JP2005328373A - Network security system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a network security system capable of previously defending illegal attack to a server apparatus always connected to a network and having high security. <P>SOLUTION: A DNS server provided with an IP address storage part 36 for storing an IP address correspondingly to a domain name, an IP address change rule storage part 32 for storing a plurality of IP address change rules, an IP address change rule changing part 33 for selecting one of change rules and changing a current change rule, an IP address changing part 34 for changing an IP address by the selected change rule, and a user authentication part 35 for authenticating whether a client terminal has been registered or not is connected to the Internet so that only a registrant can acquire IP addresses which are sequentially changed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a network security system, and more particularly to a technique for preventing an unauthorized attack against a server in a client / server system.

  2. Description of the Related Art Conventionally, a client / server system requests a service from a client terminal to the server device via the Internet, and the server device provides a content distribution service to the client terminal that has requested the service via the Internet. In this case, the client terminal inputs the domain name instead of the IP address assigned to the server device. Then, the IP address corresponding to the domain name is returned from the DNS server (database storing the correspondence between the IP address assigned to each server device connected to the Internet and the domain name), and this IP address is used as a destination server. By accessing the apparatus, communication with the server apparatus is established, and a content distribution service of the server apparatus can be received (see, for example, Patent Document 1).

JP 2004-102410 A

  However, in the conventional client / server system, the IP address of the server device is fixed. Even if the IP address of the server device is changed, the changed IP address is notified to the administrator of the DNS server, and the domain name is associated with the changed IP address. Therefore, in the conventional client / server system, anyone can know the IP address of the server device by entering the domain name, and a malicious attacker can easily access the server device. It is. For this reason, for example, by executing a program that centrally accesses a specific server, the server is rendered incapable of providing services, or attacks that exploit security holes (vulnerabilities) in the server device. There is a problem that it is easily attacked by a malicious attacker.

  In addition, as a countermeasure against attacks that attack security holes, at present, the developer who developed the software creates and distributes software (patches) to deal with security holes, and applies the patches to repair the security holes. However, in most cases, security holes are often found by being attacked, and it is not possible to prevent unauthorized attacks against server devices in advance.

  The present invention has been made paying attention to the above problems, and by appropriately changing the IP address of the server device and allowing only a specific user to know the changed IP address, It is an object of the present invention to provide a network security system that can prevent an unauthorized attack on the server device in advance and improve the security of the server device.

  Therefore, the present invention is a network security system for protecting the information providing server device from an unauthorized attack on the information providing server device connected to the network, wherein the information accessed from the client terminal via the network A plurality of IP address change rules corresponding to the domain name of the providing server device, a change rule for selecting one of the plurality of change rules, changing the IP address with the selected change rule, and selecting the change rule The IP address changed according to the change rule can be acquired only by a client terminal registered in advance.

  In this configuration, the IP address of the information providing server device is changed by a change rule selected from among a plurality of change rules, and the change rule for changing the IP address is also changed. For this reason, the IP address corresponding to the domain name of the information providing server device is sequentially changed, and only the client terminal registered in advance can obtain the changed IP address. It is difficult for an unregistered attacker who wants to perform a simple attack to obtain the IP address of the information providing server device.

  Specifically, as in claim 2, an IP address storage unit that stores an IP address in association with a domain name of the information providing server device, and the change rule for the IP address stored in the IP address storage unit A plurality of IP address change rule storage units, a rule change unit for selecting one of the plurality of change rules stored in the IP address change rule storage unit and changing the change rule, and the rule change unit An IP address changing unit for changing the IP address of the IP address storage unit based on the selected change rule, and a client terminal authenticating unit for authenticating whether or not the client terminal is registered in advance are provided on the network. Only the client terminal that has been authenticated by the client terminal authentication unit can acquire the changed IP address.

  In this case, as in claim 3, a DNS server device including an IP address storage unit, an IP address change rule storage unit, a rule change unit, an IP address change unit, and a client terminal authentication unit is provided on the network, When the DNS server device changes the IP address of the IP address storage unit at the IP address changing unit, the DNS server device notifies the information providing server device of the changed IP address via the network, while registering at the client terminal authentication unit The information providing server device stores and holds the notified IP address, and the client terminal receives the received IP address. It may be configured to access the information providing server device by an address.

  According to a fourth aspect of the present invention, an address providing server device including an IP address change rule storage unit, a rule change unit, an IP address change unit, and a client terminal authentication unit is provided on the network, and the address providing server device includes: The IP address changed by the IP address changing unit is transmitted to the server device for providing information via the network, and the changed IP address and domain name are transmitted to the client terminal authenticated by the client terminal authenticating unit. The information providing server device stores and holds the transmitted IP address, while the client terminal includes the IP address storage unit and receives the received IP address from the address providing server device. The IP address based on the correspondence data between the IP address and the domain name. Update the IP address of the storage unit may be configured to access the updated IP address in the information-providing server device.

  According to a fifth aspect of the present invention, a rule change server device including an IP address change rule storage unit, a rule change unit, and a client terminal authentication unit is provided on the network, and the rule change server device includes the rule change unit. The change rule changed in step (b) is transmitted to the information providing server device and the client terminal authenticated by the client terminal authentication unit via the network, and the information providing server device is configured to transmit the address change. And an IP address holding unit, the IP address is changed by the address changing unit based on the transmitted change rule, the changed IP address is stored and held by the IP address holding unit, and the client terminal An IP address change unit and the IP address storage unit, and based on the transmitted change rule The IP address changing unit synchronized with the IP address changing unit of the information providing server device changes the IP address to update the IP address of the IP address storage unit, and the updated IP address is used for the information providing server device. It is good also as a structure to access.

  As described above, according to the network security system of the present invention, the IP address corresponding to the domain name of the information providing server device is changed according to the change rule, and the change rule is changed as appropriate. Since the configuration is such that only pre-registered registrants can obtain it, an unregistered attacker who intends to attack the information providing server device illegally may obtain an IP address corresponding to the domain name of the information providing server device. It is difficult and can protect the information providing server device from an unregistered unauthorized attacker in advance, and the security of the information providing server device can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic diagram of a first embodiment of a network security system according to the present invention.

  1, the network security system according to the present embodiment includes a client terminal 10 connected to the Internet 1 as a network, an information providing server device 20 that provides services to the client terminal 10, and an information providing server device 20. It includes a DNS server device 30 that is a database that manages the correspondence between domain names and IP addresses. It goes without saying that the client terminal 10 and the information providing server device 20 are not limited to one and are connected in large numbers on the Internet 1.

  The client terminal 10 is generally an information device having an Internet connection function, such as a normal personal computer, mobile terminal, mobile phone, game machine, etc. As shown in FIG. 2, a control unit 11 and an input operation unit 12 are provided. A user ID and password storage unit 13 and a communication unit 14. The control unit 11 controls the overall operation of the client terminal 10 such as the input operation unit 12, the user ID / password storage unit 13, and the communication unit 14. The input operation unit 12 is for inputting a domain name or the like with a keyboard or the like, for example. The user ID and password storage unit 13 stores an authentication user ID and password issued from the server device administrator to the registrant in order to receive the services of the information providing server device 20 and the DNS server device 30. Thus, the user ID and password entered once are stored and held in order to save the trouble of inputting each time the connection destination is changed. The communication unit 14 is for connecting the client terminal 10 to the Internet 1 for information communication.

  The information providing server device 20 is a server device having a normal configuration for performing information distribution and the like, as shown in FIG. 3, a control unit 21, a content storage unit 22, an IP address holding unit 23, And a communication unit 24. The control unit 21 performs overall control of the entire information providing server device 20 such as the content storage unit 22, the IP address holding unit 23, and the communication unit 24. The content storage unit 22 stores contents such as normal Web to be provided to the client terminal 10. The IP address holding unit 23 holds its own IP address notified from the DNS server device 30. The communication unit 14 is for connecting the information providing server device 20 to the Internet 1 for information communication.

  The DNS server device 30 is a database that holds correspondence data between the domain name of the information providing server device 20 and the IP address. The DNS server device 30 appropriately changes the IP address of the information providing server device 20 and allows registered users who have registered in advance. As shown in FIG. 4, the control unit 31, the IP address change rule storage unit 32, the IP address change rule change unit 33, the IP address change unit 34, A user authentication unit 35, an IP address storage unit 36, and a communication unit 37 are provided. The control unit 31 includes an IP address change rule storage unit 32, an IP address change rule change unit 33 that is a rule change unit, an IP address change unit 34, a user authentication unit 35 as a client terminal authentication unit, an IP address storage unit 36, and a communication The overall control of the DNS server device 30 such as the unit 37 is performed. The IP address change rule storage unit 32 stores at least two types of change rules for changing the IP address at appropriate time intervals. The IP address change rule changing unit 33 appropriately selects one of a plurality of change rules stored in advance in the IP address change rule storage unit 32. The IP address changing unit 34 changes the IP address according to the change rule selected by the IP address change rule changing unit 33. The user authentication unit 35 executes an authentication process as to whether or not the user is a registrant when accessed from the client terminal 10. The IP address storage unit 36 stores correspondence data between the domain name of the information providing server device 20 and the IP address. When the IP address is changed by the IP address changing unit 34, the set IP address is changed. Rewrite and update to address. The communication unit 37 is for connecting the DNS server device 30 to the Internet 1 for information communication.

Next, the operation until communication is established between the client terminal 10 and the information providing server device 20 in the first embodiment will be described based on the flowchart of FIG.
In step 1 (indicated by S1 in the figure, the same applies hereinafter), an IP address transmission request is generated from the client terminal 10 to the DNS server device 30.
In step 2, the DNS server device 30 that has received the IP address transmission request of the client terminal 10 generates a transmission request for the user ID and password to the client terminal 10.

In step 3, the client terminal 10 that has received the user ID and password transmission request of the DNS server device 30 operates the input operation unit 12 to input the user ID and password, or from the user ID and password storage unit 13. Read or send the user ID and password.
In step 4, the DNS server device 30 that has received the user ID and password determines whether or not the received user ID and password are registered in the user authentication unit 35 by checking against the data in the database of the registrant. If it is authenticated as a registered regular user (YES), the process proceeds to step 5. If it is determined that it is not registered (NO), the process is terminated and access is denied. If it is determined that the user ID has not been registered, the user ID and password may be input again. If the user cannot authenticate the preset number of times, the user ID may be determined to be unregistered and access may be denied.

In step 5, the DNS server device 30 transmits an access permission signal to the client terminal 10.
In step 6, the domain name of the information providing server device 20 is transmitted from the client terminal 10 that has received the access permission signal to the DNS server device 30.
In step 7, the DNS server device 30 that has received the domain name searches the IP address corresponding to the received domain name from the stored data in the IP address storage unit 36 and transmits it to the client terminal 10. This IP address is appropriately changed by the IP address changing process of the DNS server device 30 as shown in the flowchart of FIG.

  In step 8, the client terminal 10 that has received the IP address from the DNS server device 30 accesses the information providing server device 20 using the received IP address. As a result, a connection is established between the client terminal 10 and the information providing server device 20 via the Internet 1, and the content details stored in the content storage unit 22 of the information providing server device 20 on the client terminal 10 side. Can be browsed.

Next, IP address change processing in the DNS server device 30 will be described with reference to the flowchart of FIG.
The change of the IP address is changed by the IP address changing unit 34 based on the changing rule selected from the IP address changing rule storing unit 32 by the IP address changing rule changing unit 33 and stored in the IP address storing unit 36.
First, when the IP address is changed, in step 11, a timer that counts the time until the next IP address change starts counting time.

In step 12, it is determined whether or not the timer is up, that is, whether or not the timer value has reached a predetermined value. If YES, the process proceeds to step 13.
In step 13, the IP address is changed.
In step 14, the current IP address stored in the IP address storage unit 36 is rewritten with the IP address changed in step 13.
In step 15, the information providing server device 20 is notified of the rewritten IP address.
Until the change rule is changed, the operations in steps 11 to 15 are repeated, and the IP addresses are changed one after another at predetermined time intervals. Note that the information providing server device 20 stores and holds the notified IP address in the IP address holding unit 23.

  The IP address change rule is set for each information providing server device 20 connected to the Internet 1. Accordingly, the DNS server device 30 has a plurality of change rules for each information providing server device 20, and the information providing server device 20 is changed according to the change rules set for each information providing server device 20. An IP address change process is performed, and the changed IP address is notified to the information providing server device 20 whose IP address has been changed.

In the present embodiment, the change rule when changing the IP address is also changed as appropriate as shown in the flowchart of FIG.
The change rule changing process will be described with reference to the flowchart of FIG.
In step 21, it is determined whether or not a change rule change command has been issued. If the determination is yes, go to step 22. The change command may be given from the outside, or may be generated when the time is measured by a timer.

In step 22, the IP address change rule changing unit 33 selects one change rule other than the currently used change rule from the IP address change rule storage unit 32 and notifies the IP address changing unit 34 of the change rule.
In step 23, the IP address changing unit 34 rewrites the IP address in the IP address storage unit 36 by executing the operations in steps 13 to 15 in FIG. 6 in accordance with the notified change rule, and sends it to the corresponding information providing server device 20. Notice. Thereafter, the IP address change process shown in FIG. 6 is executed according to the change rule selected this time until the next change rule change command is issued.

  According to the network security system of the first embodiment, only the registered user can acquire the IP address from the DNS server device 30, and the IP address of the information providing server device 20 is changed one after another, and the change rule Since the configuration is also changed, it is difficult for an unregistered user to know the IP address of the information providing server device 20, and the information providing server device 20 that is always connected to the Internet 1 is protected from unauthorized attacks in advance. The security of the client / server system can be improved.

  With IPv6, which is the next IP standard, there is no worry that the IP address will run out even if one information providing server device holds (registers) multiple IP addresses, and the IP address of each information providing server device is changed sequentially. It is possible to do. Also, since the amount of IP addresses is enormous, the IP address changing algorithm is also difficult to decipher. Therefore, the network security system of this embodiment is extremely effective for improving the security of the server device.

Next, a second embodiment of the present invention will be described.
FIG. 8 shows a schematic diagram of the second embodiment. In addition, the same code | symbol is attached | subjected to the same element as 1st Embodiment, and description is abbreviate | omitted.
In FIG. 8, the network security system of the second embodiment is configured to include a client terminal 40, an information providing server device 50, and a rule change server device 60 that are connected to the Internet 1.

  The client terminal 40 of this embodiment includes an IP address change function and a domain name-IP address storage function in addition to the same functions as those of the first embodiment. As shown in FIG. In addition to the input operation unit 42, the user ID / password storage unit 43, and the communication unit 44, an IP address change rule holding unit 45, an IP address change unit 46, and an IP address storage unit 47 are provided. The IP address change rule holding unit 45 stores and holds the change rule transmitted from the rule change server device 60. Note that the IP address changing unit 46 and the IP address storage unit 47 have the same functions as those provided in the DNS server device 30 of the first embodiment, and a description thereof will be omitted.

  The information providing server device 50 is provided with an IP address changing function in the same manner as the client terminal 40 in addition to the same functions as in the first embodiment. As shown in FIG. In addition to the unit 52, the IP address holding unit 53 and the communication unit 54, an IP address IP address change rule holding unit 55 and an IP address changing unit 56 are provided. Then, the IP address changing unit 56 of the information providing server device 50 and the IP address changing unit 46 of the client terminal 40 change the IP address in synchronization with each other.

  As shown in FIG. 11, the rule change server device 60 includes a control unit 61, an IP address change rule storage unit 62, an IP address change rule change unit 63, a user authentication unit 64, and a communication unit 65. The IP address change rule is changed, and the changed change rule is transmitted to the client terminal 40 and the information providing server device 50, respectively. The rule change server device 60 stores a plurality of IP address change rules for each information providing server device 50 connected to the Internet 1.

  In the change rule change process of the rule change server device 60 of this embodiment, as shown in the flowchart of FIG. 12, it is determined in step 31 whether or not a change rule change command has been issued. In step 32, the IP address change rule changing unit 63 selects one new change rule from the IP address change rule storage unit 62, and in step 33, the IP address change rule changing unit 63 operates to notify the information providing server device 50.

Next, an operation until communication is established between the client terminal 40 and the information providing server device 50 in the second embodiment will be described based on the flowchart of FIG.
In step 41, an IP address change rule transmission request is generated from the client terminal 40 to the rule change server device 60.
In step 42, the rule change server device 60 that has received the change rule transmission request from the client terminal 40 generates a user ID and password transmission request to the client terminal 40.

In step 43, the client terminal 40 that has received the user ID and password transmission request of the rule change server device 60 operates the input operation unit 42 to input the user ID and password, or the user ID and password storage unit 43. Or read the user ID and password.
When the rule change server device 60 receives the user ID and password in step 44, the user authentication unit 64 determines whether or not the user ID and password are registered, and authenticates the registered regular user ( YES), go to step 45. If it is determined that it is not registered (NO), the process is terminated and access is denied.

In step 45, the rule change server device 60 transmits to the client terminal 40 the change rule currently selected in the change rule change process of FIG. 12 and notified to the information providing server device 50.
In step 46, the client terminal 40 stores and holds the received change rule in the IP address change rule holding unit 55.

  In step 47, the IP address changing unit 46 of the client terminal 40 executes the IP address changing process in steps 11 to 14 in FIG. 6 according to the change rule stored and held in the IP address change rule holding unit 55. The IP address change rule holding unit 55 of the information providing server device 50 stores and holds the same change rule notified from the rule change server device 60 in the change rule change processing of FIG. The IP address changing process 40 is executed in synchronization with the IP address changing process of the information providing server device 50.

  In step 48, when the domain name is input at the client terminal 40, the IP address corresponding to the input domain name is searched from the stored data in the IP address storage unit 47, and the information providing server device 50 is searched with the searched IP address. To access. As a result, a connection is established between the client terminal 40 and the information providing server device 50 via the Internet 1, and it is possible to browse the contents provided by the information providing server device 50.

  According to the network security system of the second embodiment, only the registered user can acquire the IP address change rule from the rule change server device 60, and the change rule provided by the rule change server device 60 can be changed as appropriate. Therefore, as in the first embodiment, it is difficult for an unregistered user to know the IP address of the information providing server device 50, and the information providing server device 50 always connected to the Internet 1 is illegally attacked. The security of the client / server system can be improved.

  In the second embodiment, the rule change server device 60 transmits a change rule to the client terminal 40 when the client terminal 40 makes a change rule transmission request to the client terminal 40, and the information providing server device. 50 is automatically notified every time a change rule is changed, but a transmission request is sent from the client terminal 40 and the information providing server device 50 to the rule change server device 60 at regular timing intervals. Then, the client terminal 40 and the information providing server device 50 may acquire the change rule, respectively.

Next, a third embodiment of the present invention will be described.
FIG. 14 shows a schematic diagram of the third embodiment. In addition, the same code | symbol is attached | subjected to the same element as 1st Embodiment, and description is abbreviate | omitted.
In FIG. 14, the network security system according to the third embodiment is configured to include a client terminal 70, an information providing server device 20, and an address providing server device 80 connected to the Internet 1.

The client terminal 70 of this embodiment has a domain name-IP address storage function in addition to the same functions as those of the first embodiment. As shown in FIG. 15, the control unit 71, the input operation unit 72, the user In addition to the ID and password storage unit 73 and the communication unit 74, an IP address storage unit 75 is provided. The IP address storage unit 75 stores domain name-IP address correspondence data acquired from the address providing server device 80.
The information providing server device 20 has the same configuration as that of the first embodiment shown in FIG.

  The address providing server device 80 has a configuration obtained by removing the IP address storage unit 36 from the configuration of the DNS server device 30 of the first embodiment. As shown in FIG. 16, a control unit 81 and an IP address change rule storage unit 82 are provided. And an IP address change rule change unit 83, an IP address change unit 84, a user authentication unit 85, and a communication unit 86. When the IP address is changed, correspondence data between the changed IP address and the domain name is displayed. The data is transmitted to the client terminal 70.

The IP address changing process of the address providing server device 80 according to the present embodiment will be described with reference to the flowchart of FIG. 17. In step 51, a timer that counts the time until the next IP address change starts counting time, and in step 52. If it is determined that the timer has expired, the IP address is changed at step 53, and the correspondence data between the changed IP address and domain name is temporarily stored in a temporary storage memory (not shown) at step 54. In addition, the corresponding IP server 20 is notified of the IP address changed in step 55.
Note that the address providing server device 80 also changes the IP address change rule as appropriate in the same manner as the change rule change process of FIG.

Next, an operation until communication is established between the client terminal 70 and the information providing server device 20 in the third embodiment will be described based on the flowchart of FIG.
In step 61, an access request is transmitted from the client terminal 70 to the address providing server device 80.
In step 62, the address providing server device 80 that has received the access request generates a user ID and password transmission request to the client terminal 70.

In step 63, the client terminal 70 that has received the user ID and password transmission request of the access providing server device 80 transmits the user ID and password.
In step 64, the access providing server device 80 determines whether or not the received user ID and password are registered, and proceeds to step 65 if it is authenticated as a registered regular user (YES). If it is determined that it is not registered (NO), the process is terminated and access is denied.

In step 65, the access providing server device 80 transmits the correspondence data between the domain name and the IP address, which are changed and temporarily stored in the IP address changing process of FIG.
In step 66, the client terminal 70 rewrites and updates the data stored in the IP address storage unit 75 based on the received correspondence data.

  In step 67, the client terminal 70 converts the domain name input by the input operation unit 72 into an IP address using the data stored in the IP address storage unit 75 and accesses the information providing server device 20. As a result, a connection is established between the client terminal 70 and the information providing server device 20 via the Internet 1, and it is possible to browse the contents provided by the information providing server device 20.

  According to the network security system of the third embodiment, only the registered user can acquire the correspondence data between the domain name and the IP address of the information providing server device 20, and the address providing server device 80 uses the change rule to change the IP address. Since the configuration is such that the change rule is appropriately changed, it is difficult for an unregistered user to know the IP address of the information providing server device 20 as in the first and second embodiments. The information providing server device 20 always connected to the Internet 1 can be protected in advance from unauthorized attacks, and the security of the client / server system can be improved.

1 is a schematic diagram showing a first embodiment of a network security system of the present invention. Configuration diagram of client terminal of the first embodiment 1 is a configuration diagram of an information providing server device according to a first embodiment. Configuration diagram of DNS server device of first embodiment The flowchart explaining the communication establishment operation | movement of the client terminal of 1st Embodiment, and the server apparatus for information provision Flowchart explaining operation of IP address change processing Flowchart explaining operation of change rule change processing Schematic diagram showing a second embodiment of the network security system of the present invention. Configuration diagram of client terminal of second embodiment Configuration diagram of server device for providing information of second embodiment The block diagram of the rule change server apparatus of 2nd Embodiment Flowchart explaining change rule change processing operation of rule change server device The flowchart explaining the communication establishment operation | movement of the client terminal of 2nd Embodiment, and the server apparatus for information provision Schematic diagram showing a third embodiment of the network security system of the present invention. Configuration diagram of client terminal of third embodiment The block diagram of the address provision server apparatus of 3rd Embodiment Flowchart explaining IP address change processing operation of address providing server device The flowchart explaining the communication establishment operation | movement of the client terminal of 3rd Embodiment, and the server apparatus for information provision

Explanation of symbols

1 Internet 10, 40, 70 Client terminal 20, 50 Information providing server device 23, 53 IP address holding unit 30 DNS server device 31 Control unit 32, 62, 82 IP address change rule storage unit 33, 63, 83 IP address change Rule change unit 34, 46, 56, 84 IP address change unit 35, 47, 75 IP address storage unit 36 User authentication unit 45, 55 IP address change rule holding unit 60 Rule change server device 80 Address providing server device

Claims (5)

A network security system for protecting the information providing server device from an unauthorized attack on the information providing server device connected to the network,
A plurality of IP address change rules corresponding to the domain name of the information providing server device accessed from the client terminal via the network are selected, and one of the plurality of change rules is selected and the selected change rule is used. While changing the IP address and changing the change rule to be selected as appropriate,
A network security system characterized in that only a client terminal registered in advance can acquire an IP address changed according to the change rule. An IP address storage unit for storing the IP address in association with the domain name of the information providing server device;
An IP address change rule storage unit for storing a plurality of the change rules for the IP address stored in the IP address storage unit;
A rule changing unit for selecting one of the plurality of change rules stored in the IP address change rule storage unit and changing the change rule;
An IP address changing unit that changes the IP address of the IP address storage unit based on the change rule selected by the rule changing unit;
A client terminal authenticating unit for authenticating whether or not the client terminal is registered in advance on the network;
The network security system according to claim 1, wherein only the client terminal that is authenticated by the client terminal authentication unit can acquire the changed IP address. A DNS server device including an IP address storage unit, an IP address change rule storage unit, a rule change unit, an IP address change unit, and a client terminal authentication unit is provided on the network,
The DNS server device notifies the information providing server device of the changed IP address via the network when the IP address changing unit changes the IP address of the IP address storage unit, while the client terminal authenticating unit A configuration capable of transmitting the IP address of the IP address storage unit to a client terminal that has been authenticated as registered,
The information providing server device stores and holds the notified IP address;
The network security system according to claim 2, wherein the client terminal is configured to access the information providing server device using the received IP address. An address providing server device including an IP address change rule storage unit, a rule change unit, an IP address change unit, and a client terminal authentication unit is provided on the network.
The address providing server device transmits the IP address changed by the IP address changing unit to the information providing server device via the network, while changing to a client terminal authenticated by the client terminal authenticating unit. Configured to transmit the correspondence data between the IP address and the domain name,
While the information providing server device stores and holds the transmitted IP address,
The client terminal includes the IP address storage unit, updates the IP address of the IP address storage unit based on correspondence data between the IP address and the domain name received from the address providing server device, and stores information using the updated IP address. The network security system according to claim 2, wherein the network security system is configured to access the providing server device. A rule change server device comprising an IP address change rule storage unit, a rule change unit and a client terminal authentication unit is provided on the network,
The rule change server device is configured to transmit the change rule changed by the rule change unit to the client terminal that has been authenticated by the information providing server device and the client terminal authentication unit via the network, respectively.
The information providing server device includes the address changing unit and an IP address holding unit, changes the IP address by the address changing unit based on the transmitted change rule, and changes the changed IP address to the IP address holding unit. And keep it in memory,
The client terminal includes the IP address changing unit and the IP address storage unit, and the IP address changing unit synchronized with the IP address changing unit of the information providing server device based on the transmitted change rule is an IP address. The network security system according to claim 2, wherein the IP address of the IP address storage unit is updated by changing the IP address and the information providing server device is accessed by the updated IP address.

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