711B, a server 711C, and a DNS server 712. Of course, the CDN 710 may include four or more servers 711. The servers 711A, 711B, and 711C are origin servers that store original content, or cache servers that store copies of the original content. The same DNS host name is assigned to the servers 711A, 711B, and 711C. The communication device 150 acquires content from any of the servers 711A, 711B, and 711C. The server 711 is a collective term for the servers 711A, 711B, and 711C. The server 711 includes a communication adapter (not shown) that connects to the communication network 560.

[0209] The DNS server 712 is a server that provides a mechanism for converting DNS host names and IP addresses. The DNS server 712 performs name resolution for servers within the CDN 710. That is, the DNS server 712 performs name resolution for servers 711A, 711B, and 711C. For example, when the DNS server 712 receives the DNS host name of server 711, it transmits the IP address of server 711 that provides the content from among servers 711A, 711B, and 711C. That is, when the DNS server 712 receives the DNS host name of server 711, it transmits one of the IP addresses of server 711A, server 711B, and server 711C.

[0210] The method for determining the server 711 that provides the content can be adjusted as appropriate. For example, the DNS server 712 determines the server 711 that provides the content based on the communication device that made the name resolution request, the time of the name resolution request, etc. The DNS server 712 includes a communication adapter (not shown) that connects to the communication network 560.

[0211] Each of the communication networks 510 and 530 is, for example, a wireless LAN or a wired LAN provided within a facility. The communication network 550 is, for example, a mobile phone network. The communication network 560 is, for example, the Internet. Note that base stations, exchanges, etc. are not shown in FIG. 16. The communication networks 510, 530, 550, and 560 are communication networks that transmit and receive data in accordance with the TCP / IP standard.

[0212] In this embodiment, a route via communication network 510 is set as the default route. In other words, communication network 510 is an example of a second communication network. Communication network 550 is an example of a first communication network. Communication adapter 151 is an example of a second communication adapter. Communication adapter 171 is an example of a first communication adapter.

[0213] Next, the functions of communication device 150 will be described with reference to Fig. 17. Communication device 150 functionally includes communication destination information acquisition unit 101, table management unit 103, designation information acquisition unit 104, communication unit 105, and second address identification unit 106.

[0214] The communication destination information acquisition unit 101 acquires communication destination information from a user. In this embodiment, the communication destination information includes a DNS host name of the first communication device and identification information of the first communication adapter. In this embodiment, the first communication device is a server 711.

[0215] The table management unit 103 manages the routing table 60. The table management unit 103 also manages a name resolution file 62. The name resolution file 62 is a file for resolving the name of the first communication device without accessing a DNS server. In other words, the name resolution file 62 is a file for identifying the IP address of the first communication device from the DNS host name of the first communication device. The name resolution file 62 includes name resolution information in which the DNS host name of the first communication device is associated with the IP address of the first communication device. The name resolution file 62 is, for example, a hosts file. The hosts file is a database of DNS host names in a computer that uses TCP / IP, and is a text file in which the correspondence between IP addresses and DNS host names is described.

[0216] In this embodiment, the contents of the routing table 60 and the contents of the name resolution file 62 are synchronized. That is, when the table management unit 103 writes a first record including the IP address of the first communication device to the routing table 60, the table management unit 103 writes name resolution information in which the DNS host name of the first communication device is associated with the IP address of the first communication device to the name resolution file 62. In this case, it is ensured that the IP address of the first communication device included in the name resolution information in the name resolution file 62 is included in the first record of the routing table 60. With this configuration, the communication device 150 can communicate with the first communication device by using the IP address of the first communication device acquired by referring to the name resolution file 62.

[0217] Note that a user, software, or the like generally specifies a first communication device using a DNS hostname rather than an IP address. Therefore, the communication device 150 needs to access a first DNS server that associates the IP address of the first communication device with the hostname of the first communication device. Therefore, the communication device 150 needs to register a record corresponding to the first DNS server in the routing table 60.

[0218] Therefore, the table management unit 103 adds a fourth record for communicating with the first DNS server to the routing table 60. The fourth record is a record that includes the IP address of the first DNS server as the destination network ID, a full-bit subnet mask as the subnet mask, and identification information of the first communication adapter as the gateway IP address. The DNS server 712 is an example of the first DNS server. The communication adapter 171 is an example of the first communication adapter.

[0219] The designation information acquisition unit 104 acquires designation information from the user. In this embodiment, the designation information includes the IP address of the router 210 designated as the default gateway. The second address identification unit 106 accesses the first DNS server and identifies the IP address of the first communication device from the DNS host name of the first communication device included in the communication destination information.

[0220] The table management unit 103 registers a first record in the routing table 60, the first record including the IP address of the first communication device identified by the second address identification unit 106 as the destination network ID and the identification information of the first communication adapter as the gateway IP address. The table management unit 103 also deletes from the routing table 60 the second record that indicates the first communication adapter as the default gateway.

[0221] 18, the reason why the communication device 150 is able to communicate with the first communication device by synchronizing the contents of the routing table 60 with the contents of the name resolution file 62 will be described. As shown in FIG. 18, the communication device 150 includes network management software 30, general software 41, management software 42, a DNS cache 61, and a name resolution file 62.

[0222] The network management software 30 is software that manages the network settings of the communication device 150 in cooperation with the operating system 20. The general software 41 is application software other than the management software 42 among the application software.

[0223] The management software 42 is application software for managing the routing table 60 and the name resolution file 62. The communication destination information acquisition unit 101, the table management unit 103, the specified information acquisition unit 104, the communication unit 105, the second address identification unit 106, etc. may be implemented as the management software 42.

[0224] The DNS cache 61 temporarily stores the results of name resolution by the DNS server 712. In other words, the DNS cache 61 temporarily stores name resolution information obtained by the network management software 30 accessing the DNS server 712.

[0225] The general software 41 basically performs name resolution via the network management software 30. That is, the general software 41 supplies a DNS host name to the network management software 30 and obtains an IP address corresponding to this DNS host name from the network management software 30. Meanwhile, the network management software 30 obtains the IP address corresponding to the DNS host name in the following order of priority: name resolution file 62, DNS cache 61, and DNS server 712.

[0226] That is, the network management software 30 first determines whether or not the name resolution information including the supplied DNS host name is registered in the name resolution file 62. If the name resolution information including the supplied DNS host name is registered in the name resolution file 62, the network management software 30 supplies the IP address included in this name resolution information to the general software 41. If the name resolution information including the supplied DNS host name is not registered in the name resolution file 62, the network management software 30 determines whether or not the name resolution information including the supplied DNS host name is stored in the DNS cache 61.

[0227] If name resolution information including the supplied DNS host name is stored in the DNS cache 61, the network management software 30 supplies the IP address included in this name resolution information to the general software 41. If name resolution information including the supplied DNS host name is not stored in the DNS cache 61, the network management software 30 accesses the DNS server 712 to obtain an IP address corresponding to this DNS host name and supplies the obtained IP address to the general software 41. The network management software 30 also stores in the DNS cache 61 name resolution information in which this DNS host name is associated with the obtained IP address.

[0228] On the other hand, the management software 42 basically performs name resolution without going through the network management software 30. That is, the management software 42 accesses the DNS server 712 to obtain an IP address corresponding to a DNS host name. For example, the management software 42 provides the DNS host name of the first communication device to the DNS server 712 and obtains the IP address of the first communication device from the DNS server 712. The management software 42 registers a first record including the obtained IP address of the first communication device in the routing table 60.

[0229] Here, if the IP address of the first communication device acquired from the DNS server 712 changes, a mismatch may occur between the IP address of the first communication device included in the first record of the routing table 60 and the IP address of the first communication device acquired by the general software 41. For example, the management software 42 may acquire the IP address of the server 711A from the DNS server 712 when registering the first record, and the general software 41 may acquire the IP address of the server 711B from the DNS server 712 or the DNS cache 61 via the network management software 30 when accessing the first communication device.

[0230] In this case, the general software 41 attempts to access the server 711B using the IP address of the server 711B. However, since the first record including the IP address of the server 711B is not registered in the routing table 60, the general software 41 cannot access the server 711B.

[0231] Therefore, in this embodiment, the name resolution file 62 is updated so that the IP address of the first communication device acquired by the general software 41 matches the IP address of the first communication device included in the first record registered in the routing table 60. In other words, the management software 42 updates the name resolution file 62 when registering the first record.

[0232] Specifically, the management software 42 accesses the DNS server 712 and acquires the IP address of the first communication device that corresponds to the DNS host name of the first communication device. The management software 42 registers a first record including the acquired IP address of the first communication device in the routing table 60. The management software 42 also registers name resolution information in the name resolution file 62, in which the acquired IP address of the first communication device and the host name of the first communication device are associated with each other.

[0233] In this case, when the general software 41 provides the host name of the first communication device to the network management software 30, the network management software 30 refers to the name resolution file 62. Here, the name resolution file 62 registers name resolution information in which the host name of the first communication device is associated with the IP address of the first communication device. Therefore, the network management software 30 obtains the IP address of the first communication device that is associated with the host name of the first communication device in the name resolution information, and provides it to the general software 41. It is guaranteed that the IP address of the first communication device provided to the general software 41 is included in the first record registered in the routing table 60. Therefore, the general software 41 can access the first communication device using the obtained IP address of the first communication device.

[0234] It should be noted that the IP address of the first communication device acquired from the DNS server 712 may become invalid. For example, if server 711A is excluded from the servers 711, the IP address of server 711A previously acquired from the DNS server 712 becomes invalid. Therefore, it is preferable that the routing table 60 and the name resolution file 62 be updated periodically. For example, it is preferable that the management software 42 periodically executes the following processes: accessing the DNS server 712 to acquire the IP address of the first communication device; updating the routing table 60 so that the first record includes the acquired IP address; and updating the name resolution file 62 so that the name resolution information includes the acquired IP address.

[0235] Next, the contents of the routing table 60 updated by the table management unit 103 will be described with reference to Fig. 19. Fig. 19(A) shows the routing table 60 after the DNS server has been added. As shown in Fig. 19(A), the routing table 60 after the DNS server has been added includes a third record indicating router 210, which is the second gateway, as the default gateway, a second record indicating communication adapter 171, which is the first communication adapter, as the default gateway, and a fourth record for communicating with DNS server 712, which is the first DNS server. In Fig. 19, the cellular line interface corresponds to communication adapter 171. In Fig. 19(A), the record in the first row is the third record, the record in the second row is the second record, and the record in the third row is the fourth record.

[0236] 19(B) shows the routing table 60 after the communication destination has been added. As shown in FIG. 19(B), the routing table 60 after the communication destination has been added is a table in which a first record for communicating with server 711B, which is the first communication device, has been added to the routing table 60 after the DNS server has been added.

[0237] Figure 19(C) shows the routing table 60 after the default gateway has been deleted. As shown in Figure 19(C), the routing table 60 after the default gateway has been deleted is a table in which the second record indicating the first communication adapter, communication adapter 171, as the default gateway has been deleted from the routing table 60 after the communication destination has been added.

[0238] The communication device 150 can refer to the fourth record to communicate with the DNS server 712, which is the first DNS server. Also, the communication device 150 can refer to the first record to communicate with the server 711B, which is the first communication device.

[0239] In this embodiment, the route via the LAN out of the LAN and the mobile phone network is set as the default route. Therefore, according to this embodiment, for example, when it is difficult to obtain the IP address of a communication partner connected via the LAN, communication with both the communication partner connected via the LAN and the communication partner connected via the mobile phone network is possible.

[0240] In this embodiment, a fourth record that enables access to the first DNS server is registered in the routing table 60. Therefore, according to this embodiment, by accessing the first DNS server, it is possible to identify the IP address of the first communication device from the DNS host name of the first communication device.

[0241] In this embodiment, name resolution information in which the DNS host name of the first communication device is associated with the IP address of the first communication device is registered in a name resolution file 62 that is referenced during name resolution by application software. Therefore, according to this embodiment, access to the first communication device by application software is possible.

[0242] (Sixth embodiment) In the fifth embodiment, a method for enabling access to the first communication device using the name resolution file 62 was described. In the present embodiment, a method for enabling access to the first communication device without using the name resolution file 62 will be described. Note that the description of the same configurations and functions as those in the first to fifth embodiments will be omitted or simplified as appropriate.

[0243] In this embodiment, it is assumed that when the first DNS server receives the DNS host name of the first communication device, it transmits multiple IP addresses as the IP address of the first communication device. In other words, when the DNS server 712 receives the DNS host name of server 711, it transmits the IP address of server 711A, the IP address of server 711B, and the IP address of server 711C.

[0244] The second address identification unit 106 identifies the multiple IP addresses received from the first DNS server as the IP addresses of the first communication device. That is, the second address identification unit 106 identifies all of the IP addresses of the servers 711A, 711B, and 711C as the IP addresses of the server 711.

[0245] The table management unit 103 registers in the routing table 60 a first record corresponding to each of the multiple IP addresses identified by the second address identification unit 106. That is, the table management unit 103 registers in the routing table 60 a first record including the IP address of the server 711A, a first record including the IP address of the server 711B, and a first record including the IP address of the server 711C.

[0246] Next, the contents of the routing table 60 updated by the table management unit 103 will be described with reference to Fig. 20. Fig. 20(A) shows the routing table 60 after the DNS server has been added. The routing table 60 after the DNS server has been added shown in Fig. 20(A) is the same as the routing table 60 after the DNS server has been added shown in Fig. 19(A).

[0247] Figure 20(B) shows the routing table 60 after the communication destination has been added. As shown in Figure 20(B), the routing table 60 after the communication destination has been added is a table in which a first record for communicating with server 711A, which is the first communication device, a first record for communicating with server 711B, which is the first communication device, and a first record for communicating with server 711C, which is the first communication device, have been added to the routing table 60 after the DNS server has been added.

[0248] Figure 20(C) shows the routing table 60 after the default gateway has been deleted. As shown in Figure 20(C), the routing table 60 after the default gateway has been deleted is a table in which the second record indicating the first communication adapter, communication adapter 171, as the default gateway has been deleted from the routing table 60 after the communication destination has been added.

[0249] In this embodiment, a first record corresponding to each of all IP addresses corresponding to the IP address of server 711 is registered in routing table 60. Therefore, when general software 41 accesses server 711, no matter which of server 711A, server 711B, or server 711C the IP address of server 711 obtained from network management software 30 is, general software 41 can access server 711 using the obtained IP address of server 711.

[0250] If there is a possibility that the IP address of the first communication device obtained from the DNS server 712 may become invalid, it is preferable to periodically update the routing table 60. For example, it is preferable that the management software 42 periodically executes a process of accessing the DNS server 712 to obtain multiple IP addresses of the first communication device, and a process of updating the routing table 60 so that it includes multiple first records corresponding to each IP address.

[0251] In this embodiment, a first record corresponding to each of the multiple IP addresses acquired from the DNS server 712 is registered in the routing table 60. Therefore, according to this embodiment, it is possible to enable application software to access the first communication device without updating the name resolution file 62.

[0252] (Embodiment 7) In the fifth embodiment, an example has been described in which the first communication device is a redundant server 711 in a CDN 710. In the present embodiment, an example will be described in which the first communication device is a redundant NTP server 721 in an NTP (Network Time Protocol) system 720. Note that the description of the same configurations and functions as those in the first to sixth embodiments will be omitted or simplified as appropriate.

[0253] 21 is a diagram showing the configuration of a network system 1700 according to this embodiment. The network system 1700 includes a communication device 170, a router 210, a terminal device 310, a terminal device 330, an NTP server 721A, an NTP server 721B, an NTP server 721C, a DNS server 722, a communication network 510, a communication network 530, a communication network 550, and a communication network 560.

[0254] NTP server 721A, NTP server 721B, and NTP server 721C are a group of servers that provide the same time information in the NTP system 720. The NTP system 720 is a system for adjusting and synchronizing the time information of devices connected to a network. In other words, the NTP system 720 is a system that provides the same time information using a plurality of redundant servers. In this embodiment, it is assumed that the NTP system 720 includes NTP server 721A, NTP server 721B, and NTP server 721C. It goes without saying that the NTP system 720 may include four or more NTP servers 721. NTP server 721 is a collective term for NTP server 721A, NTP server 721B, and NTP server 721C.

[0255] The NTP server 721A, NTP server 721B, and NTP server 721C are assigned the same DSN host name. The communication device 170, which is an NTP client, acquires time information from any one of the NTP server 721A, NTP server 721B, and NTP server 721C. The NTP server 721 includes a communication adapter (not shown) that connects to the communication network 560.

[0256] The DNS server 722 is a server that provides a mechanism for converting DNS host names and IP addresses. The DNS server 722 performs name resolution for the servers in the NTP system 720. That is, the DNS server 722 performs name resolution for the NTP server 721A, the NTP server 721B, and the NTP server 721C.

[0257] For example, when the DNS server 722 receives the DNS host name of the NTP server 721, it transmits the IP addresses of all the NTP servers 721, that is, the IP addresses of the NTP servers 721A, 721B, and 721C. Meanwhile, the communication device 170, which is the NTP client, selects one IP address from all the received IP addresses and acquires time information from the NTP server 721 having the selected IP address. The DNS server 722 includes a communication adapter (not shown) that connects to the communication network 560.

[0258] Here, either "server" or "pool" can be set for the NTP client. If "server" is set for the NTP client, when the NTP client accesses the NTP server 721, the NTP client executes name resolution using the network management software 30 to obtain the IP address of the NTP server 721, and accesses the NTP server 721 using the obtained IP address. Therefore, if "server" is set for the NTP client, the name resolution file 62 is referenced when accessing the NTP server 721.

[0259] On the other hand, when "pool" is set for the NTP client, the NTP client acquires all IP addresses of the NTP server 721 at startup and stores them in the storage unit 12. When accessing the NTP server 721, the NTP client selects one IP address from all the stored IP addresses in accordance with a predetermined procedure and accesses the NTP server 721 using the selected IP address. Therefore, when "pool" is set for the NTP client, the name resolution file 62 is not referenced when accessing the NTP server 721.

[0260] In this embodiment, a method will be described in which the name resolution file 62 is used to enable access to the NTP server 721 when "server" is set as the NTP client.

[0261] First, when the first DNS server receives the DNS host name of the first communication device, it transmits multiple IP addresses as the IP address of the first communication device. That is, when the DNS server 722 receives the host name of the NTP server 721 from the communication device 170, it transmits the IP addresses of the NTP servers 721A, 721B, and 721C to the communication device 170 as the IP addresses of the NTP server 721. The NTP server 721 is an example of a first communication device. The DNS server 722 is an example of a first DNS server.

[0262] The second address determination unit 106 determines one of the multiple IP addresses received from the first DNS server as the IP address of the first communication device. For example, the second address determination unit 106 determines one of the IP addresses of the NTP server 721A, the IP address of the NTP server 721B, and the IP address of the NTP server 721C as the IP address of the NTP server 721.

[0263] The table management unit 103 registers a first record including the IP address of the first communication device identified by the second address identification unit 106 in the routing table 60. The table management unit 103 also registers, in the name resolution file 62, name resolution information in which the DNS host name of the first communication device and the IP address of the first communication device identified by the second address identification unit 106 are associated with each other.

[0264] In this way, the management software 42, which functions as the table management unit 103, the second address identification unit 106, etc., synchronizes the contents registered in the routing table 60 with the contents registered in the name resolution file 62. For example, the management software 42 accesses the DNS server 722 and acquires multiple IP addresses of the first communication device corresponding to the DNS host name of the first communication device. The management software 42 registers a first record including the IP address of one first communication device selected from the acquired multiple IP addresses in the routing table 60. The management software 42 also registers name resolution information in the name resolution file 62, in which the IP address of the selected one first communication device is associated with the host name of the first communication device.

[0265] In this case, when the general software 41, which implements an NTP client, supplies the host name of the first communication device to the network management software 30, the network management software 30 refers to the name resolution file 62. Here, the name resolution file 62 registers name resolution information in which the host name of the first communication device is associated with the IP address of the first communication device. Therefore, the network management software 30 acquires the IP address of the first communication device, which is associated with the host name of the first communication device in the name resolution information, and supplies it to the general software 41. It is guaranteed that the IP address of the first communication device supplied to the general software 41 is included in the first record registered in the routing table 60. Therefore, the general software 41 can access the first communication device using the acquired IP address of the first communication device.

[0266] Note that using only a specific server among the NTP servers 721 is undesirable from the perspective of load balancing. Therefore, it is preferable that the routing table 60 and the name resolution file 62 are updated periodically so that the NTP server 721 to be used can be switched periodically. For example, the management software 42 stores multiple IP addresses obtained from the DNS server 722 in the storage unit 12 and periodically switches the IP address to be used. In other words, it is preferable that the management software 42 periodically executes a process of updating the routing table 60 so that the IP address included in the first record is switched, and a process of updating the name resolution file 62 so that the IP address included in the name resolution information is switched.

[0267] It should be noted that the IP address of the first communication device acquired from the DNS server 722 may become invalid. For example, if the NTP server 721A is excluded from the NTP server 721, the IP address of the NTP server 721A previously acquired from the DNS server 722 becomes invalid. Therefore, it is preferable that the management software 42 periodically executes a process of accessing the DNS server 722 and acquiring multiple IP addresses of the first communication device.

[0268] Next, the contents of the routing table 60 updated by the table management unit 103 will be described with reference to Fig. 22. Fig. 22(A) shows the routing table 60 after the DNS server has been added. The routing table 60 after the DNS server has been added shown in Fig. 22(A) is the same as the routing table 60 after the DNS server has been added shown in Fig. 19(A).

[0269] Figure 22(B) shows the routing table 60 after the communication destination has been added. As shown in Figure 22(B), the routing table 60 after the communication destination has been added is a table in which a first record for communicating with the NTP server 721A, which is the first communication device, has been added to the routing table 60 after the DNS server has been added.

[0270] Figure 22(C) shows the routing table 60 after the default gateway has been deleted. As shown in Figure 22(C), the routing table 60 after the default gateway has been deleted is a table in which the second record indicating the first communication adapter, communication adapter 171, as the default gateway has been deleted from the routing table 60 after the communication destination has been added.

[0271] The communication device 170 can refer to the fourth record to communicate with the DNS server 722, which is the first DNS server. Also, the communication device 170 can refer to the first record to communicate with the NTP server 721A, which is the first communication device.

[0272] In this embodiment, one of the multiple IP addresses acquired from the DNS server 722 is identified as the IP address of the first communication device. Then, a first record including the identified IP address is registered in the routing table 60, and name resolution information including the identified IP address is registered in the name resolution file 62. Therefore, according to this embodiment, it is possible for application software to access the first communication device.

[0273] (Embodiment 8) In the seventh embodiment, a method for enabling access to the first communication device using the name resolution file 62 was described. In the present embodiment, a method for enabling access to the first communication device without using the name resolution file 62 will be described. Note that the description of the same configurations and functions as those in the first to seventh embodiments will be omitted or simplified as appropriate.

[0274] In this embodiment, a method for enabling access to the NTP server 721 without using the name resolution file 62 when a "pool" is set in the NTP client will be described.

[0275] First, when the first DNS server receives the DNS host name of the first communication device, it transmits a plurality of IP addresses as the IP address of the first communication device. The second address determination unit 106 determines the plurality of IP addresses received from the first DNS server as the IP address of the first communication device. The table management unit 103 registers in the routing table 60 first records including each of the plurality of IP addresses determined by the second address determination unit 106.

[0276] In this way, the management software 42 functioning as the table management unit 103, the second address identification unit 106, etc. accesses the first DNS server and acquires multiple IP addresses of the first communication device corresponding to the DNS host name of the first communication device. The management software 42 registers multiple first records, each including the acquired multiple IP addresses, in the routing table 60.

[0277] In this case, the general software 41, which has an NTP client implemented, selects one IP address from the multiple IP addresses of the first communication device stored in itself according to a predetermined procedure, and attempts to access the first communication device using the selected IP address. It is guaranteed that all of the multiple IP addresses of the first communication device stored in the general software 41 are included in the first record registered in the routing table 60. Therefore, the general software 41 can access the first communication device using the selected IP address of the first communication device.

[0278] Next, the contents of the routing table 60 updated by the table management unit 103 will be described with reference to Fig. 23. Fig. 23(A) shows the routing table 60 after the DNS server has been added. The routing table 60 after the DNS server has been added shown in Fig. 23(A) is the same as the routing table 60 after the DNS server has been added shown in Fig. 22(A).

[0279] Figure 23(B) shows the routing table 60 after the communication destination has been added. As shown in Figure 23(B), the routing table 60 after the communication destination has been added is a table in which a first record for communicating with the NTP server 721A, which is the first communication device, a first record for communicating with the NTP server 721B, which is the first communication device, and a first record for communicating with the NTP server 721C, which is the first communication device, have been added to the routing table 60 after the DNS server has been added.

[0280] Figure 23(C) shows the routing table 60 after the default gateway has been deleted. As shown in Figure 23(C), the routing table 60 after the default gateway has been deleted is a table in which the second record indicating the first communication adapter, communication adapter 171, as the default gateway has been deleted from the routing table 60 after the communication destination has been added.

[0281] The communication device 170 can refer to the fourth record to communicate with the DNS server 722, which is the first DNS server. Also, the communication device 170 can refer to the three first records to communicate with the three NTP servers 721, which are first communication devices.

[0282] In this embodiment, first records corresponding to each of the multiple IP addresses acquired from the DNS server 722 are registered in the routing table 60. Therefore, according to this embodiment, it is possible to enable application software to access the first communication device without updating the name resolution file 62.

[0283] (Variation) Although the embodiments of the present disclosure have been described above, various modifications and applications are possible when implementing the present disclosure. It is optional which parts of the configurations, functions, and operations described in the above embodiments are adopted in the present disclosure. Furthermore, in addition to the above-described configurations, functions, and operations, further configurations, functions, and operations may also be adopted in the present disclosure. Furthermore, the configurations, functions, and operations described in the above-described embodiments can be freely combined.

[0284] The number and types of communication networks connected to a communication device are not limited to those shown in embodiments 1-3. For example, four or more communication networks may be connected to a communication device. Also, one LAN and one mobile phone network may be connected to a communication device. Also, three LANs may be connected to a communication device. Below, Modification 1 and Modification 2 are shown as typical modifications.

[0285] (Variation 1) The network system according to the first modification includes a first communication network which is a LAN and a second communication network which is a mobile phone network. The first communication network is, for example, the communication network 510 in the third embodiment. The second communication network is, for example, the communication network 550 in the third embodiment. In other words, the network system according to the first modification is basically a network system in which the communication network 520 is excluded from the network system according to the third embodiment. In the first modification, the second route which is a route via the second communication network is set as the default route.

[0286] In the first modification, the first record is a record that includes the IP address of the first communication device as the destination network ID, a full-bit subnet mask as the subnet mask, and the IP address of the first gateway as the gateway IP address. The first communication device is, for example, the terminal device 330 in the third embodiment. The first gateway is, for example, the router 210 in the third embodiment. The second record is a record that indicates the first gateway as the default gateway. Furthermore, the third record is a record that indicates the second communication adapter as the default gateway. The second communication adapter is, for example, the communication adapter 171 in the third embodiment.

[0287] In the first modification, when a communication device communicates with a first communication device, the communication device communicates with the first communication device via a first communication network in accordance with a first record registered in the routing table. Also, in the first modification, when the communication device communicates with a second communication device connected to the communication device via a second communication network, the communication device communicates with the second communication device via the second communication network in accordance with a default route indicated in the routing table. The second communication device is, for example, the terminal device 370 in the third embodiment.

[0288] (Variation 2) The network system according to the second modification includes a first communication network which is a mobile phone network and a second communication network which is a LAN. The first communication network is, for example, the communication network 550 in the third embodiment. The second communication network is, for example, the communication network 510 in the third embodiment. In other words, the network system according to the first modification is basically a network system in which the communication network 520 is excluded from the network system according to the third embodiment. In the second modification, the second route which is a route via the second communication network is set as the default route.

[0289] In the second modification, the first record is a record that includes the IP address of the first communication device as the destination network ID, a full-bit subnet mask as the subnet mask, and identification information of the first communication adapter as the gateway IP address. The first communication device is, for example, the terminal device 370 in the third embodiment. The first communication adapter is, for example, the communication adapter 171 in the third embodiment. The second record is a record that indicates the first communication adapter as the default gateway. Furthermore, the third record is a record that indicates the second gateway connected to the second communication network as the default gateway. The second gateway is, for example, the router 210 in the third embodiment.

[0290] In the second modification, when a communication device communicates with a first communication device, the communication device communicates with the first communication device via a first communication network in accordance with a first record registered in the routing table. Also, in the first modification, when a communication device communicates with a second communication device connected to the communication device via a second communication network, the communication device communicates with the second communication device via the second communication network in accordance with a default route indicated in the routing table. The second communication device is, for example, the terminal device 330 in the third embodiment.

[0291] (Other variations) In the first to third embodiments, a method was described in which, among multiple records indicating default gateways, all records except for one record indicating a single specified default gateway are deleted. Other methods may be used to indicate a single default gateway in a routing table. For example, a metric value may be included in the records registered in the routing table, and the metric value of the record indicating the specified default gateway may be set to the minimum value. In this case, among the records indicating default gateways, records with metric values ​​other than the minimum value are not actually used.

[0292] Furthermore, the record indicating the default route may be any record that can identify the communication adapter to be used when a record corresponding to the communication destination is not registered in the routing table. For example, in the third embodiment, if the identifier of the second communication adapter and the identifier of the second communication network are associated with each other, the third record may be the identifier of the second communication network instead of the identifier of the second communication adapter. This is because, even in such a configuration, the communication adapter to be used when a record corresponding to the communication destination is not registered in the routing table can be identified from the identifier of the second communication network indicated by the third record.

[0293] In the first to third embodiments, examples have been described in which a default gateway is specified by specification information. The default gateway may also be determined automatically. For example, a gateway not indicated by a record corresponding to a communication partner registered in the routing table may be set as the default gateway. For example, in the third embodiment, if the first record corresponding to the first communication device indicates the first gateway and the fifth record corresponding to the third communication device indicates the third gateway, the second communication adapter may be set as the default gateway.

[0294] In the third embodiment, an example has been described in which communication adapter 171 is set as the default gateway. Router 210 or router 220 may also be set as the default gateway. It is preferable that a router or communication adapter used for communication with an unspecified number of communication partners is set as the default gateway. For example, a router or communication adapter used for communication with communication partners whose IP addresses are difficult to identify may be set as the default gateway. Alternatively, a router or communication adapter used for communication with the most communication partners may be set as the default gateway.

[0295] In the seventh embodiment, an example has been described in which, when "server" is set as the NTP client, one IP address is selected from the acquired plurality of IP addresses, and the routing table 60 and the name resolution file 62 are updated so as to enable communication with the first communication device having the selected IP address. When "server" is set as the NTP client, similar to the eighth embodiment, the routing table 60 may be updated so as to enable communication with all first communication devices without using the name resolution file 62.

[0296] In the seventh and eighth embodiments, an example was described in which the NTP client is a resident NTP client. The NTP client may also be a one-shot startup NTP client. Even in this case, it is possible to adopt the method of synchronizing the contents of the routing table 60 with the contents of the name resolution file 62 as shown in the seventh embodiment, or the method of updating the routing table 60 so that it includes first records corresponding to all of the acquired IP addresses as shown in the eighth embodiment.

[0297] The present disclosure allows various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. Furthermore, the above-described embodiments are intended to illustrate the present disclosure and do not limit the scope of the present disclosure. That is, the scope of the present disclosure is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of equivalent disclosures are considered to be within the scope of the present disclosure.

[0298] This application is based on International Application No. PCT / JP2023 / 001219 filed on January 17, 2023, and International Application No. PCT / JP2023 / 021348 filed on June 8, 2023. The entire specifications, claims, and drawings of International Application No. PCT / JP2023 / 001219 and International Application No. PCT / JP2023 / 021348 are incorporated herein by reference. [Industrial Applicability]

[0299] The present disclosure is applicable to a network system including multiple communication networks. [Explanation of symbols]

[0300] 11 control unit, 12 memory unit, 13 display unit, 14 operation reception unit, 15 first communication unit, 16 second communication unit, 20 operating system, 30 network management software, 40 setting correction software, 41 general software, 42 management software, 50 communication adapter driver, 60 routing table, 61 DNS cache, 62 name resolution file, 70 DHCP server, 80 user, 100, 120, 130, 140, 150, 170 communication device, 101 communication destination information acquisition unit, 102 first address identification unit, 103 table management unit, 104 specified information acquisition unit, 105 communication unit, 106 second address identification unit, 151, 161, 171 communication adapter, 210, 220, 270 router, 310, 320, 330, 340, 341, 370 Terminal device, 430, 440, 470, 712, 722 DNS server, 510, 520, 530, 540, 550, 560, 570 Communication network, 710 CDN, 711, 711A, 711B, 711C Server, 720 NTP system, 721, 721A, 721B, 721C NTP server, 810 Communication destination information registration screen, 811, 811A, 811B, 811C Text box, 812, 812A, 812B, 812C Drop-down list, 813 Button, 1000, 1200, 1300, 1500, 1700 Network system

Claims

1. A communication device connected to a first communication network and a second communication network, a first communications adapter for connecting to the first communications network; a second communication adapter for connecting to the second communication network; a storage means for storing a routing table in which a record including a destination network ID, a subnet mask, and an IP address of a gateway is registered; a table management means for registering in the routing table a first record which is a record including, as the destination network ID, an IP address of a first communication device connected to the communication device via the first communication network and another communication network connected to the first communication network, a full-bit subnet mask as the subnet mask, and, as the gateway IP address, an IP address of a first gateway connected to the first communication network or identification information of the first communication adapter, and updating the routing table so as to indicate, as a default route, a second route out of a first route which is a route via the first communication network and a second route which is a route via the second communication network, Communication equipment.

2. the table management means registers the first record in the routing table, and deletes the second record from the routing table, of a second record that is a record indicating the first route as the default route and a third record that is a record indicating the second route as the default route. The communication device according to claim 1 .

3. each of the first communication network and the second communication network is a LAN; the first record is a record including an IP address of the first gateway as an IP address of the gateway, the second record is a record indicating the first gateway as a default gateway, the third record is a record indicating a second gateway connected to the second communication network as the default gateway; The communication device according to claim 2 .

4. the first communication network is a LAN, the second communication network is a mobile phone network; the first record is a record including an IP address of the first gateway as an IP address of the gateway, the second record is a record indicating the first gateway as a default gateway, the third record is a record indicating the second communication adapter as the default gateway; The communication device according to claim 2 .

5. a communication destination information acquiring means for acquiring, from a user, communication destination information for identifying an IP address of the first communication device and an IP address of the first gateway; the table management means registers the first record in the routing table, the first record including an IP address of the first communication device identified from the communication destination information as the destination network ID, and an IP address of the first gateway identified from the communication destination information as the gateway IP address; A communication device according to any one of claims 1 to 4.

6. the communication destination information includes an IP address of the first communication device and identification information of the first communication adapter; a first address specifying means for specifying an IP address of the first gateway from identification information of the first communication adapter included in the communication destination information; the table management means registers the first record in the routing table, the first record including the IP address of the first communication device included in the communication destination information as the destination network ID, and the IP address of the first gateway identified by the first address identification means as the gateway IP address; The communication device according to claim 5 .

7. the table management means registers in the routing table a fourth record which is a record including, as the destination network ID, an IP address of a first DNS server which associates the IP address of the first communication device with a DNS host name of the first communication device, which includes, as the subnet mask, the full-bit subnet mask, and which includes, as the gateway IP address, an IP address of the first gateway; the communication destination information includes a DNS host name of the first communication device and identification information of the first communication adapter; a second address specifying means for accessing the first DNS server and specifying an IP address of the first communication device from a DNS host name of the first communication device included in the communication destination information; the table management means registers the first record in the routing table, the first record including, as the destination network ID, the IP address of the first communication device identified by the second address identification means, and the first record including, as the gateway IP address, the IP address of the first gateway identified from the identification information of the first communication adapter included in the communication destination information; The communication device according to claim 5 .

8. connected to the first communication network, the second communication network, and a third communication network; a third communication adapter for connecting to the third communication network; the table management means registers in the routing table a fifth record which is a record including, as the destination network ID, an IP address of a third communication device connected to the communication device via the third communication network and another communication network connected to the third communication network, the full-bit subnet mask as the subnet mask, and, as the gateway IP address, an IP address of a third gateway connected to the third communication network or identification information of the third communication adapter, and updates the routing table so as to indicate, as the default route, the second route among the first route, the second route, and a third route which is a route via the third communication network. A communication device according to any one of claims 1 to 4.

9. the table management means registers the first record and the fifth record in the routing table, and deletes the second record and the sixth record from the routing table, among a second record which is a record indicating the first route as the default route, a third record which is a record indicating the second route as the default route, and a sixth record which is a record indicating the third route as the default route. The communication device according to claim 8.

10. each of the first communication network and the third communication network is a LAN; the second communication network is a mobile phone network; the first record is a record including an IP address of the first gateway as an IP address of the gateway, the second record is a record indicating the first gateway as a default gateway, the third record is a record indicating the second communication adapter as the default gateway, the fifth record is a record including an IP address of the third gateway as an IP address of the gateway, the sixth record is a record indicating the third gateway as the default gateway. The communication device according to claim 9.

11. the first communication network is a mobile phone network; the second communication network is a LAN; the first record is a record including identification information of the first communication adapter as an IP address of the gateway, the second record is a record indicating the first communication adapter as a default gateway, the third record is a record indicating a second gateway connected to the second communication network as the default gateway; The communication device according to claim 2 .

12. the table management means registers in the routing table a fourth record which is a record including, as the destination network ID, an IP address of a first DNS server which associates the IP address of the first communication device with a DNS host name of the first communication device, which includes the full-bit subnet mask as the subnet mask, and which includes identification information of the first communication adapter as the IP address of the gateway; a second address specifying means for accessing the first DNS server and specifying an IP address of the first communication device from the DNS host name of the first communication device; the table management means registers the first record in the routing table, the first record including the IP address of the first communication device identified by the second address identification means as the destination network ID and the identification information of the first communication adapter as the gateway IP address; The communication device according to claim 11.

13. when the first DNS server receives the DNS host name of the first communication device, it transmits any one IP address of a plurality of IP addresses as the IP address of the first communication device; the second address identification means identifies the IP address received from the first DNS server as the IP address of the first communication device; the table management means registers name resolution information in which the DNS host name of the first communication device and the IP address of the first communication device identified by the second address identification means are associated with each other in a name resolution file that is referenced when application software obtains the IP address of the first communication device from the DNS host name of the first communication device; The communication device of claim 12.

14. when the first DNS server receives the DNS host name of the first communication device, it transmits a plurality of IP addresses as the IP address of the first communication device; the second address specifying means specifies one of the plurality of IP addresses received from the first DNS server as the IP address of the first communication device; the table management means registers name resolution information in which the DNS host name of the first communication device and the IP address of the first communication device identified by the second address identification means are associated with each other in a name resolution file that is referenced when application software obtains the IP address of the first communication device from the DNS host name of the first communication device; The communication device of claim 12.

15. when the first DNS server receives the DNS host name of the first communication device, it transmits a plurality of IP addresses as the IP address of the first communication device; the second address identification means identifies the plurality of IP addresses received from the first DNS server as IP addresses of the first communication device; the table management means registers the first records corresponding to the plurality of IP addresses identified by the second address identification means in the routing table; The communication device of claim 12.

16. network management software that updates the routing table to change the network settings of the communication device; an operating system that detects and notifies changes to the network configuration by the network management software; setting modification software, which is application software that updates the routing table and modifies the network settings, and which functions as the table management means; when the setting correction software receives a notification of a change in the network setting from the operating system and, if the first route and the second route are indicated as the default route in the routing table, registers the first record in the routing table and updates the routing table to indicate the second route as the default route; A communication device according to any one of claims 1 to 4.

17. the setting correction software registers information indicating the first record and information indicating the second route as the default route in a recovery file stored in the storage means; When the network management software deletes the first record from the routing table and updates the routing table to indicate the first route and the second route as the default route, the setting correction software registers the first record in the routing table based on the recovery file and updates the routing table to indicate the second route as the default route.

17. The communication device of claim 16.

18. A communication device connected to a plurality of communication networks via a plurality of communication adapters, network management software for modifying the network settings of the communication device; an operating system that detects and notifies changes to the network configuration by the network management software; setting modification software, which is application software for modifying the network settings; When the setting modification software receives a notification of a change in the network settings from the operating system and, if a plurality of gateways are indicated as default gateways in the network settings, it acquires, from a user, designation information that designates a gateway among the plurality of gateways to be set as the default gateway, and modifies the network settings so that only the gateway among the plurality of gateways designated by the designation information is indicated as the default gateway. Communication equipment.

19. When the setting modification software modifies the network settings so that only the designated gateway is indicated as the default gateway, the software modifies the network settings so that the communication device can communicate with a first communication device that is connected to the communication device via a first gateway that is not the designated gateway among the plurality of gateways.

20. The communication device of claim 18.

20. a storage means for storing a routing table in which a record including a destination network ID, a subnet mask, and an IP address of a gateway is registered; the setting correction software registers in the routing table a first record which is a record including the IP address of the first communication device as the destination network ID, a full-bit subnet mask as the subnet mask, and the IP address of the first gateway as the gateway IP address or identification information of a first communication adapter which is a communication adapter for connecting the communication device to the first gateway among the plurality of communication adapters, and updates the routing table to indicate a designated route which is a route via the designated gateway as a default route; 20. The communication device of claim 19.

21. the setting correction software registers information indicating the first record and information indicating the specified route as the default route in a recovery file stored in the storage means; When the network management software deletes the first record from the routing table and updates the routing table to indicate multiple routes as the default route, the setting correction software registers the first record in the routing table based on the recovery file and updates the routing table to indicate the specified route as the default route.

21. The communication device of claim 20.

22. A network system comprising: a first communication network; a second communication network; a communication device connected to the first communication network and the second communication network; and a first gateway connected to the first communication network, The communication device a first communications adapter for connecting to the first communications network; a second communication adapter for connecting to the second communication network; a storage means for storing a routing table in which a record including a destination network ID, a subnet mask, and an IP address of a gateway is registered; a table management means for registering in the routing table a first record which is a record including, as the destination network ID, an IP address of a first communication device connected to the communication device via the first communication network and another communication network connected to the first communication network, a full-bit subnet mask as the subnet mask, and an IP address of the first gateway or identification information of the first communication adapter as the gateway IP address, and updating the routing table so that the second route, out of a first route which is a route via the first communication network and a second route which is a route via the second communication network, is indicated as a default route. Network system.

23. A communication method executed by a communication device connected to a first communication network and a second communication network, comprising: connecting to the first communications network via a first communications adapter; connecting to the second communications network via a second communications adapter; storing a routing table in which a record including a destination network ID, a subnet mask, and an IP address of a gateway is registered; registering in the routing table a first record which is a record including, as the destination network ID, an IP address of a first communication device connected to the communication device via the first communication network and another communication network connected to the first communication network, a full-bit subnet mask as the subnet mask, and, as the gateway IP address, an IP address of a first gateway connected to the first communication network or identification information of the first communication adapter; updating the routing table so as to indicate, as a default route, a second route that is a route via the second communication network and a first route that is a route via the first communication network; communicating with the first communication device via the first communication network in accordance with the first record registered in the routing table; communicating with a second communication device connected to the communication device via the second communication network according to the default route indicated by the routing table; Communication method.

24. a computer provided in a communication device including a first communication adapter for connecting to a first communication network, a second communication adapter for connecting to a second communication network, and storage means for storing a routing table in which a record including a destination network ID, a subnet mask, and a gateway IP address is registered; registering a first record in the routing table, the first record being a record including, as the destination network ID, an IP address of a first communication device connected to the communication device via the first communication network and another communication network connected to the first communication network, a full-bit subnet mask as the subnet mask, and, as the gateway IP address, an IP address of a first gateway connected to the first communication network or identification information of the first communication adapter; and causing the device to function as table management means that updates the routing table so as to indicate, as a default route, a second route out of a first route that is a route via the first communication network and a second route that is a route via the second communication network; program.

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