Unauthorized access prevention method, unauthorized access prevention apparatus and unauthorized access prevention program

1. An unauthorized access prevention method, comprising:

receiving a signaling packet for starting a session from a device connected to the network;

detecting whether the signaling packet received from the device connected to a network contains a description for unauthorized access;

discarding a signaling packet which apparently contains a description for unauthorized access;

deleting descriptions of other items from the signaling packet which does not apparently contain the description for unauthorized access, while leaving descriptions of predetermined items including at least a description of a desired port number indicating a port number desired to be used in the session at the signaling packet which does not apparently contain the description for unauthorized access; and

transmitting the signaling packet obtained after the deletion is conducted to a signaling packet processing unit.

2. The unauthorized access prevention method according to claim 1 , wherein transmission of the signaling packet obtained after the deletion is conducted to the signaling packet processing unit is conducted in response to polling.

3. The unauthorized access prevention method according to claim 1 , further comprising:

receiving a response packet, responding to the signaling packet, from the signaling packet processing unit, the response packet containing an available port number indicating a port number which can be used by a session unit to conduct the session;

translating the available port number to a different port number; and

transmitting the response packet with the available port number translated to the different port number to the device connected to the network.

4. The unauthorized access prevention method according to claim 3 , further comprising:

receiving a session packet using a port having the different port number contained in the response packet transmitted to the device connected to the network, from the device connected to the network;

detecting whether or not the session packet is a packet according to a predetermined protocol;

discarding the session packet if the session packet is not a packet according to a predetermined protocol; and

conducting reverse translation on a port number in the session packet judged to be a packet according to a predetermined protocol, thereby obtaining a port number before translation, and transmitting a resultant session packet to the session unit.

5. The unauthorized access prevention method according to claim 3 , wherein instead of or in addition to translating the available port number to a different port number, an available fourth layer protocol number indicating a fourth layer protocol number which can be used in the session is translated to a different fourth layer protocol number.

6. An unauthorized access prevention apparatus, comprising:

means for receiving a signaling packet for starting a session from a device connected to a network;

means for detecting whether or not the signaling packet received from the device connected to the network contains a description for unauthorized access;

means for discarding a signaling packet which apparently contains a description for unauthorized access;

means for deleting descriptions of other items from the signaling packet which does not apparently contain the description for unauthorized access, while leaving descriptions of predetermined items including at least a description of a desired port number indicating a port number desired to be used in the session at the signaling packet which does not apparently contain the description for unauthorized access; and

means for transmitting the signaling packet obtained after the deletion is conducted to a signaling packet processing unit.

7. The unauthorized access prevention apparatus according to claim 6 , wherein transmission of the signaling packet obtained after the deletion is conducted to the signaling packet processing unit is conducted in response to polling.

8. The unauthorized access prevention apparatus according to claim 6 , further comprising:

means for receiving a response packet, responding to the signaling packet, from the signaling packet processing unit, the response packet containing an available port number indicating a port number which can be used by a session unit to conduct the session;

means for translating the available port number to a different port number; and

means for transmitting the response packet with the available port number translated to the different port number to the device connected to the network.

9. The unauthorized access prevention apparatus according to claim 8 , further comprising:

means for receiving a session packet using a port having the different port number contained in the response packet transmitted to the device connected to the network, from the device connected to the network;

means for detecting whether or not the session packet is a packet according to a predetermined protocol;

means for discarding the session packet if the session packet is not a packet according to a predetermined protocol; and

means for conducting reverse translation on a port number in the session packet judged to be a packet according to a predetermined protocol, thereby obtain a port number before translation, and transmit a resultant session packet to the session unit.

10. The unauthorized access prevention apparatus according to claim 8 , wherein instead of or in addition to translating the available port number to a different port number, an available fourth layer protocol number indicating a fourth layer protocol number which can be used in the session is translated to a different fourth layer protocol number.

11. A non-transitory computer readable medium storing computer instructions for causing a computer executing the instructions to perform an unauthorized access prevention method, comprising:

receiving a signaling packet for starting a session from a device connected to a network;

detecting whether the signaling packet received from the device connected to the network contains a description for unauthorized access;

discarding a signaling packet which apparently contains a description for unauthorized access;

deleting descriptions of other items from the signaling packet which does not apparently contain the description for unauthorized access, while leaving descriptions of predetermined items including at least a description of a desired port number indicating a port number desired to be used in the session at the signaling packet which does not apparently contain the description for unauthorized access; and

transmitting the signaling packet obtained after the deletion is conducted to a signaling packet processing unit.

12. The computer readable medium according to claim 11 , wherein transmission of the signaling packet obtained after the deletion is conducted to the signaling packet processing unit is conducted in response to polling.

13. The computer readable medium according to claim 11 , wherein said method further comprises:

receiving a response packet, responding to the signaling packet, from the signaling packet processing unit, the response packet containing an available port number indicating a port number which can be used by a session unit to conduct the session;

translating the available port number to a different port number; and

transmitting the response packet with the available port number translated to the different port number to the device connected to the network.

14. The computer readable medium according to claim 13 , wherein said method further comprises:

receiving a session packet using a port having the different port number contained in the response packet transmitted to the device connected to the network, from the device connected to the network;

detecting whether or not the session packet is a packet according to a predetermined protocol;

discarding the session packet if the session packet is not a packet according to a predetermined protocol; and

conducting reverse translation on a port number in the session packet judged to be a packet according to a predetermined protocol, thereby obtaining a port number before translation, and transmitting a resultant session packet to the session unit.

15. The computer readable medium according to claim 13 , wherein instead of or in addition to translating the available port number to a different port number, an available fourth layer protocol number indicating a fourth layer protocol number which can be used in the session is translated to a different fourth layer protocol number.

16. The unauthorized access prevention method according to claim 1 , wherein said detecting whether the signaling packet received from the device connected to the network contains a description for unauthorized access comprises detecting whether the signaling packet contains a computer virus pattern.

17. The unauthorized access prevention apparatus according to claim 6 , wherein said detecting whether the signaling packet received from the device connected to the network contains a description for unauthorized access comprises detecting whether the signaling packet contains a computer virus pattern.

18. The computer readable medium according to claim 11 , wherein said detecting whether the signaling packet received from the device connected to the network contains a description for unauthorized access comprises detecting whether the signaling packet contains a computer virus pattern.