Network system and packet relay method

Abstract

The problem is to enable a terminal device, which is connected to a closed network and has limited access to devices in an external network, to access an external device under certain conditions. [Solution] A network system 10 includes a repeater 20, terminal devices 30a, 30b, and 30c, and a broadband router 40. When the terminal device 30a connects to an HTTP server on an external network N, the terminal device 30a transmits a packet to a relay IP address set in the repeater 20. The repeater 20 converts the source IP address and destination IP address of the received packet into a predetermined IP address and transmits the packet to an HTTP server 50, thereby enabling even the terminal device 30a connected to a closed network in which no DNS server is installed to connect to the HTTP server 50 on the external network N.

Description

[Technical field]

[0001] The present invention relates to a network system and a packet relay method that enable a terminal device, which is connected to a closed network and has limited access to devices in an external network, to access an external device under certain conditions. [Background technology]

[0002] Conventionally, medical institutions such as hospitals need to prevent the intrusion of malicious programs into their in-hospital networks from external networks, accidental information leaks to external networks, etc. For this reason, medical institutions, as a rule, make their in-hospital networks closed networks, and limit access to the outside of the medical institution to regional medical cooperation, etc. (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-79712 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in today's information society, there are cases where medical personnel such as doctors wish to access an HTTP server connected to an external network from a terminal device connected to an in-hospital network.

[0005] Furthermore, mechanisms that partially allow access from a closed network to an external network require complex and expensive configurations to ensure a high level of security, and are therefore only implemented in closed networks that require highly skilled engineers and have large-scale facilities.

[0006] For this reason, the issue of how to realize a mechanism that allows access to external networks from the hospital network when necessary while restricting access to external networks is an issue that arises not only in medical institution networks, but also in closed corporate networks that must maintain high security.

[0007] The present invention has been made to solve the problems (issues) associated with the above-mentioned conventional technology, and aims to provide a network system and a packet relay method that enable conditional access to external devices from a terminal device that is connected to a closed network and has limited access to devices in the external network. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the present invention provides a network system having a terminal device connected to a closed network and having restricted access to an external network, a broadband router that enables access to a predetermined HTTP server via the external network, a repeater interposed between the broadband router and the closed network, and a monitoring device that monitors the terminal device, wherein the terminal device is connected to the repeater. was granted to IP address and the HTTP server The domain name was registered Host Table Sending a packet to the repeater using When the repeater receives the packet addressed to itself from the terminal device, Based on a conversion table in which the IP address of the own device and the IP address of the HTTP server are associated, the destination IP address of the packet is converted to the IP address of the HTTP server, and then the packet is The HTTP server To The monitoring device has an acquisition unit that acquires the host table from the terminal device, and an access unit for an authentic HTTP server that can be accessed from the terminal device. A master table of legitimate domain names a storage unit for storing the Domain name and the Valid Domain Name Based on the above, Domain name a determination unit that determines whether the Domain name and a notification unit that issues a predetermined notification when the authentication information is invalid.

[0011] Further, in the above-mentioned invention, the monitoring device is Domain name is not valid, Host Table The apparatus further comprises a deletion instruction unit for issuing an instruction to delete the content.

[0012] The present invention also provides a network system including a terminal device connected to a closed network and restricted in access to an external network, a broadband router that enables access to a predetermined HTTP server via the external network, a repeater that is interposed between the broadband router and the closed network and that is assigned a plurality of IP addresses, and a monitoring device that monitors the terminal device, wherein the terminal device is configured to receive the plurality of IP addresses assigned to the repeater and the IP addresses of the HTTP server corresponding to each IP address. Domain name and but Correspond Registered Host Table Sending a packet to the repeater using When the repeater receives a packet addressed to any one of the multiple IP addresses assigned to the repeater from the terminal device, Based on a conversion table in which the IP address of the own device and the IP address of the HTTP server are associated, the destination IP address of the packet is converted to the IP address of the HTTP server, and then the packet is The HTTP server To The monitoring device has an acquisition unit that acquires the host table from the terminal device, and an access unit for an authentic HTTP server that can be accessed from the terminal device. A master table of legitimate domain names a storage unit for storing the Domain name and the Valid Domain Name Based on the above, Domain name a determination unit that determines whether the Domain name and a notification unit that issues a predetermined notification when the authentication information is invalid.

[0013] The present invention also provides a packet relay method in a network system including a terminal device connected to a closed network and having restricted access to an external network, a broadband router that enables access to a predetermined HTTP server via the external network, a repeater interposed between the broadband router and the closed network, and a monitoring device that monitors the terminal device, the terminal device being connected to the repeater. was granted to IP address and the HTTP server The domain name was registered Host Table A packet is transmitted to the repeater using and if the relay device receives the packet addressed to the relay device from the terminal device, Based on a conversion table in which the IP address of the own device and the IP address of the HTTP server are associated, the destination IP address of the packet is converted to the IP address of the HTTP server, and then the packet is The HTTP server To a relay step of relaying the host table from the terminal device by the monitoring device; an acquisition step of acquiring the host table from the terminal device by the monitoring device; A master table of legitimate domain names a storage step of storing the information in a predetermined storage unit; Domain name and the Valid Domain Name Based on the above, Domain name a determination step of determining whether the Domain name and a notification step of issuing a predetermined notification when the authentication information is invalid. Effect of the Invention

[0014] According to the present invention, it is possible to enable a terminal device, which is connected to a closed network and has limited access to devices in an external network, to access an external device under certain conditions.

[0015] In particular, it will be possible to realize a mechanism that partially allows access from a closed network to an external network using simple, inexpensive equipment and configuration, making it possible for even small medical institutions such as hospitals and clinics to provide conditional connections to external devices from terminal devices connected to the hospital's in-house network, which is a closed network, without the need for the intervention of highly skilled technicians. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing an overview of a network system according to the first embodiment. [Diagram 2] FIG. 2 is an explanatory diagram illustrating packet relay in the network system shown in FIG. [Diagram 3] FIG. 3 is a functional block diagram showing a configuration of the repeater shown in FIG. [Figure 4] FIG. 4 is a functional block diagram showing a configuration of the terminal device shown in FIG. [Diagram 5] FIG. 5 is a sequence diagram illustrating a processing procedure of the network system shown in FIG. [Figure 6] FIG. 6 is a diagram showing an overview of a network system according to the first modification. [Figure 7] FIG. 7 is a diagram illustrating an overview of a network system according to the second embodiment. [Figure 8] FIG. 8 is a functional block diagram showing the configuration of the monitoring device shown in FIG. [Figure 9] FIG. 9 is a flowchart showing a processing procedure of the monitoring device shown in FIG. [Figure 10] FIG. 10 is a functional block diagram showing a configuration of a monitoring device according to the second modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of a network system and a packet relay method according to the present invention will be described in detail with reference to the accompanying drawings.

[0018] [Embodiment 1] <Outline of Network System 10> First, an overview of a network system 10 according to the present embodiment 1 will be described. Here, a network system 10 can be connected to an external network N without installing a DNS (Domain Name System) server in the network system 10, and a network in which a terminal device connected to a closed network A cannot access unnecessary network devices on the external network will be described.

[0019] Fig. 1 is a diagram showing an overview of a network system according to embodiment 1. As shown in Fig. 1, in a network system 10 according to embodiment 1, a repeater 20 is connected to a closed network A, and a plurality of terminal devices 30a, 30b, and 30c (hereinafter, may be collectively referred to as "terminal devices 30") are connected to the closed network A.

[0020] Moreover, the repeater 20 is connected to the broadband router 40 via a closed network B in order to transmit packets received from the closed network A to an external network N. Here, the closed networks A and B are networks constructed using private IP addresses defined by the IETF (Internet Engineering Task Force) and the like. Moreover, the external network N is a network constructed using global IP addresses defined by the IETF and the like.

[0021] The broadband router 40 is connected to an external network N, to which a DNS server 60, an HTTP server 50, etc. are connected.

[0022] The repeater 20 is a device for relaying packets, such as receiving packets sent from a terminal device 30 connected to a closed network A and sending them to an external network N, or receiving packets from an HTTP server 50 or the like connected to the external network N and sending them to a terminal device 30 connected to a closed network A.

[0023] Here, the repeater 20 is assigned two private IP addresses, an IP address 10.128.10.1 / 24 (IP-A) on the closed network A side and a relay private IP address 10.128.10.10 / 24 (IP-B) for relaying packets from the closed network A to the external network N, so that the repeater 20 can be accessed from other network devices connected to the closed network A. The repeater 20 is also assigned a private IP address 192.168.38.100 / 24 ​​(IP-C) on the closed network B side.

[0024] The terminal device 30a is connected to the closed network A and is assigned a private IP address of 10.128.10.100 / 24 ​​(IP-W). The terminal device 30a also stores an FQDN (Fully Qualified Domain Name: domain name) (first connection destination information) and an IP address associated with the domain name in the host table. Here, the relay private IP address of the repeater 20: 10.128.10.10 / 24 is stored for the domain name: www.abc123.com.

[0025] The terminal device 30b is connected to the closed network A and is assigned a private IP address of 10.128.10.101 / 24 (IP-X). The terminal device 30c is also connected to the closed network A and is assigned a private IP address of 10.128.10.102 / 24 (IP-Y).

[0026] The broadband router 40 is a device that relays packets transmitted from the closed network B to a network device on the external network N, and packets sent from a network device on the external network N to the closed network B.

[0027] Specifically, in the case of a packet destined for a network device on the external network N from the closed network B, the broadband router 40 converts the source IP address attached to the packet from a private IP address to a public IP address assigned to the broadband router 40, and transmits the packet to the external network N. In addition, in the case of a packet destined for a network device on the closed network B from a network device on the external network N, the broadband router 40 converts the destination IP address attached to the packet from the public IP address assigned to the broadband router 40 to the private IP address of a network device (e.g., the repeater 20) on the closed network B, and transmits the packet to the closed network B.

[0028] The HTTP server 50 is a Web server that provides a WWW (World Wide Web) service, and is connected to an external network N. The HTTP server 50 has a domain name of www.abc123.com and is assigned a global IP address of 54.211.112.33 (IP-Z).

[0029] The DNS server 60 is a device that, upon receiving a DNS request from another network device, returns the global IP address to which the domain is assigned based on the domain name in the DNS request.

[0030] In the network system 10 according to the first embodiment, for example, when a terminal device 30a wishes to connect to an HTTP server 50, the terminal device 30a transmits a connection request packet to a relay private IP address (IP-B) of the relay device 20 for relaying the packet to an external network N. The relay device 20 then converts the source IP address and destination IP address of the received connection request packet into predetermined IP addresses, and transmits the packet to the HTTP server 50 via the broadband router 40. The response packet from the HTTP server 50 is then transmitted to the terminal device 30a by following the above-mentioned route in reverse.

[0031] 2, when an operator inputs "HTTPS: / / www.abc123.com" into the terminal device 30a and receives a connection request to www.abc123.com (S1), the terminal device 30a refers to the host table (S2). Then, based on the host table, the IP address of www.abc123.com is the relay private IP address of the relay device 20: 10.128.10.10 / 24 (IP-B), so the terminal device 30a creates and transmits a packet with source IP address: IP-W and destination IP address: IP-B (S3).

[0032] The repeater 20 receives a packet from the terminal device 30a (S4). Since the received packet is a packet sent from the terminal device 30a to the relay private IP address: IP-B for relaying to the external network N of the repeater 20, the repeater 20 converts the IP addresses of the source IP address: IP-W and destination IP address: IP-B of the packet sent from the terminal device 30a into source IP address: IP-C and destination IP address: IP-Z (S5). Then, the repeater 20 transmits the address-converted packet to the HTTP server 50 via the broadband router 40 via the broadband router 40 (S6).

[0033] Then, the HTTP server 50 receives the packet from the relay 20 (S7). The response packet from the HTTP server 50 is transmitted to the requesting terminal device 30a by performing address conversion in the reverse order to the above-mentioned process.

[0034] In this way, the network system 10 of the present invention transmits a connection request packet for an HTTP server 50 connected on an external network from a terminal device 30 connected to a closed network A to the relay private IP address of the repeater 20, and the repeater 20 converts the source IP address and destination IP address of the packet into specified IP addresses and transmits it to the HTTP server 50 on the external network, thereby making it possible for the terminal device 30 connected to the closed network A to connect to the HTTP server 50 on the external network N.

[0035] Furthermore, in the network system 10 according to the present invention, even if a terminal device 30 connected to the closed network A makes a connection request to an HTTP server not stored in the host table 35a, the terminal device 30 cannot connect to the HTTP server, thereby preventing accidental information leakage to an external network, etc.

[0036] In particular, it is possible to realize a mechanism that partially allows access from a closed network A to an external network N using simple and inexpensive equipment and configuration, so that even small medical institutions such as hospitals and clinics can provide conditional connections to an HTTP server 50 from terminal devices 30 connected to a closed network (hospital network) A without the need for the intervention of highly skilled technicians.

[0037] <Configuration of repeater 20> Next, the configuration of the repeater 20 shown in Fig. 1 will be described. Fig. 3 is a functional block diagram showing the configuration of the repeater 20 shown in Fig. 1. As shown in Fig. 3, the repeater 20 has a communication I / F unit 23, a storage unit 24, and a control unit 25. The communication I / F unit 23 is a communication interface unit for communicating with the terminal devices 30a, 30b, and 30c via the closed network A and with the broadband router 40 via the closed network B.

[0038] The storage unit 24 is a storage device such as a hard disk drive or a non-volatile memory, and stores a DNS record 24a and relay rule data 24b. The DNS record 24a is data that associates domain names with global IP addresses.

[0039] The relay rule data 24b is data that associates, based on the DNS record 24a, global IP addresses of HTTP servers and the like on the external network N that have been permitted in advance with private IP addresses for packet relay of the relay device 20. For example, in the first embodiment, the private IP address for packet relay of the relay device 20: 10.128.10.10 / 24 and the global IP address of the HTTP server 50: 54.211.112.33 are associated with each other.

[0040] The control unit 25 is a control unit that controls the entire repeater 20, and has a DNS data acquisition unit 25a, a packet receiving unit 25b, an address conversion unit 25c, and a packet transmitting unit 25d. In practice, these programs are loaded into the CPU and executed, causing the DNS data acquisition unit 25a, the packet receiving unit 25b, the address conversion unit 25c, and the packet transmitting unit 25d to execute processes corresponding thereto.

[0041] The DNS data acquisition unit 25a is a processing unit that connects to a DNS server 60 on the external network N and acquires data on a global IP address corresponding to a domain name. The acquired data is stored in the storage unit 24 as a DNS record 24a.

[0042] The packet receiving unit 25b is a processing unit that receives packets sent to the private IP addresses (IP-A, IP-B, IP-C) assigned to the relay device 20.

[0043] The address conversion unit 25c is a processing unit that performs address conversion for the external network N of the source IP address and destination IP address of a packet transmitted to a relay private IP address: IP-B for relaying to the external network N, and address conversion for the closed network A of the source IP address and destination IP address of a packet transmitted from the HTTP server 50 on the external network N. The address conversion in the address conversion unit 25c is performed with reference to the relay rule data 24b.

[0044] As an example, the IP address (source IP address: IP-X, destination IP address: IP-B) of a packet sent from terminal device 30a to an HTTP server 50 on external network N is converted to a relay IP address (source IP address: IP-C, destination IP address: IP-Z).

[0045] In addition, the address conversion unit 25c converts the IP address of the response packet from the HTTP server 50 (source IP address: IP-Z, destination IP address: IP-C) into an IP address for the closed network A (source IP address: IP-B, destination IP address: IP-W).

[0046] The packet transmitting unit 25d is a processing unit that transmits packets that have been address-translated. The repeater 20 may be provided with a repeater unit that integrates the functions of the address converting unit 25c and the packet transmitting unit 25d.

[0047] <Configuration of terminal device 30a> Next, the configuration of the terminal device 30a shown in Fig. 1 will be described. Fig. 4 is a functional block diagram showing the configuration of the terminal device 30a shown in Fig. 1. As shown in Fig. 4, the terminal device 30a has a display unit 31, an input unit 32, a communication I / F unit 34, a storage unit 35, and a control unit 36. The display unit 31 is a display device such as a liquid crystal display that displays various information. The input unit 32 is an input device such as a mouse or keyboard. The communication I / F unit 34 is a communication interface unit for communicating with the repeater 20 via the closed network A.

[0048] The storage unit 35 is a storage device such as a hard disk drive or a non-volatile memory, and stores a host table 35a. The host table 35a is correspondence data between the domain name of the HTTP server and the relay private IP address of the repeater 20. In this example, the relay private IP address: IP-B of the repeater 20 corresponds to the domain name: www.abc123.com of the HTTP server 50 on the external network N.

[0049] The control unit 36 ​​is a control unit that controls the entire terminal device 30a, and includes a reference unit 36a, a packet transmission unit 36b, a packet reception unit 36c, and a display control unit 36d. In practice, these programs are loaded into a CPU and executed, causing the reference unit 36a, the packet transmission unit 36b, the packet reception unit 36c, and the display control unit 36d to execute processes corresponding thereto.

[0050] The reference unit 36a is a processing unit that refers to the host table 35a and acquires a corresponding IP address from the input domain name. The packet sending unit 36b is a processing unit that sends packets. The packet receiving unit 36c is a processing unit that receives packets addressed to the private IP address of the terminal device 30a. The display control unit 36d is a processing unit that controls the display of the contents of the received packets on a predetermined display unit 31.

[0051] The terminal devices 30b and 30c have the same configuration as the terminal device 30a, but the terminal devices 30b and 30c, which do not need to connect to the external network N, do not have a host table 35a in the storage unit 35. When the terminal devices 30b and 30c attempt to access the HTTP server 50 on the external network N and receive an input of a domain name, they are unable to acquire information on the IP address of the connection destination, and so control is exercised to display on the predetermined display unit 31 that connection is not possible.

[0052] <Processing Procedure of Network System 10> Next, a process procedure of the network system 10 shown in Fig. 1 will be described. Fig. 5 is a sequence diagram for explaining the process procedure of the network system 10 shown in Fig. 1. As shown in Fig. 5, the terminal device 30a receives a connection request from an operator to an HTTP server on an external network N (step S101). Then, for the domain name of the HTTP server included in the connection request, the host table 35a is referenced to acquire a corresponding relay private IP address (step S102).

[0053] The terminal device 30a sets the destination IP address of the packet to be transmitted to the address of the relay device 20 (step S103). Then, the terminal device 30a transmits the packet (step S104).

[0054] The relay 20 receives a packet from the terminal device 30a (step S105). Then, the relay 20 converts the address of the packet (step S106). Specifically, the relay 20 converts the source IP address of the received packet to an IP address assigned to the relay 20, and converts the destination IP address to the address of the HTTP server 50 on the external network N. The relay 20 then transmits the packet with the converted address (step S107).

[0055] The HTTP server 50 receives the address-translated packet transmitted from the relay 20 (step S108). Then, the HTTP server 50 creates a response packet corresponding to the received packet (step S109). After that, the HTTP server 50 transmits the response packet (step S110).

[0056] The relay 20 receives the response packet from the HTTP server 50 (step S111). Then, the relay 20 converts the address of the response packet (step S112). Specifically, the relay 20 converts the source IP address of the response packet to a private IP address assigned to the relay 20, and converts the destination IP address to a private IP address assigned to the terminal device 30a.

[0057] After that, the relay device 20 transmits the address-translated packet (step S113). The terminal device 30a receives the packet transmitted by the relay device 20 (step S114).

[0058] As described above, in the first embodiment, the network system 10 includes the relay 20, the terminal devices 30a, 30b, and 30c, and the broadband router 40. When the terminal device 30a connects to an HTTP server on an external network N, the terminal device 30a refers to the host table 35a and transmits a packet to the relay 20, the destination IP address of which is the relay private IP address of the relay corresponding to the domain name. The relay 20 converts the source IP address and destination IP address of the packet transmitted to the relay private IP address into a predetermined IP address and transmits the packet to the HTTP server 50. In addition, the relay 20 converts the source IP address and destination IP address of the packet received from the HTTP server 50 into a predetermined IP address of the closed network A and transmits the packet, thereby enabling the terminal device 30a in the closed network A that does not have a DNS server to connect to the HTTP server 50 on the external network N.

[0059] <Variation 1> In the above-described first embodiment, the relay device 20 assigns one relay IP address. In the modified example, however, a case in which two relay private IP addresses are assigned will be described.

[0060] Fig. 6 is a diagram showing an overview of a network system 70 according to Modification 1. Note that the same components as those in the first embodiment are given the same reference numerals, and detailed description thereof will be omitted. As shown in Fig. 6, in the network system 70, a repeater 20 is connected to a closed network A, and a plurality of terminal devices 30a, 30b, and 30c are connected to the closed network A.

[0061] The repeater 20 is also connected to a broadband router 40 via a closed network B in order to transmit packets received from the closed network A to an external network N. The broadband router 40 is connected to the external network N, and a DNS server 60, an HTTP server 50, an HTTP server 51, etc. are also connected to the external network N.

[0062] To allow other network devices connected to the closed network A to access the repeater 20, the repeater 20 is assigned an IP address 10.128.10.1 / 24 (IP-A) on the closed network A side, and two relay private IP addresses (IP address 10.128.10.10 / 24 (IP-B), IP address 10.128.10.11 / 24 (IP-D)) for relaying packets from the closed network A to the external network N. The repeater 20 is also assigned a private IP address 192.168.38.100 / 24 ​​(IP-C) on the closed network B side.

[0063] The terminal device 30a is connected to the closed network A and is assigned a private IP address of 10.128.10.100 / 24 ​​(IP-W). The terminal device 30a also stores a domain name and a relay private IP address associated with the domain name in the host table. Here, the IP address: 10.128.10.10 / 24 is stored for the domain name: www.abc123.com, and the IP address: 10.128.10.11 / 24 is stored for the domain name: www.def345.co.jp.

[0064] When connecting from the terminal device 30a to the HTTP server 50, the terminal device 30a transmits a connection request packet to a relay private IP address (IP-B) for relaying the packet to the HTTP server 50 on the external network N of the relay device 20. The relay device 20 then converts the source IP address and destination IP address of the received connection request packet and transmits the packet to the HTTP server 50 via the broadband router 40. The response packet from the HTTP server 50 is then transmitted to the terminal device 30a by following the above-mentioned route in reverse.

[0065] Furthermore, when connecting from the terminal device 30a to the HTTP server 51, the terminal device 30a transmits a connection request packet to a relay private IP address (IP-D) for relaying the packet to the HTTP server 51 on the external network N of the relay device 20. The relay device 20 then converts the source IP address and destination IP address of the received connection request packet and transmits the packet to the HTTP server 51 via the broadband router 40. The response packet from the HTTP server 51 is then transmitted to the terminal device 30a by following the above-mentioned route in reverse.

[0066] In the above-mentioned variant example 1, the relay device 20 is described as assigning two relay private IP addresses to access the HTTP server on the external network N, but the number of relay private IP addresses may be three or more.

[0067] [Embodiment 2] <Outline of Network System 90> In the above embodiment 1, the case where the host table 35a is stored in the terminal device 30a has been described. In embodiment 2, however, a case where the validity of the host table 35a stored in the terminal device 30a is monitored will be described.

[0068] Fig. 7 is a diagram showing an overview of a network system 90 according to the second embodiment. Note that the same components as those in the first embodiment are given the same reference numerals, and detailed description thereof will be omitted. As shown in Fig. 7, in the network system 90 according to the second embodiment, a repeater 20 is connected to a closed network A, and a plurality of terminal devices 30a, 30b, and 30c and a monitoring device 80 are connected to the closed network A.

[0069] The repeater 20 is also connected to a broadband router 40 via a closed network B in order to transmit packets received from the closed network A to an external network N. The broadband router 40 is connected to the external network N, and a DNS server 60, an HTTP server 50, etc. are also connected to the external network N.

[0070] The monitoring device 80 stores a master host table 84a that stores valid domain names (second connection destination information) of HTTP servers or the like that have been permitted to be accessed in advance, and relay private IP addresses of the relay device 20 that correspond to the valid domain names. The monitoring device 80 then acquires the host table 35a stored in the terminal device 30, compares it with the master host table 84a, and judges whether the data in the host table 35a stored in the terminal device 30 is valid. If the monitoring device 80 judges that the data is invalid, it notifies the terminal device 30 that the host table 35a is invalid.

[0071] <Configuration of monitoring device 80> Next, the configuration of the monitoring device 80 shown in Fig. 7 will be described. Fig. 8 is a functional block diagram showing the configuration of the monitoring device 80 shown in Fig. 7. As shown in Fig. 8, the monitoring device 80 has a communication I / F unit 83, a storage unit 84, and a control unit 85, and is connected to a display unit 81 and an input unit 82. The display unit 81 is a display device such as a liquid crystal display that displays various information. The input unit 82 is an input device such as a mouse or keyboard. The communication I / F unit 83 is a communication interface unit for communicating with the terminal devices 30a, 30b, and 30c via the closed network A.

[0072] The storage unit 84 is a storage device such as a hard disk drive or a non-volatile memory, and stores a master host table 84a. The master host table 84a is data that corresponds to the domain names of HTTP servers that are permitted to be connected in advance, and the relay private IP addresses that are assigned to the relay device 20 for connecting to the domains.

[0073] The control unit 85 is a control unit that controls the entire monitoring device 80, and has a host table acquisition unit 85a, a determination unit 85b, and a notification unit 85c. In practice, these programs are loaded into a CPU and executed, causing the host table acquisition unit 85a, the determination unit 85b, and the notification unit 85c to execute processes corresponding to each of them.

[0074] The host table acquisition unit 85a is a processing unit that acquires the host table 35a stored in the terminal device 30 connected to the closed network A.

[0075] The judgment unit 85b is a processing unit that compares the domain name (first connection destination information) contained in the host table 35a of the acquired terminal device 30 with the valid domain name (second connection destination information) contained in the master host table 84a, and judges the validity of the host table 35a.

[0076] The notification unit 85c is a processing unit that notifies the terminal device 30 of a warning when the determination result of the determination unit 85b is "invalid". When making a warning, the notification unit 85c connects to the terminal device 30 that makes the warning, and displays the warning on a predetermined display unit 31 of the terminal device 30 by using a message command or the like.

[0077] Next, the processing procedure of the monitoring device 80 will be described. Fig. 9 is a flowchart showing the processing procedure of the monitoring device 80 shown in Fig. 8. As shown in Fig. 9, the monitoring device 80 acquires the host table of the terminal device 30 (step S201). Then, the monitoring device 80 compares the master host table with the host table (S202).

[0078] Thereafter, the monitoring device 80 judges the validity of the host table based on the comparison result (step S203). If the judgment result is "valid" (step S203: Yes), the monitoring device 80 ends the series of processes. On the other hand, if the judgment result is "invalid" (step S203: No), the monitoring device 80 issues a warning to the terminal device 30 (step S204).

[0079] As described above, in this embodiment 2, the monitoring device 80 is connected to the closed network A, and the host table 35a of the terminal device 30 is compared with a predetermined master host table 84a to determine whether it is valid, thereby preventing an operator from tampering with the host table 35a of the terminal device 30.

[0080] <Variation 2> In the above embodiment 2, the monitoring device 80 issues a warning to the terminal device 30 if the host table 35a of the terminal device 30 is invalid. However, in variant example 2, a case will be described in which the monitoring device 80 issues a warning and also instructs the terminal device 30 to delete the host table 35a.

[0081] Fig. 10 is a functional block diagram for explaining the configuration of a monitoring device 100 according to Modification 2. As shown in Fig. 10, the monitoring device 100 has a communication I / F unit 83, a storage unit 84, and a control unit 85, and is connected to a display unit 81 and an input unit 82.

[0082] The control unit 105 is a control unit that controls the entire monitoring device 100, and has a host table acquisition unit 85a, a determination unit 85b, a notification unit 85c, and a deletion instruction unit 105a. In reality, these programs are loaded into the CPU and executed, thereby causing the host table acquisition unit 85a, the determination unit 85b, the notification unit 85c, and the deletion instruction unit 105a to execute processes corresponding to each of them.

[0083] The deletion instruction unit 105a is a processing unit that, when the determination result of the determination unit 85b is determined to be "inauthentic", accesses the terminal device 30 and instructs the deletion of the host table 35a stored in the storage unit 35 of the terminal device 30. When issuing a deletion instruction, the deletion instruction unit 105a connects to the terminal device 30 that issues the deletion instruction, and displays a deletion instruction message on a predetermined display unit 31 of the terminal device 30 using a message command or the like.

[0084] In the above embodiments 1 and 2, the terminal device 30 accepts a domain name and refers to the host table 35a to set the destination IP address to the relay private IP address. However, the terminal device 30 may directly accept the relay private IP address of the repeater 20, set it to the destination IP address, and transmit a packet to the repeater 20.

[0085] In addition, in the above-mentioned embodiments 1 and 2, the case where there is only one repeater 20 has been described, but it is also possible to install two repeaters 20, one as an active device and the other as a backup device, and perform alive monitoring so that if the active device fails, the backup device takes over the functions.

[0086] In addition, in the above embodiments 1 and 2, the repeater 20 converts the source IP address and destination IP address into a specified IP address, but it may also be configured to enable multiple access using a specified IP address and port number by applying IP masquerading technology.

[0087] In the above embodiment 2, the monitoring device 80 determines legitimacy by comparing the domain name (first connection destination information) included in the host table 35a of the terminal device 30 with the valid domain name (second connection destination information) included in the master host table 84a of the monitoring device 80. However, the monitoring device 80 may also determine legitimacy by comparing the IP address and domain name in the host table 35a of the terminal device 30 with the IP address and valid domain name in the master host table 84a of the monitoring device 80.

[0088] The configurations illustrated in the above embodiments are merely functional schematics, and are not necessarily physically configured as illustrated. In other words, the form of distribution and integration of each device is not limited to that illustrated, and all or part of the devices can be functionally or physically distributed and integrated in any unit according to various loads, usage conditions, etc. [Industrial Applicability]

[0089] The network system and packet relay method according to the present invention are suitable for cases where a terminal device that is connected to a closed network and has restricted access to devices in an external network is allowed to access an external device under certain conditions. [Explanation of symbols]

[0090] 10 Network Systems 20 Repeater 23 Communication I / F section 24 Memory section 24a DNS Records 24b Relay rule data 25 Control Unit 25a DNS data acquisition section 25b Packet receiver 25c Address conversion unit 25d Packet transmitter 30, 30a, 30b, 30c Terminal device 31 Display section 32 Input section 34 Communication I / F section 35 Storage section 35a Host Table 36 Control Unit 36a Reference section 36b Packet transmitter 36c Packet receiver 36d Display control unit 36d 40 Broadband Router 50, 51 HTTP Server 60 DNS Servers 70 Network Systems 80 Monitoring equipment 81 Display section 82 Input section 83 Communication I / F section 84 Memory section 84a Master Host Table 85 Control Unit 85a Host table acquisition section 85b Judgment part 85c Notification Department 90 Network Systems 100 Monitoring equipment 105 Control section 105a Deletion instruction section A, B Closed network N External Network

Claims

1. A network system comprising: a terminal device connected to a closed network and having restricted access to an external network; a broadband router that enables access to a specific HTTP server via the external network; a repeater that is interposed between the broadband router and the closed network; and a monitoring device that monitors the terminal device, The terminal device Transmitting a packet to the relay using a host table in which the IP address assigned to the relay and the domain name of the HTTP server are registered; The repeater includes: When the packet addressed to the device itself is received from the terminal device, the device converts the destination IP address of the packet into the IP address of the HTTP server based on a conversion table in which the IP address of the device itself is associated with the IP address of the HTTP server, and then relays the packet to the HTTP server; The monitoring device includes: an acquisition unit that acquires the host table from the terminal device; a storage unit that stores a master table in which legitimate domain names of legitimate HTTP servers that can be accessed from the terminal device are registered; a determination unit that determines whether or not the domain name is legitimate based on the domain name acquired by the acquisition unit and the legitimate domain name stored in the storage unit; a notification unit that issues a predetermined notification when the domain name is invalid; A network system comprising:

2. The monitoring device includes:

2. The network system according to claim 1, further comprising a deletion instruction unit that instructs said terminal device to delete said host table when said domain name is invalid.

3. A network system comprising: a terminal device connected to a closed network and having restricted access to an external network; a broadband router that enables access to a specific HTTP server via the external network; a repeater that is provided with a plurality of IP addresses and is located between the broadband router and the closed network; and a monitoring device that monitors the terminal device, The terminal device Transmitting a packet to the relay using a host table in which the plurality of IP addresses assigned to the relay and the domain names of the HTTP servers corresponding to each IP address are registered in association with each other; The repeater includes: When a packet addressed to one of a plurality of IP addresses assigned to the relay is received from the terminal device, the relay converts the destination IP address of the packet to the IP address of the HTTP server based on a conversion table in which the IP address of the relay device corresponds to the IP address of the HTTP server, and then relays the packet to the HTTP server; The monitoring device includes: an acquisition unit that acquires the host table from the terminal device; a storage unit that stores a master table in which legitimate domain names of legitimate HTTP servers that can be accessed from the terminal device are registered; a determination unit that determines whether or not the domain name is legitimate based on the domain name acquired by the acquisition unit and the legitimate domain name stored in the storage unit; a notification unit that issues a predetermined notification when the domain name is invalid; A network system comprising:

4. A packet relay method in a network system including a terminal device connected to a closed network and having restricted access to an external network, a broadband router that enables access to a specific HTTP server via the external network, a repeater interposed between the broadband router and the closed network, and a monitoring device that monitors the terminal device, comprising: a transmission step in which the terminal device transmits a packet to the relay by using a host table in which an IP address assigned to the relay and a domain name of the HTTP server are registered; a relay step of, when the relay receives the packet addressed to itself from the terminal device, converting the destination IP address of the packet into the IP address of the HTTP server based on a conversion table in which the IP address of the relay device corresponds to the IP address of the HTTP server, and then relaying the packet to the HTTP server; an acquisition step in which the monitoring device acquires the host table from the terminal device; a storage step in which the monitoring device stores in a predetermined storage unit a master table in which legitimate domain names of legitimate HTTP servers accessible from the terminal device are registered; a determination step in which the monitoring device determines whether or not the domain name is legitimate based on the domain name acquired in the acquisition step and the legitimate domain name stored in the storage unit; a notification step of issuing a predetermined notification when the domain name is invalid; A packet relay method comprising:

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