Abstract:
A communication control apparatus includes a storage device configured to store corresponding weighted values for each of a plurality of predetermined portions of a sender address, a connection request receiver configured to receive a connection request packet including a connection request, a weight detector configured to obtain a weighted value corresponding to a part of the sender address assigned to the connection request packet from among the weighted values stored in the storage device, a connection controller configured to reject the connection request, when the obtained weighted value exceeds a predetermined value, by determining that a communication apparatus consumes more than a predetermined amount of a resource and discarding the connection request packet, and allow the connection request when the obtained weighted value falls within a predetermined range that is lower than the predetermined value, a weight updater configured to update the weighted values, and a packet transmitter.

Description:
RELATED APPLICATIONS 
   The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2003-045957 filed on Feb. 24, 2003, which is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a communication control apparatus, a communication control method and a communication control program product, to restrict the processing of inappropriate connection requests in an environment in which IPv6 addresses are used. 
   2. Description of the Related Art 
   The largest computer network, i.e., the Internet, can be accessed and employed worldwide by the public to utilize information and services, provided by a variety of companies for users having Internet access, and to develop new businesses. As a result, a progress made in Internet development and the advancement of new Internet usage techniques has become remarkable. In the Internet, each terminal has an identifier, an IP address that is used for exchanging packets. As an example, pursuant to Transmission Control Protocol (TCP) (see IETF RFC793 Transmission Control Protocol, Darpa Internet Program, Protocol Specification, September, 1981), four items are required to identify a connection, i.e., for a transmitter and receiver connection, an IP address and a port number are required for each terminal. And since TCP is a connection type protocol, these four items, at the least, must be stored in each terminal when a TCP connection is established. Thus, a malicious user may be able to employ the characteristic arrangement to establish an illegal connection, and to mount an attack to deplete the hardware and software resources (hereinafter referred to simply as resources) of a target terminal. 
   According to the currently employed Internet Protocol version 4 (IPv4), the address space is configured in 32 bits, and as the address is depleted, the number of addresses available for allocation for each user became drastically reduced. Therefore, for the same IP address, the number of available accesses is limited to prevent a resource depleting attack. 
   Recently, however, Internet protocol version 6 (IPv6) (see IETF RFC2460 Internet Protocol, Version 6(IPv6) Specification, December, 1998) has been developed and put into practical use, and for IPv6 the address space has been expanded to 128 bits. 
   Since for IPv6 the address space has been expanded to 128 bits, a network can accommodate 64-bit addresses when IPv6 is used. But while, for IPv6, the use of this wide address space confers many advantages, the size of the address space facilitates its effective use by an malicious user. That is, when the malicious user is able to connect his or her terminal connected to a specific network, by using the address width, substantially 64 bits, the user can attempt to attack on a target terminal. Further, since according to IPv6 an individual terminal is permitted to accommodate a plurality of networks, a wider address space may be allocated. Therefore, with IPv6, the attack by an malicious user to deplete resources can not be avoided simply by comparing addresses, a conventional procedure employed with IPv4. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention is to provide a communication control apparatus, a communication control method and a communication control program product. 
   In order to achieve the object, according to a first aspect of the invention, there is provided a communication control apparatus including: a connection request receiver configured to receive a connection request for connecting to a server from a specific communication apparatus connected to a network; a storage device configured to store information concerning an identifier for the specific communication apparatus, the information included in the connection request; a first detector configured to determine whether or not the identifier falls within a predetermined range; a second detector configured to determine whether the connection request consumes a predetermined amount or more of communication resources; and a connection controller configured to restrict the connection request received from other communication apparatuses that includes identifiers falling within the predetermined range as the identifier of the specific communication apparatus, when the second detector determines that the connection request consumes the predetermined amount or more of the communication resources. 
   According to a second aspect of the invention, there is provided a communication control method including: receiving a connection request for connecting to a server from a specific communication apparatus connected to a network; storing information concerning an identifier for the specific communication apparatus, the information included in the connection request; determining whether or not the identifier falls within a predetermined range; determining whether the connection request consumes a predetermined amount or more of communication resources; and restricting the connection request received from other communication apparatuses that includes identifiers falling within the predetermined range as the identifier of the specific communication apparatus, when the connection request is determined to consume the predetermined amount or more of the communication resources. 
   According to a third aspect of the invention, there is provided a communication control program product for causing a computer, which is located between a specific communication apparatus connected to a network and a server that performs a server process and a communication process, to execute procedures including: means for receiving a connection request for connecting to a server from a specific communication apparatus connected to a network; means for storing information concerning an identifier for the specific communication apparatus, the information included in the connection request; means for determining whether or not the identifier falls within a predetermined range; means for determining whether the connection request consumes a predetermined amount or more of communication resources; and means for restricting the connection request received from other communication apparatuses that includes identifiers falling within the predetermined range as the identifier of the specific communication apparatus, when the connection request is determined to consume the predetermined amount or more of the communication resources. 
   According to a fourth aspect of the invention, there is provided a communication control program product for causing a computer, which performs a server process and a communication process for a specific communication apparatus connected thereto via a network, to execute procedures including: means for receiving a connection request for connecting to a server from a specific communication apparatus connected to a network; means for storing information concerning an identifier for the specific communication apparatus, the information included in the connection request; means for determining whether or not the identifier falls within a predetermined range; means for determining whether the connection request consumes a predetermined amount or more of communication resources; and means for restricting the connection request received from other communication apparatuses that includes identifiers falling within the predetermined range as the identifier of the specific communication apparatus, when the connection request is determined to consume the predetermined amount or more of the communication resources. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
       FIG. 1  is a schematic diagram showing a system employing a communication control apparatus according to a first embodiment of the invention; 
       FIG. 2  is a diagram showing the configuration of the communication control apparatus according to the first embodiment; 
       FIG. 3  is a diagram showing the data structure of an IPv6 address; 
       FIG. 4  is a diagram showing the data structure of the IPv6 address; 
       FIG. 5  is diagram showing weight data stored in a weight storage device; 
       FIG. 6  is a diagram showing weight determination data stored in a weight determination storage device; 
       FIG. 7  is a flowchart showing the operation of the communication control apparatus; 
       FIG. 8  is a diagram showing the configuration of a server implementing communication control according to a second embodiment of the invention; 
       FIG. 9  is a diagram showing weight history data stored in a weight history storage device; 
       FIG. 10  is a flowchart showing the operation of the server implementing communication control; and 
       FIG. 11  is a diagram showing a weight management table prepared by performing hash calculations. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the accompanying drawings, a description will be given in detail of embodiments of the invention. 
   First Embodiment 
   &lt;Communication Connection System&gt; 
   As is shown in  FIG. 1 , a communication connection system according to a first embodiment of the invention includes: a communication control apparatus  100 ; a communication server  1 ; communication apparatuses  2   a  and  2   b  connected to a LAN cable  2 ; a communication apparatus  3   a  connected to a LAN cable  3 ; a communication apparatus  4   a  connected to a LAN cable  4 ; a communication apparatus  5   a  connected to a LAN cable  5 ; and a network  6  for connecting these communication apparatuses to the communication server  1 . The network  6  is a communication network, such as the Internet, for performing data transmission through a communication medium, regardless of a wireless or wire medium. 
   The communication apparatuses  2   a ,  2   b ,  3   a ,  4   a  and  5   a , respectively connected to the LAN cables  2 ,  3 ,  4  and  5 , request connections to the communication server  1 . In the connecting, the communication control apparatus  100  monitors the connection to determine whether one of the communication apparatuses  2   a ,  2   b ,  3   a ,  4   a  and  5   a  frequently and unnecessarily issues connection requests and employs a large amount of software resources (simply, “resources”) of the communication server  1 . During the monitoring process, the communication control apparatus  1  adds a “weight” to a transmission source address for a packet, and employs the weighted address to measure the deviation of the transmission sources for the packet, i.e., each time a packet that consumes resources is received from the same transmission source, the communication control apparatus  100  increases the weight of the transmission source address. Further, in accordance with the weight, the communication control apparatus  100  decides which processing to perform for each of the transmitting packet. For example, when a packet has a very heavy weight, the communication control apparatus  100  determines that the packet was sent from a communication apparatus that has frequently issued unnecessary connection requests, the communication control apparatus  100  abandons the connection request from the communication apparatus, instead of transmitting it to the communication server  1 . It should be noted that the function of the communication control apparatus  100  is carried out by installing in a computer a software program that provides the pertinent function. 
   &lt;Communication Control Apparatus&gt; 
   As shown in  FIG. 2 , the communication control apparatus  100  according to the first embodiment of the invention includes: a storage device  10 , an input device  11 , a communication control apparatus  13 , a main storage device  14  and a processor (CPU)  15 . The storage device  10  includes a received packet storage device  16 , a resource storage device  17 , a packet segmentation storage device  18 , a weight storage device  19 , a weight determination storage device  20 , and a server process storage device  33 . 
   The received packet storage device  16  temporarily stores packets received from the communication apparatuses  2   a ,  2   b ,  3   a ,  4   a  and  5   a  requesting connections. The resource storage device  17  stores resource category data for a received packet. 
   The packet segmentation storage device  18  stores an address structure for defining the segmentation position of an address held by a packet. The weight storage device  19 , as shown in  FIG. 5 , stores the current weight of a packet segment, and a weighting variable for each packet segment and the weight obtained by the weighting. The weight determination storage device  20  stores a reference value table for determining whether the detected weight is a reference value, or larger or smaller, and also to store a process to be performed for the packet based on the determination results. The server process storage device  33  stores a program executed by the CPU  15 . 
   The CPU  15  includes a connection request receiver  15   a , a resource detector  15   b , an address segmentation unit  15   c , a weight detector  15   d , a connection controller  15   c , a weight addition unit  15   f  and a packet transmitter  15   g.    
   The connection request receiver  15   a  is a module for receiving connection requests issued by the communication apparatuses  2   a ,  2   b ,  3   a ,  4   a  and  5   a . The resource detector  15   b  corresponds to a first detector of the invention, i.e., a module for detecting the resources for a received packet. When a received packet is a synchronize flag packet (SYN packet), the resource detector  15   b  determines that the resource category for the SYN packet is TCP because the SYN packet indicates it is a request for establishing a TCP connection. The address segmentation unit  15   c  then splits the received packet, based on the packet segmentation data stored in the packet segmentation storage device  18 , by referring to the feature of the address structure. For an example in  FIG. 3 , a packet of 128 bits is simply split, at the 48-th bit and the 64-th bit, into three segments, i.e., a P 1  area of 48 bits, a P 2  area of 16 bits and a P 3  area of 64 bits. In an example in  FIG. 4 , a packet is split into three segments at the 48-th bit and the 64-th bit and, beginning with the first bit, a cumulative value, is obtained. Thus, the P 1  area of 48 bits, the P 2  area of 64 bits and the P 3  area of 128 bits are obtained. 
   The weight detector  15   d  corresponds to a second detector of the invention, i.e., a module for determining whether a connection request will consume a predetermined amount or more, and for determining whether information concerning an address, which is stored in the storage device  10 , is based on the address of the communication apparatus or a communication apparatus that belongs to a neighboring network. Specifically, the weight detector  15   d  employs the data in the weight storage device  19  to detect the weight of the transmission source address for a received packet, and employs the weight to determine whether the packet will consume a constant amount of resources or more, or was received from the same communication apparatus or a communication apparatus that belongs to a neighboring network. Since the upper network portion of an IPv6 address can be rewritten, a packet may be transmitted from the unauthorized communication apparatus by using a false address indicating a neighboring network. The connection controller  15   e  is a module for employing the detected weight of the transmission source address to determine whether the transmission source should be connected to the communication server  1 . The weight addition unit  15   f  is a module for, in a case where it is ascertained that the weight of the transmission source address falls within an appropriate range and the packet is therefore transmitted to the communication server  1 , adding a new weight to the weight of the transmission source address. The packet transmitter  15   g  is a module for transmitting, to the communication server  1 , the received packet for which the connection is permitted, e.g., the SYN packet. 
   The input device  11  is an interface for receiving packets, such as SYN packets, from the communication apparatuses  2   a ,  2   b ,  3   a ,  4   a  and  5   a . The output device  12  is an interface for transmitting, to the communication server  1 , packets such as SYN packets for which a connection is permitted. The communication control apparatus  13  generates a control signal for exchanging a packet with a router and a node, such as another communication apparatus, using wireless communication or a wire communication line. The main storage device  14  is used to temporarily store program data wherein the procedures are written and packet data to be processed, and from the main storage device  14 , machine instructions for the program or the data are transmitted upon the reception of a request from the CPU  15 . The main storage device  14  and the CPU  15  are interconnected by an address bus, a data bus and a control signal line. 
   (Communication Control Method) 
   The operation of the communication control apparatus  100  will now be described while referring to  FIG. 7 . 
   In step S 101 , the connection request receiver  15   a  of the communication control apparatus  100  receives a packet from the communication apparatus  2   a ,  2   b ,  3   a ,  4   a  or  5   a , and temporarily stores the packet in the received packet storage device  16 . 
   In step S 102 , the resource detector  15   b  extracts a packet that is temporarily stored in the received packet storage device  16 , and detects the resource category for this packet. When the packet is an SYN packet, the resource detector  15   b  determines that the resource category for the packet is the TCP resource category. 
   In step S 103 , the address segmentation unit  15   c  employs the data in the packet segmentation storage device  18  to split the transmission source address of the received packet into segments, as shown in  FIGS. 3 and 4 . 
   In step S 104 , the weight detector  15   d  employs the data in the weight storage device  19  to detect the weight of each segment of the received packet, e.g., the current weights “P 1 : 1 , P 2 : 2  and P 3 : 3 ”, of the segments shown as (a) in  FIG. 5 , that are stored in the weight storage device  19 . 
   In step S 105 , the connection controller  15   e  determines whether the current weight of each segment that is detected falls within a reference value. The reference value is previously set. 
   When the connection controller  15   e  determines that the weight falls within the reference value, in step S 106 , the connection controller  15   e  decides what transmission process to be applied for the packet having a specific characteristic even though the weight of the packet is within the reference value. The transmission process to be applied is decided based on the reference value table in the weight determination storage device  20  in  FIG. 6 . One example of the deciding of the transmission process will be described hereinafter. When a weight of the packet differs largely while the weight is within the reference value during a unit time period, i.e., when over a short period of time packets are collectively received from a specific communication apparatus, the connection controller  15   e  determines that the probability of malicious activity is high, and greatly delays the transmission of the packet to the communication server  1 . When the weight of the packet is larger than the current weight average, i.e., when the number of times packets are received is slightly greater than that for another communication apparatus, the connection controller  15   e  determines that the probability of malicious activity is low, and slightly delays the transmission of the packet to the communication server  1 . When the weight is smaller than the average weight, the transmission of the packet is performed at normal speed. 
   In step S 107 , the weight addition unit  15   f  adds the weight of the packet based on the “weight” and a “weighting variable for a segment” that are stored in the weight storage device  19 . The weighting variable is employed for the addition and multiplication of the reference weight, and the weighting variables for segments P 1 , P 2  and P 3  may be equal, or greater weighting may be provided for one segment. For an IPv6 address, the network prefix portion (P 1 +P 2 ) in  FIGS. 3 and 4  employs a variable length for specifying an upper network. Whereas, since the interface ID portion (P 3 ) is prepared based on MAC addresses uniquely provided for the communication apparatuses  2   a ,  2   b ,  3   a ,  4   a  and  5   a , the communication apparatuses  2   a ,  2   b ,  3   a ,  4   a  and  5   a  can be identified. That is, when P 1  and P 1 +P 2  are the same for the packet, it can be assumed that the packet originated at a communication apparatus that is present in the same or a neighboring network, and when P 1 +P 2 +P 3  are the same, it can be assumed that the packet originated at the same communication apparatus. Therefore, it is preferable that weighting be performed in the manner represented by P 1 ≦P 2 ≦P 3 . As shown as (c) in  FIG. 5 , the weights obtained through the weighting process are P 1 : 1(1*1), P 2 : 2(1*2) and P 3 : 6(2*3). 
   Before the calculation of the weight, an inquiry may be issued to the communication server  1 , as for all transmission source addresses for which resources are currently being consumed, and a communication apparatus for which it is determined the probability it will mount an attack is high may be specified and its address stored in the received packet storage device  16 . 
   Finally, in step S 108 , the packet transmitter  15   g  transmits to the communication server  1  the packet. 
   Since the communication control apparatus  100  in the first embodiment of the invention performs the resource detection and the weight detection, the authorization of the packet transmission source can be examined. Further, based on the verification, the connection controller can limit connection requests, e.g., the reception of an inappropriate connection request may be rejected, so that the mounting, by a malicious user, of an attack for depleting the resources can be avoided. 
   The communication control apparatus  100  may be embedded in a bridge or a router. Further, in order to protect the communication server  1 , the communication control apparatus  100  may employ another unique method to process a packet addressed to the communication server  1 , or may notify the communication server  1  of the weight of a received packet. For the notification, a method can be employed for rewriting the value of a flow label or a traffic class. In addition, the communication control apparatus  100  may employ a service management method such as DiffServ (Differentiated Servicess), to control the traffic to the communication server  1 . As an example, when a party in charge of maintenance for the communication server  1  and the communication control apparatus  100  and a party that mounts an attack belong to neighboring networks, the attack is mounted even when the communication control using the weighting is exercised. Therefore, the communication control apparatus may include an area for accepting the connection request so long as a specific condition is satisfied, regardless of the weight. As a specific method, so long as IP sec is correctly performed, the connection request is received even from the “heavy” transmission source address. In this case, it is more effective to use the system explained in a second embodiment, wherein the communication control apparatus  100  is mounted in the communication server  1 . 
   Second Embodiment 
   &lt;Communication Connection System&gt; 
   A server  200  implementing communication control that is equivalent to the server  1  wherein the communication control apparatus  100  in  FIG. 1  is mounted is described hereinafter as a second embodiment of the invention. Since the other apparatuses are the same as those for the communication connection system of the communication control apparatus  100  in  FIG. 1 , no further explanation for them will be given. 
   &lt;Server Implementing Communication Control&gt; 
   As is shown in  FIG. 8 , the server  200  implementing communication control according to the second embodiment includes: a storage device  40 , an input device  21 , an output device  22 , a communication control apparatus  23 , a main storage device  24  and a processor (CPU)  25 . 
   The storage device  40  includes a received packet storage device  26 , a resource storage device  27 , a packet segmentation storage device  28 , a weight storage device  29 , a weight determination storage device  30 , a program storage device  31 , a weight history storage device  32  and a server process storage device  33 . 
   As is shown in  FIG. 9 , the weight history storage device  32  is used to store, for each unit time period, changes in the weight of packets received from a transmission source that belongs to the same or a neighboring network, i.e., the history of the weights. 
   The server process storage device  33  is used to store information required to establish a normal client server connection, and to perform a constant service process for a communication terminal. 
   The CPU  25  includes a connection request receiver  25   a , a resource detector  25   b , an address segmentation unit  25   c , a weight detector  25   d , a connection controller  25   e , a weight addition unit  25   f , a weight subtraction unit  25   g , a connection response transmitter  25   h  and a server processor  25   i . The weight subtraction unit  25   g  is a module for reducing the weight of a transmission source address when it is ascertained that the weight of the source address falls within an appropriate range and a packet is transmitted to the communication server  1 . The server processor  25   i  is a module for establishing a normal client server connection, and for performing a constant service process for a communication terminal. Since the other units are the same as those for the first embodiment, no further explanation for them will be given. 
   &lt;Communication Control Method&gt; 
   The operation of the server  200  implementing communication control will now be described while referring to  FIG. 10 . 
   In step S 201 , the connection request receiver  25   a  of the server  200  receives a packet from the communication apparatuses  2   a ,  2   b ,  3   a ,  4   a  or  5   a , and temporarily stores the packet in the received packet storage device  26 . 
   In step S 202 , the resource detector  25   b  extracts a packet that is temporarily stored in the received packet storage device  26 , and detects the resource category for this packet. 
   In step S 203 , the address segmentation unit  25   c  employs the information in the packet segmentation storage device  28  to split the transmission source address of the received packet into the segments shown in  FIGS. 3 and 4 . 
   In step S 204 , the weight detector  25   d  employs the data in the weight storage device  29  to detect the weight of each segment in the received packet. 
   In step S 205 , the weight detector  25   d  employs the data in the weight history storage device  32  to detect the history of the weight of each segment in the received packet. 
   In step S 206 , the connection controller  25   e  determines whether the weight of the currently detected segment falls within a reference value. The reference value is set in advance. Further, the connection controller  25   e  determines whether the history of the weight is appropriate. In this determination, for example, the connection controller  25   e  determines whether the weight is the result of a number of packets exceeding the normal range being received, over a period of several seconds, from a communication apparatus that belongs to the same or a neighboring network, or is simply the result of packets within the normal range being received. 
   When in step S 206  the weight falls within the reference value and the weight history is normal, it is assumed in step S 207  that, for some reason, merely connection requests were concentrated on over a constant period of time, and the weight subtraction unit  25   g  reduces the weight of the packet. 
   When the weight falls within the reference value in step S 206 , in step S 208  the weight addition unit  25   f  adds the weight of the packet. The weighting is performed based on the “weight” and the “weighting variable of a segment” that are stored in the weight storage device  29 . 
   When, in step S 206 , the weight exceeds the reference value and the weight history is abnormal, it is assumed in step S 209  that the communication apparatus at the packet transmission source has mounted a malicious attack and the packet is abandoned. 
   In step S 207 , the server processor  25   i  creates a connection response packet, such as an acknowledgement (ACK) packet or an ACK/SYN packet. 
   In step S 210 , even when the weight falls within the reference value in steps S 207  and S 208 , the data in the weight determination storage device in  FIG. 6  are employed to set the processing condition employed by the server processor  25   i  for a packet it has been found has a specific characteristic. Thereafter, in step S 211  the connection response transmitter  25   h  transmits the connection response packet to the transmission source address for the received packet. 
   According to the server  200  according to the second embodiment in which implementing communication control, since the detection of the resource, the weight and the weight history is performed, whether the packet transmission source is authorized and whether the source has mounted a malicious attack can be specifically examined. Further, based on the examination results, the connection controller can impose limits on the acceptance of connection requests, e.g., a request by a malisious user for an inappropriate connection can be rejected, so that the mounting of a malicious attack to deplete resources can be avoided. 
   Since the server  200  includes the communication control function and the server function, responsibility can easily be assigned for the security associated with determining the authorization for the IPsec payload. Therefore, as one example method, even if an attack is mounted when the side responsible for the maintenance of the communication server and the communication control apparatus and the side mounting an attack thereon belong to neighboring networks, so long as the attack satisfies a specific condition, the connection request is accepted, regardless of the weight. Specifically, so long as the IPsec is correctly performed, even a connection request from a “heavy” transmission source address is accepted. 
   &lt;Example Weight Calculation&gt; 
   For a communication server that receives many connection requests from the communication apparatuses  2   a ,  2   b ,  3   a ,  4   a  and  5   a , the ratio for the weighting process is greatly increased. Therefore, a preferable method is for the weight to be approximately but efficiently calculated, even when there is a slight shift in the weight. As an example, a calculation method employing a hash table will be explained while referring to  FIG. 11 . 
   First, for a specific packet, hash tables for P 1 , P 2  and P 3  are prepared. In the hash tables, a calculation is performed to obtain values for P 1 , P 2  and P 3 , which are represented by a small, finite bit length “k”. That is, the index value for the array in the hash table is defined as “k”. Thereafter, the value H(P 1 ) obtained by performing a calculation for P 1 , the value H(P 2 ) obtained by performing a calculation for P 2  and the value H(P 3 ) obtained by performing a calculation for P 3  are entered in the array. When the numerical values for the P 1 , P 2  and P 3  addresses are simply split, as shown in  FIG. 3 , for the calculations, a hash table having a tree structure is prepared. But when, as shown in  FIG. 4 , the numerical values for the P 1 , P 2  and P 3  addresses have been accumulated, three hash tables, one each for P 1 , P 2  and P 3 , are prepared. 
   The number of times (equals to the value of the weight in the embodiment) whereby the hash calculation was passed through the area P 1  is written in the hash table for P 1 . That is, the number of times the calculation was passed through the same array in the hash table is directly employed as the value for the weight. When the index for the array is 3, and includes addresses (0) (1) and (2), and when the calculation was passed through address (1) one time, a weight of 1 is entered in the hash table. When the calculation was passed through address (2) two times, a weight of 2 is entered in the hash table. And when the calculation was passed through address (3) three times, a weight of 3 is entered in the hash table. Then, the value for the weight is added to a weight storage area (not shown) and stored. The value for this weight is defined as W 1 . 
   Further, the position (e.g., the pointer to the pertinent area) in the hash table for H(P 2 ) is entered in the hash table of P 1 . In accordance with this position, the operation is shifted to the next hash table H(P 2 ). 
   In the hash table for P 2 , the number of times (equals the value of the weight) the hash calculation was passed through the pertinent area is entered. Then, the value of the weight is added to the weight storage area (not shown) and stored. This weight value is defined as W 2 . In addition, the position (e.g., the pointer to the pertinent table) in the hash table H(P 3 ) is written in the hash table for P 2 . In accordance with this position, the operation is shifted to the hash table H(P 3 ). 
   In the hash table for P 3 , the number of times (equals the value of the weight) the hash calculation was passed through the pertinent area is entered. Then, the value of the weight is added to the weight storage area (not shown) and stored. This weight value is defined as W 3 . 
   That is, the weighting variables for the segments shown as (b) in  FIG. 5  are employed, and a weight represented by the following Equation (1) is entered in the weight storage area. 
   
     
       
         
             
           
             
               
                 
                   
                     
                       
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                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
   
   For the weight detection, the weights of the individual areas W 1 , W 2  and W 3  may be calculated. In this example, the weights are simply increased by the same amount, and the calculation of the weight is performed while taking weighting into account as shown in Equation (2).
 
weight= W 1*1+( W 2*2)+( W 3*3)  Equation (2)
 
   Another method may simply be obtained, by increasing the weight while taking the addition of the weights into account as shown in Equation (3).
 
weight= W 1 +W 2 +W 3  Equation (3)
 
   Furthermore, when a received packet is regarded as a packet for releasing resources, e.g., an FIN packet for which the resource category is TCP, the weight of the transmission source address for this packet is reduced. For the weight reduction, the same method may be employed as is used for increasing the weight, or another method may be employed. 
   Since the weight calculation method in the embodiment is employed to detect the weight, whether the packet transmission source is authorized or whether a malicious attack has been mounted can be specifically determined. In addition, based on the examination results, limits can be imposed on the acceptance of connection requests, e.g., an inappropriate connection request can be rejected. 
   Moreover, in accordance with the method that reducing the weight, when a malisious user is mounting a malicious attack, the server  200  implementing communication control can identify this attack and maintain the server in a heavily loaded state and prevent its resources from being depleted. 
   According to the invention, provided are a communication control apparatus, a communication method and a communication control method that during communications for which IPv6 addresses are used, transmission source authorizations are examined and inappropriate connection requests are rejected, so that an attack from a malicious user to deplete resources is prevented. 
   Although the present invention has been shown and described with reference to specific embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.