JP2004297494A - Name resolution method and its apparatus in a plurality of network connection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an effective and efficient name resolution method when connecting a plurality of networks to users' terminals. <P>SOLUTION: The name solution apparatus 50 is installed between the terminal 1 and the plurality of the networks 10, 20. The name resolution apparatus 50 holds DNS caches 51, 52 for storing the result of the name resolution of a host name (a domain name) that is managed in each network for each of networks connected. When detecting a packet that requests the name resolution sent out of the terminal 1, the name solution apparatus 50 searches the domain name from the DNS cache according to priority of the network connected, and besides performs the name resolution for the DNS server of the network. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a name resolution method and device for realizing connection of a user terminal to a plurality of networks. Here, name resolution refers to obtaining an IP address (eg, “1.2.3.4”) corresponding to a domain name (eg, “www.aaa.co.jp”).
[0002]
[Prior art]
Generally, the conventional name resolution method realizes name resolution only for one connection network, and a terminal connected to one IP network sends a name resolution request packet to a name resolution server (DNS server), This is realized by the name resolution server sending the answer to the terminal as a name resolution response packet after the name resolution.
[0003]
However, on the day of the dead, construction of a high-speed content delivery network (hereinafter referred to as CDN) independent of the Internet has been promoted as a network for delivering large-volume content to users, and the existing connection with the Internet has been maintained. However, realization of simultaneous connection with a CDN has been demanded.
[0004]
As a conventional name resolution method capable of simultaneously connecting to a plurality of such networks, a resolver capable of asynchronously performing a name resolution request is implemented in a user terminal, and name resolution is performed for DNS servers of all connected networks. There is a method of transmitting a request packet and adopting the answer with the highest priority among the received answers (for example, see Non-Patent Document 1).
[0005]
On the other hand, as a conventional technique for efficiently performing name resolution, there is a DNS cache technique (for example, see Non-Patent Document 2). In this method, a DNS server has a DNS cache for temporarily storing a name resolution result, and stores a previously obtained name resolution result (IP address) for each domain name. The DNS server that has received the name resolution request answers the name resolution result if the DNS cache holds the name resolution result for the domain name of the name resolution request, and holds the name resolution result for the domain name. When there is no name resolution result, a name resolution result relating to the domain name is obtained from a server in the Internet and a response is made, and the newly obtained name resolution result is stored in the DNS cache. Generally, each name resolution result stored in the DNS cache has an expiration date, and in the prior art, the expired one is deleted from the DNS cache.
[0006]
[Non-patent document 1]
Moritomo Hirahashi, and one other "Study of name resolution method in independent multiple network connection", IEICE General Conference, September, 2002
[Non-patent document 2]
Odate Mitsumi Translated "DNS &BIND" (4th edition), O'Reilly Japan, February 2002, pp. 40-41
[0007]
[Problems to be solved by the invention]
In order to enable simultaneous connection to multiple networks, a mechanism for sending name resolution request packets to DNS servers of all connected networks and adopting the highest priority answer among the received answers In the method of performing name resolution by mounting the name on a user terminal, a very large number of settings for performing name resolution must be performed on each terminal, which increases the burden on the user.
[0008]
Further, there is a DNS cache technique as a conventional technique for efficiently performing name resolution, but originally, this technique does not consider name resolution in a plurality of network connections. Further, in the related art, when the expiration date of the name resolution result of each domain name stored in the DNS cache stored in the DNS server expires, the name resolution result of the domain name expires and is automatically deleted from the DNS cache. Therefore, when the terminal again requests the name resolution of the domain name, the DNS server needs to make another name resolution request to another DNS server. In other words, even if the terminal receives many name resolution requests for the domain name and the effect of the cache is very large, the name resolution result of the domain name is deleted from the DNS cache every time the expiration date expires. This leads to a decrease in user response.
[0009]
The present invention has been made to solve the above problems, and can avoid complicated settings of terminals and inefficient use of network devices, and provide effective and efficient name resolution in a plurality of network connections. It is an object of the present invention to provide a name resolution method and an apparatus for realizing the above.
It is another object of the present invention to provide a name resolution method and apparatus that enables a DNS cache to permanently retain a valid name resolution result for each domain name, thereby improving user response. I do.
Further, the present invention realizes that a domain name having many name resolution requests from a terminal and a domain name having a long elapsed time from the name resolution request is more likely to remain in the DNS cache, thereby constructing an effective DNS cache. It is an object of the present invention to provide a name resolution method and an apparatus for realizing the above.
[0010]
[Means for Solving the Problems]
According to the present invention, a name resolution device is installed between a user terminal (hereinafter, terminal) and a plurality of networks, and for every network to which the name resolution device is connected, the name of a host managed by each network (hereinafter, a name) , A domain name) is stored. Upon detecting the name resolution request sent from the terminal, the name resolution device searches the DNS cache for the domain name in accordance with the priority of the network, and performs the name resolution for the DNS server of all the connected networks. By implementing the method, effective and efficient name resolution is realized in a plurality of network connections. This can avoid complicated settings of the terminal and inefficient use of the name resolution device which is a network device.
[0011]
Further, in the present invention, before the expiration date of the name resolution result stored in the DNS cache expires, the name resolution device performs name resolution on the relevant domain name with respect to the relevant DNS server, and executes the relevant domain name in the DNS cache. Keep name resolution results up to date. As a result, it is possible to permanently retain a valid name resolution result for each domain name, thereby improving user response.
[0012]
On the other hand, when the above method is introduced, the number of domain names stored in the DNS cache keeps increasing, and when storing a new domain name, some means is used unless the amount of data that can be stored in the DNS cache is infinite. Must delete the data.
[0013]
According to the present invention, when the DNS cache has reached the maximum amount of data that can be stored in the DNS cache (hereinafter referred to as the maximum storage capacity), the name resolution device is configured to newly store a domain name that is not stored in the DNS cache. Deletes the corresponding data from the DNS cache based on a value obtained by weighting the number of inquiries from the terminal according to the elapsed time. As a result, a domain name having a larger number of name resolution requests from the terminal and a domain name having a shorter elapsed time from the name resolution request is more likely to remain in the DNS cache, thereby realizing an effective construction of a DNS cache table.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a basic configuration to which a name resolution method in a plurality of network connections of the present invention is applied. The terminal 1 is connected to the Internet 10, and the terminal 1 sends a name resolution request packet to the DNS server 11 of the Internet 10 for name resolution, and receives a name resolution response packet including the name resolution result. . Here, a name resolution device 30 is installed between the terminal 1 and a plurality of networks (the Internet 10 and the CDN 20 in FIG. 1) in order to realize name resolution in a plurality of network connections while avoiding complicated settings of the terminal. You. Upon detecting the name resolution request packet sent from the terminal 1 to the DNS server 11, the name resolution device 30 transmits a name resolution request packet and a name resolution response packet between the DNS server 11 of the Internet 10 and the DNS server 21 of the CDN 20. Sending and receiving, selecting an answer from the acquired answers according to the priority of the network, and notifying the terminal 1, the name resolution of the terminal 1 is completed.
[0015]
In other words, when the same domain name is used in a plurality of networks, the name resolution device 30 receives the name resolution results from the plurality of DNS servers. By setting, the terminal 1 can connect to the network with the highest priority. As a result, complicated settings in the terminal 1 can be avoided. In the setting of the priority, for example, when a CDN faster than the Internet is constructed, the priority of the CDN is made higher, so that even when the same domain name exists in both the CDN and the Internet, contents can be transferred from the faster CDN. You can get it.
[0016]
Here, as shown in FIG. 1, a method itself for realizing name resolution in a plurality of network connections by installing a name resolution device between a terminal and a plurality of networks has been previously proposed by the present inventors. (Japanese Patent Application 2002-194830). The problem with this is that the name resolution device, which is a network device, sends out a name resolution request packet to the DNS server of every network every time all name resolution requests received from the terminal, Since priority processing needs to be performed, name resolution is inefficient. The gist of the present invention is to avoid inefficient name resolution when a name resolution device is installed between a terminal and a plurality of networks.
[0017]
FIG. 2 is a configuration diagram showing one embodiment of a name resolution method in a plurality of network connections according to the present invention. As in FIG. 1, a name resolution device 50 is installed between a terminal and a plurality of networks (in FIG. 2, the Internet 10 and the CDN 20), and the name resolution device 50 includes a DNS cache ( In FIG. 2, an Internet DNS cache 51 and a CDN-DNS cache 52 are held. The name resolution device 50 performs name resolution in a plurality of network connections by searching its own DNS cache and performing name resolution with the DNS server of each network according to the priority of the network. This enables connection with a network.
[0018]
In the embodiment of FIG. 2, the terminal 1 connected only to the Internet 10 sends a name resolution request packet to the local DNS server 11 of the Internet 10. Upon detecting the name resolution request packet, if the priority of the CDN 20 is higher than that of the Internet 10, the name resolution device 50 first searches the CDN-DNS cache 52 for a domain name having the name resolution request, and searches the CDN-DNS cache 52 for the domain name. When the DNS cache 52 stores the name resolution result of the domain name, the DNS cache 52 sends the name resolution result of the domain name to the terminal 1, and completes the name resolution of the terminal 1. If the name is not stored, the name resolution device 50 makes a name resolution request to the DNS server 21, sends the name resolution result to the terminal 1, and associates the name resolution result in the CDN-DMS cache 52 with the domain name. Hold.
[0019]
When the name resolution device 50 obtains no response or an error from the DNS server 21, the name resolution device 50 determines that the domain name does not exist in the CDN 20, and then searches the Internet DNS cache 51 for the domain name. If the Internet DNS cache 51 stores the name resolution result of the domain name, the Internet DNS cache 51 sends the name resolution result of the domain name to the terminal 1, and the name resolution of the terminal 1 is completed. If the name is not stored, the name resolution device 50 makes a name resolution request to the DNS server 11, sends the name resolution result to the terminal 1, associates the name resolution result with the domain name in the Internet DNS cache 51, and stores the name resolution result. Hold. If no response or an error is obtained from the DNS server 11, the name resolution device 50 determines that neither the CDN 20 nor the Internet 10 has the domain name, and sends a name resolution error to the terminal 1.
[0020]
The name resolution device 50 pays attention only to the name resolution request packet and the name resolution response packet, and transfers all other packets according to the destination. The connection network is, of course, not limited to the configuration shown in FIG.
[0021]
FIG. 3 shows a configuration example of the CDN-DNS cache 52 held by the name resolution device 50. The configuration of the Internet DNS cache 51 is basically the same. The content stored in the CDN-DNS cache 52 is the CDN-DNS cache table 53, and the name resolution result (IP address) is stored for each domain name (Name). Each name resolution result stored in the CDN-DNS cache table 53 has a TTL indicating the expiration date of the name resolution result and a response acquisition time indicating the latest time at which the name resolution result was acquired / updated. are doing. For example, FIG. 3 shows that the expiration date of the name resolution result of the domain name “www.hoge.com” is “3600 seconds”, and the latest acquisition / update time is “11:01:00”. I have. Each name resolution result in the CDN-DNS cache table 53 further has a weighted search count, which is omitted in FIG.
[0022]
FIG. 4 shows an example of a method for effectively maintaining the DNS cache table (here, the CDN-DNS cache table 53) stored in the name resolution device 50. In one embodiment of the present invention, before the expiration date of the name resolution result expires and the name resolution result of the domain name stored in the DNS cache table is deleted, the name resolution for the domain name is performed, and the name resolution of the domain name is performed. It is intended to keep the latest name resolution result in the DNS cache table, and to effectively maintain the DNS cache table in name resolution.
[0023]
It is assumed that the contents of the CDN-DNS cache table 53 stored in the CDN-DNS cache 52 of the name resolution device 50 are as shown in FIG. 3, and the current time is "12:00:00". In this case, the expiration date of the name resolution result of the domain name “www.hoge.com” is 3600 seconds, and the previous answer acquisition time is 11:01:00, so the name resolution device 50 The name resolution result of “www.hoge.com” is acquired from the DNS server 21 of the CDN 20 within 3600 seconds from the acquisition time of the name resolution result, and the acquired name resolution result is reflected in the CDN-DNS cache table 53. Thus, the latest information on the domain name can be maintained.
[0024]
FIG. 5 is an example of a method of storing an effective domain name in a DNS cache table (here, the CDN-DNS cache table 53) stored by the name resolution device 50.
In the case of the embodiment in which the latest name resolution result is maintained as described with reference to FIG. 4, since the name resolution is performed before the expiration of the name resolution result, no domain name is deleted from the DNS cache table, and the name is stored once. The domain name requested to be resolved is permanently stored in the DNS cache table. In this case, for example, when the CDN-DNS cache table 53 shown in FIG. 3 reaches the maximum storage capacity, it becomes impossible to store a new domain name.
[0025]
Therefore, in another embodiment of the present invention, when storing a new domain name, a domain name with a small cache effect is deleted based on the number of weighted searches in the DNS cache table, and the new domain name is stored. A domain name with a small cache effect means a domain name with a small number of inquiries from terminals and a large number of cases with a long elapsed time since the inquiry, and the number of weighted searches indicates the cache effect quantitatively. I have.
[0026]
In the example of FIG. 5, an inquiry number is given each time a name resolution request is issued to the CDN-DNS cache 53, and the inquiry number is added to the number of weighted searches of the domain name. That is, if the current inquiry number is “100”, the inquiry number 101 is assigned to the next inquiry, the value of the inquiry is increased more than the old inquiry, and added to the number of weighted searches of the domain name. By repeating this, it can be said that the larger the value of the number of weighted searches is, the larger the domain name having a larger cache effect is.
[0027]
In FIG. 5, it is assumed that there is a name resolution request of “www.hoge.com” and then “www.hoge.net” from the terminal. In this case, in the name resolution request of “www.hoge.com”, since the current inquiry number of the CDN-DNS cache table 53 is “100”, the inquiry number “101” is added, and “www.hoge.com” is added. "Is added to the weighted search count of"", and the result becomes a CDN-DNS cache 53 '. Further, in the name resolution request of" www.hoge.net ", an inquiry number" 102 "is given, “102.” is added to the number of weighted searches of “www.hoge.net” to obtain a CDN-DNS cache 53 ″. That is, in the CDN-DNS cache 53, the number of weighted searches of “www.hoge.com” and “www.hoge.net” are the same, but in the CDN-DNS cache 53 ″, after the name resolution request is issued. "Www.hoge.net", which has a shorter elapsed time, has a larger value of the number of times of weighted search and is a domain name having a larger cache effect. Further, when the terminal requests to resolve “www.hoge2.com” that is not stored in the CDN-DNS cache 53 ″ from the terminal, and the CDN-DNS cache table 53 ″ has reached the maximum storage capacity. I do. In this case, “www.hoge1.com” having the smallest weighted search frequency and the smallest cache effect is searched, and after erasing it, “www” with the weighted search frequency “103” is added. .Hoge2.com "is added to the CDN-DNS cache table 53 '''.
[0028]
Although only the CDN-DNS cache 52 has been described so far, application to other DNS caches (for example, the Internet DNS cache 51) of the name resolution device 50 is also possible. Of the DNS cache table. In addition, the present embodiment can be applied to a DNS cache of a domain name whose name cannot be resolved. Note that the method of calculating the weighted search frequency is not limited to the above example.
[0029]
FIG. 6 is an overall processing flow diagram of the name resolution device 50. An example of the operation of the name resolution method using a multiple DNS cache of the present invention will be described with reference to FIG. When detecting the name resolution request packet transmitted from the terminal 1 to an arbitrary network (step 60), the name resolution device 50 checks the domain name for which the name resolution is requested (step 61). Next, the priority of the network is confirmed, the network having the highest priority is specified (step 62), and it is confirmed whether or not the DNS cache table of the network stores the name resolution result of the domain name (step 62). Step 63). If the DNS cache table stores the domain name, the name resolution result is sent to the terminal (step 66), and the name resolution of the terminal 1 is completed. If the DNS cache table does not store the domain name, a name resolution request is made to the DNS server of the network (step 64). When a response is returned to the name resolution request, the name resolution result is stored in the CDN-DNS cache table in association with the domain name (step 65), and the name resolution result is transmitted to the terminal 1. The name is transmitted (step 66), and the name resolution of the terminal 1 is completed. On the other hand, if the name cannot be resolved, the process returns to step 62, where the priority of the network is checked again, the network with the next highest priority is specified, and the same operation is repeated thereafter.
If the name cannot be finally resolved in the network with the lowest network priority, a name resolution error is sent to the terminal.
[0030]
FIG. 7 shows an operation example of maintaining the name resolution result stored in the DNS cache table at the latest information. The name resolution device 50 constantly checks the expiration dates of all the name resolution results stored in the DNS cache table (step 70). If there is a domain name whose remaining expiration date is equal to or less than a predetermined time, the DNS server of the network concerned , A name resolution request for the domain name is performed (step 71), the content of the obtained response is checked, and whether or not there is any change from the stored name resolution result is checked (step 72). If there is a change in the answer, the name resolution result in the DNS cache table is changed for all or only the updated answer (step 73). In step 70, if the remaining expiration dates of all the domain names are equal to or longer than a predetermined time, the operation ends, and if there is no change in the obtained answer in step 72, the operation ends.
[0031]
FIG. 8 shows an operation example of constructing a DNS cache table using the weighted search count. In step 63 of FIG. 6, it is confirmed whether or not the domain name is stored in the DNS cache table of the network. If the domain name is stored, the answer of name resolution is sent to the terminal in step 66. Next, a weighted search count is calculated from the number of name resolution requests for the DNS cache table from the terminal (step 80), and the calculated weighted search count is added to the weighted search count for the domain name in the DNS cache table. (Step 81). In step 63, it is confirmed whether or not the domain name is stored in the DNS cache table of the network. If the domain name is not stored, in step 64, a name resolution request is sent to the DNS server of the network. , Regardless of the presence or absence of a response, confirms the availability of the storage area of the DNS cache table of the network (step 82), and if there is a vacancy, stores the presence or absence of the response and the contents of the response (step 83). If there is no free space, the domain name with a small cache effect is deleted based on the weighted search count, and the presence or absence of the answer of the domain name and the content of the answer are stored (step 84).
[0032]
FIG. 9 is a functional block diagram of an embodiment of the name resolution device 50 for realizing name resolution using a plurality of DNS caches in a plurality of network connections according to the present invention. The name resolution device 50 includes a name resolution request detection function 90, a domain name confirmation function 91, and a name resolution function 92. The name resolution function 92 is related to the network priority storage function 93, the DNS cache function 94, the name resolution request function 95, and also to the name resolution response sending function 98. Further, the DNS cache function 94 is related to the latest information holding control function 96 and the weighted search count calculating function 97, and the name resolution request function 95 is related to the latest information holding control function 96. Note that the configuration in FIG. 9 is an example, and some functions may be embedded in another location.
[0033]
10 to 12 show examples of processing operations of the name resolution device 50 in the configuration example of FIG.
FIG. 10 is an example of the overall processing operation of name resolution using a plurality of DNS caches. The name resolution request detection function 90 detects the name resolution request packet sent from the terminal 1 ((1)), and the domain name check function 91 checks the domain name requested in the name resolution request packet. ([2]), the name resolution function 92 resolves the name of the domain name ([3]). In the name resolution, the name resolution function 92 checks the network with the highest priority from the network priority storage function 93 ((4)), and searches the DNS cache function 94 of the network for a name resolution result of the domain name. (▲ 5 ▼). Then, when the DNS cache function 94 of the network stores the name resolution result of the domain name, the name resolution function 92 passes the name resolution result to the name resolution response sending function 98 ((7)). If the DNS cache function 94 of the network does not store the name resolution result of the domain name, the name resolution function 92 passes the name resolution request to the name resolution request function 95 ([6]), and the name resolution request function 95 sends a name resolution request to the DNS server of the network, and if the name resolution result can be obtained, the name resolution function 92 passes the name resolution result to the name resolution response transmission function 98 ((7)). If name resolution cannot be obtained, the name resolution function 92 grasps the network with the next highest priority from the network priority storage function 93 ((8)), and the above operation is repeated. The name resolution response sending function 98 having received the name resolution result sends the name resolution result to the terminal 1.
[0034]
FIG. 11 is an example of a processing operation for maintaining the name resolution result stored in the DNS cache table at the latest information. The latest information holding control function 96 constantly monitors, from the DNS cache function 94 held for each network, a domain name for which the expiration date of the name resolution result is within a predetermined time, and temporarily detects the domain name upon detection. Is stored ((1)), and the domain name is passed to the name resolution requesting function 95 ((2)). The name resolution request function 95 sends a name resolution request to the DNS server of the network, receives the name resolution result, and passes the name resolution result to the latest information holding control function 96 ([3]). Upon receiving the name resolution result, the latest information holding control function 96 checks the difference between the temporarily stored name resolution result and the received name resolution result. Or, only the updated information updates the DNS cache function 94 of the network and deletes the temporarily stored name resolution result ([4]).
[0035]
FIG. 12 is an example of a processing operation for constructing a DNS cache table using the weighted search count. The name resolution function 92 searches the name resolution result of the domain name for which the name resolution request has been received from the DNS cache function 94 ((1)), and if the DNS cache function 94 stores the name, acquires it as the name resolution result. (▲ 2 ▼). Upon receiving the name resolution search, the DNS cache function 94 notifies the weighted search frequency calculation function 97 of each network that the search has been performed ([3]). The weighted search frequency calculation function 97 that has received the notification calculates the weighted search frequency and adds it to the weighted search frequency stored in the DNS cache function 94 ((4)). If the DNS cache function 94 does not store the domain name for which the name resolution request has been received, the name resolution request function 92 passes the name resolution request to the name resolution request function 95 ((5)), and the name resolution request The function 95 sends a name resolution request to the DNS server of the network, and passes the name resolution result to the name resolution request function 92 ([6]). The name resolution function 92 newly stores the received name resolution result in the DNS cache function 94 ((7)). When newly storing, if the DNS cache function 94 has reached the maximum storage capacity, the domain name with the smallest cache effect is deleted based on the number of weighted searches, and the name resolution result of the new domain name is deleted. Is stored.
[0036]
Note that some or all of the processing functions in the name resolution device shown in FIG. 9 are configured by a computer program, and the program can be executed using a computer to realize the present invention, or FIGS. Needless to say, the processing procedure shown in FIG. 8 can be configured by a computer program and the computer can execute the program. Further, a program for realizing the processing function by the computer or a program for causing the computer to execute the processing procedure is stored in a computer-readable recording medium such as an FD, an MO, a ROM, a memory card, and a CD. , A DVD, a removable disk, or the like, and can be stored or provided, and the program can be distributed through a network such as the Internet.
[0037]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the name resolution method and apparatus of this invention, it becomes possible to perform the effective and efficient name resolution method in several network connection, and can improve the user response of a communication service.
[Brief description of the drawings]
FIG. 1 is a configuration diagram to which a name resolution method in a plurality of network connections of the present invention is applied.
FIG. 2 is a configuration diagram of an embodiment for realizing a name resolution method using a plurality of DNS caches in a plurality of network connections according to the present invention.
FIG. 3 is an example of a DNS cache of a DNS server included in the name resolution device of the present invention.
FIG. 4 is an example of a method for effectively maintaining a DNS cache table according to the present invention.
FIG. 5 is an example of a method for storing an effective domain name in a DNS cache table according to the present invention.
FIG. 6 is an operation example of a name resolution method using a plurality of DNS caches according to the present invention.
FIG. 7 is an operation example of maintaining the name resolution result stored in the DNS cache table according to the present invention to the latest information.
FIG. 8 is an operation example of constructing a DNS cache table using a weighted search constant according to the present invention.
FIG. 9 is a functional block diagram relating to name resolution using a plurality of DNS caches in a plurality of network connections according to the present invention.
FIG. 10 is a processing operation example of name resolution using a multiple DNS cache according to the present invention.
FIG. 11 is an example of a processing operation for maintaining the name resolution result stored in the DNS cache table at the latest information according to the present invention.
FIG. 12 is an example of a processing operation of constructing a DNS cache table using the number of weighted searches according to the present invention.
[Explanation of symbols]
1 terminal
10 Internet
11 DNS server
20 Content Delivery Network (CDN)
21 DNS Server
50 Name resolution device
51 Internet DNS Cache
52 CDN-DNS cache

Claims (6)

A name resolution method for a plurality of network connections,
A name resolution device is installed between a user terminal (hereinafter, terminal) and a plurality of networks, and for each network to which the name resolution device is connected, the name of a host (hereinafter, domain name) managed by each network is set. Maintain a DNS cache that stores name resolution results,
When the name resolution device detects a packet requesting name resolution transmitted from the terminal (hereinafter, a name resolution request packet), the name resolution device uses the DNS cache according to the priority of the connected network. Performing a name resolution. The name resolution method according to claim 1,
The name resolution device checks the expiration date of the name resolution result for each domain name stored in the DNS cache, and performs the name resolution of the domain name to the DNS server of the network before the expiration date. Executing the DNS cache and updating all or a part of the name resolution result of the domain name in the DNS cache. The name resolution method according to claim 1 or 2,
The name resolution device measures the number of times the domain name of the DNS cache is searched, weights the measured number of searches according to the elapsed time, and performs the number of searches weighted according to the elapsed time ( A name resolution method comprising: searching for an arbitrary domain name from the DNS cache according to a weighted search count). A name resolution device that is installed between a terminal and a plurality of networks and performs name resolution in a plurality of network connections,
Means for detecting a name resolution request packet sent from the terminal;
A DNS cache for storing a name resolution result of a domain name managed in each network for each connected network;
Means for performing name resolution using the DNS cache according to the priority of the connected network;
A name resolution device comprising: The name resolution device according to claim 4,
Means for checking the expiration date of the name resolution result for each domain name stored in the DNS cache;
Means for performing name resolution of the domain name to the DNS server of the network before the expiration date of the name resolution result of the domain name is expired;
Means for updating all or part of the name resolution result of the domain name in the DNS cache after executing the name resolution;
A name resolution device comprising: The name resolution device according to claim 4 or 5,
Means for measuring the number of times the domain name of the DNS cache is searched;
Means for weighting the measured number of searches according to elapsed time,
Means for storing, for each domain name, the number of searches (weighted number of searches) weighted according to the elapsed time;
Means for searching an arbitrary domain name from the DNS cache table according to the weighted search count;
A name resolution device comprising:

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