JP2013219481A - Relay device, relay method, and relay program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable efficient communication to be performed in a path MTU value in which communication can be appropriately performed.SOLUTION: A network system includes a WAN and a LAN, and is configured so that a terminal at the WAN side and the terminal at the LAN side are communicably connected via a gateway relaying communication between the WAN and the LAN. The gateway: monitors a response time taken until a response to a data transmission from the terminal at the LAN side to the terminal at the WAN side is returned; determines whether a monitored response time is within a predetermined time; and notifies, when determined that the response is not within the predetermined time, the terminal at a local communication network side of a PMTU value that is data capacity transferrable once.

Description

  Embodiments described herein relate generally to a relay device, a relay method, and a relay program.

  In general, a network (IP network) using an Internet protocol is designed so that it can be constructed on various physical network media. Examples of the physical network medium include a cable and a radio. In order to make it possible to construct an IP network in a form that does not depend on a transmission method of a specific network medium, a physical network medium is transmitted from an upper IP layer through an interface abstracted by a concept called “link layer”. Modeled for use. The protocol model of the Internet protocol is expressed by a concept that a link layer is positioned in a lower layer and an IP layer is positioned on the link layer.

  In such an IP network, data is transmitted and received between nodes as a lump of data called an IP packet. When a predetermined node sends large data, the data is divided into a plurality of IP packets and transmitted / received as necessary. When an IP packet is transmitted and received between two nodes connected to an IP network on a predetermined network medium, the two nodes are connected by a conceptual “link”. In general, the maximum size of a data chunk that can be transmitted in one IP packet is determined for such a link. The maximum size of such data can be expressed as a communication protocol parameter used in the network medium (link layer). The maximum size of data that can be accepted by such a link is generally called an MTU (Maximum Transfer Unit) value.

  Incidentally, a plurality of IP networks are interconnected by routers. A router is a type of node that connects to a plurality of IP networks via links of various network media such as cables and radios and relays IP packets between the IP networks. A collection of IP networks interconnected by routers in this way is called the Internet.

  Here, consider a case where a node A connected to an IP network constructed on a predetermined network medium communicates with a node B connected to an IP network constructed on another network medium. For example, when two IP networks to which nodes A and B are connected are all connected to the same router, the router relays an IP packet transmitted from node A to node B. Can do. In addition, when there are a plurality of routers and a plurality of links connecting the plurality of routers between the IP network to which node A is connected and the IP network to which node B is connected, the route from node A to node B Each router existing above relays an IP packet, so that communication between the node A and the node B becomes possible.

  In the above example, MTU values related to the communication protocol used in each network medium are defined for a plurality of links on the route from node A to node B. Therefore, when an IP packet is transferred from node A to node B, the size of the IP packet is required not to exceed any of the MTU values of the links existing on the path from node A to node B. That is, when sending an IP packet to Node B, Node A is required to send an IP packet with a size equal to or smaller than the smallest MTU value in the entire link constituting the route from Node A to Node B. It is done. Such a minimum MTU value in all links on a predetermined route is called a “route MTU value” for the route.

  In the Internet protocol, a procedure for discovering a path MTU value to a predetermined destination node is standardly defined as path MTU discovery. Route MTU search in Internet protocol version 4 (IPv4) is defined in RFC (Request for Comments) 1191, and route MTU search in Internet protocol version 6 (IPv6) is defined in RFC 1981. RFC 1981 is derived from RFC 1191.

  The outline of the procedure in the IPv6 route MTU search will be described. An IP packet transmission source node assumes that an MTU value of a network medium (link) to which the node itself is connected is an initial route MTU value, and sends an IP packet. Send. This IP packet passes through a router and a link on the route before reaching the destination node. At this time, when the MTU value of a link in the middle of the route is smaller than the size of the IP packet, that is, when the data size of the IP packet exceeds the MTU value of the link, the router connected to the link And return a packet excessive message (Packet Too Big messages) to the source node. The format and communication procedure of such an excessive packet message are defined in RFC4443.

  The packet excessive message includes an MTU value that exceeds the size of the IP packet, and includes an MTU value of a link to which a router that transmits the message is connected. When the packet excessive message is transferred to the transmission source node, the transmission source node has a link in which an MTU value smaller than the initially assumed path MTU value is defined in the middle of the path to the destination node. Can be identified. Furthermore, the source node changes the size of the IP packet to the MTU value included in the packet excessive message and retransmits it, so that at least the next node to which the router that has returned the packet excessive message connects via the link IP packets can be reached. The source node can finally reach the destination node by repeating such processing.

  RFC 1981 states that nodes using IPv6 should implement path MTU discovery, but this is not a requirement. RFC 1981 describes that a node that does not implement path MTU search uses the minimum MTU value guaranteed to reach IPv6 as the path MTU value. On the other hand, in the IPv2 specification of RFC2460, a node using IPv6 is determined to have a minimum MTU value of 1280 octets. Therefore, a node that does not implement route MTU search always transmits an IP packet with the route MTU value set to 1280 octets.

  While the route MTU search procedure as described above exists, RFC4861 advertises the MTU value of the link to all nodes connected to the same link as the link to which the router itself is connected. The mechanism to do is described. RFC4861 is a standard related to the Neighbor Discovery Protocol of IPv6, where a certain node discovers other nodes connected to the same network medium (link), collects information related to the other nodes, and enables communication. The procedure for this is defined.

  In this RFC4861, the specification of a router advertisement message for a router to advertise information regarding the router's own existence and communication settings to nodes connected to the same link is defined for the neighbor discovery protocol. It is described that the MTU value of the link can be included as an option. The router can specify an MTU value recommended to be used by other nodes connected to the same link by using the MTU option. Therefore, when the MTU option of the router advertisement message is used, between the nodes connected to the same link, each node transmits an IP packet with the MTU value specified by the router without performing a route MTU search. It is possible.

  RFC 4861 describes a conceptual function that can be installed in an IPv6 node when the neighbor discovery protocol is implemented. Among these functions, there are a neighbor cache (Neighbor Cache) and a destination cache (Destination Cache) related to route MTU search. The neighborhood cache is a cache for temporarily storing information regarding other nodes connected to the link for each link to which a predetermined node is directly connected. The destination cache is a cache for temporarily storing information related to a destination node with which a predetermined node has recently communicated. RFC4861 describes that a path MTU value for each destination can be included in the destination cache.

  In addition, the route MTU value discovered using the route MTU search mechanism of RFC 1191 is cached for each destination node, and when communication to the same destination node occurs thereafter, the cache information is used to A technique for reaching an IP packet to a destination node without performing an MTU search is generally known.

JP 2007-180686 A JP-A-11-168492

J.Mogul et al, "Path MTU Discovery", Network Working Group, RFC1191, November 1990, [online], [searched November 7, 2011], Internet <http://tools.ietf.org/html/ rfc1191> J. McCann et al, "Path MTU Discovery for IP version 6", Network Working Group, RFC 1981, August 1996, [online], [searched November 7, 2011], Internet <http: //tools.ietf. org / html / rfc1981> S. Deering et al, "Internet Protocol, Version 6 (IPv6) Specification", Network Working Group, RFC2460, December 1998, [online], [searched November 7, 2011], Internet <http: // tools. ietf.org/html/rfc2460> A. Conta et al, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", Network Working Group, RFC4443, March 2006, [online], [searched November 7, 2011], Internet <http://tools.ietf.org/html/rfc4443> T.Narten et al, "Neighbor Discovery for IP version 6 (IPv6)", Network Working Group, RFC4861, September 2007, [online], [searched November 7, 2011], Internet <http: // tools. ietf.org/html/rfc4861>

  However, in the above-described prior art, each node may not be able to communicate using an appropriate route MTU value. Specifically, in the route MTU search, a packet excessive message returned by the router may not reach the transmission source node. For example, when the router does not have a route MTU search mechanism, or when a router on the way between the router and the transmission source node does not have a route MTU search mechanism, or because of a firewall, etc. In some cases, such as when an excessive message does not reach a router in the middle, the excessive packet message may not reach the source node. In such a case, since the transmission source node cannot acquire an appropriate route MTU value for the destination node, there is a problem that communication cannot be performed with the destination node using the appropriate route MTU value. Yes, it is called an MTU black hole problem, a pass MTU black hole problem, etc. (hereinafter, such a problem is referred to as a “black hole problem (or BH problem)”).

  As described above, in IPv6, in order to avoid communication failure due to excessive packets that cannot be detected by route MTU search, the source node uses 1280 octets, which is the minimum MTU value of IPv6, as the default route MTU value in advance. It is also possible. However, applying the default MTU value of 1280 octets as the default for all destination nodes is actually the size of an IP packet that is 1280 octets even for destination nodes whose path MTU value is greater than 1280 octets. Therefore, there is a problem that the communication efficiency is deteriorated.

  When the source node uses the above destination cache, an appropriate route MTU value can be selected for a destination node that has already been successfully communicated without using a route MTU search mechanism. It may be possible. However, even in the conventional technology using the destination cache, each node uses the path MTU search until the communication is successful, so that each node is not appropriate because the packet excessive message does not reach the transmission source node. The problem that communication cannot be performed with the destination node using the path MTU (or Path MTU, PMTU) value cannot be solved.

  In addition, before the LAN side relay device that has received communication from the transmission source device communicates with the destination device, the LAN device attempts to perform prior confirmation communication with the destination device, confirms an appropriate PMTU, and sends the PMTU to the transmission source terminal. There is a technology to communicate with the value of. However, a process for confirming an appropriate PMTU for each destination is required, and the prior confirmation communication is repeated while changing the transmission data size. Therefore, it takes a considerable time to identify an appropriate PMTU, resulting in poor communication efficiency. Problem arises.

  Further, a technique for exchanging path information between routers on the Internet and exchanging PMTU information up to a destination device that can be a destination known by the router and notifying the transmission source device of the optimal PMTU up to the destination device There is. However, there is a problem that only the communication with a predetermined destination device that has been notified can be dealt with, and the configuration of each router on the existing Internet must be modified.

  The technology disclosed in the present application has been made in view of the above, and provides a relay device, a relay method, and a relay program capable of efficiently performing communication with a route MTU value capable of appropriately performing communication. The purpose is to do.

  The relay device according to the embodiment is a relay device that relays communication between a wide area communication network and a local communication network, and is a response to data transmission from a terminal on the local communication network side to a terminal on the wide area network side A monitoring unit that monitors a response, a determination unit that determines whether a response is returned within a predetermined time based on monitoring by the monitoring unit, and a determination that the response is not received within a predetermined time by the determination unit Generates a message indicating a pre-stored data capacity that can be transferred at one time and is a data capacity that is smaller than the data capacity at the time of data transmission, and sends the message to the local communication network side And a notification unit for notifying the terminal.

  The relay device, the relay method, and the relay program according to the embodiment have an effect that communication can be efficiently performed with a path MTU value that allows appropriate communication.

FIG. 1 is a diagram illustrating a configuration example of a network system according to the first embodiment. FIG. 2 is a diagram illustrating a configuration example of the gateway according to the first embodiment. FIG. 3 is a diagram illustrating an example of data stored in the storage unit according to the first embodiment. FIG. 4 is a diagram illustrating an example of data stored in the storage unit according to the first embodiment. FIG. 5 is a diagram illustrating an example of data stored in the storage unit according to the first embodiment. FIG. 6 is a sequence diagram illustrating a processing procedure performed by the network system according to the first embodiment. FIG. 7 is a flowchart showing a processing procedure by the gateway according to the first embodiment. FIG. 8 is a flowchart showing a processing procedure by the gateway according to the first embodiment. FIG. 9 is a diagram illustrating a configuration example of a gateway according to the second embodiment. FIG. 10 is a diagram illustrating an example of data stored in the storage unit according to the second embodiment. FIG. 11 is a diagram illustrating an example of data stored in the storage unit according to the second embodiment. FIG. 12 is a sequence diagram illustrating a processing procedure performed by the network system according to the second embodiment. FIG. 13 is a flowchart showing a processing procedure by the gateway according to the second embodiment. FIG. 14 is a sequence diagram illustrating a processing procedure performed by the network system according to the third embodiment. FIG. 15 is a flowchart showing a processing procedure by the gateway according to the third embodiment. FIG. 16 is a flowchart showing a processing procedure by another gateway. FIG. 17 is a diagram illustrating a computer that executes a relay program.

  Embodiments of a relay device, a relay method, and a relay program according to the present application will be described below in detail with reference to the drawings. Note that the relay device, the relay method, and the relay program according to the present application are not limited to the embodiment.

[Configuration of network system according to first embodiment]
First, the network system according to the first embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration example of a network system according to the first embodiment.

  As illustrated in FIG. 1, a network system 100 according to the first embodiment includes a LAN (Local Area Network) 40 including terminals 20 </ b> A and 20 </ b> B and a WAN (Wide Area Network) including terminals 20 </ b> C and a router 30. ) 50, and the gateway 10 that relays communication exists between the LAN 40 and the WAN 50. In the following description, IPv6 communication over Ethernet (registered trademark) is assumed, but the present invention is not limited to this. The layer 3 may be IPv4, for example, and the layer 2 is not limited to Ethernet.

  The gateway 10 is a home gateway or the like provided in a home connected to the LAN 40 and the WAN 50 so that the LAN-side terminals 20A and 20B can communicate with the WAN-side terminal 30. The gateway 10 is a relay device that relays IP packets transmitted by the LAN side terminals 20A and 20B.

  The LAN side terminals 20A and 20B are connected to the gateway 10 and perform IPv6 communication with the terminal 20C on the Internet via the gateway 10 or accessible via the Internet. The router 30 is a relay device that relays IP packets transmitted by the gateway 10 and the terminal 20C. Although FIG. 1 illustrates three terminals, one router, and one gateway, the network system 100 includes two or less terminals, four or more terminals, and two or more routers. And gateways may be included. Further, the connection relationship between the terminal, the router, and the gateway is not limited to the example shown in FIG.

[Gateway Configuration]
Next, the configuration of the gateway 10 shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a diagram illustrating a configuration example of the gateway according to the first embodiment. As shown in FIG. 2, the gateway 10 includes a communication unit 11, a communication unit 12, a storage unit 13, a communication monitoring unit 14, a PMTU notification determination unit 15, and a PMTU notification unit 16, and includes a LAN-side terminal 20A. Connected. The processing of each of these units will be described below.

  The communication unit 11 and the communication unit 12 control communication related to various information exchanged between a connected terminal and a router. For example, the communication unit 11 receives an IP packet from the LAN side terminal 20A to the WAN side terminal 20C, and transmits a PMTU value to the LAN side terminal 20A. Further, for example, the communication unit 12 transmits an IP packet from the LAN-side terminal 20A to the WAN-side terminal 20C.

  The storage unit 13 stores data and programs necessary for various types of processing. Particularly closely related to the present invention are a monitoring time (FIG. 3) used by the communication monitoring unit 14 described later, and a PMTU notification described later. The unit 16 stores the value of the PMTU notified to the LAN side terminal 20A (FIG. 4), information on the address of the LAN side terminal (FIG. 5), and the like.

  For example, as illustrated in FIG. 3, the storage unit 13 stores “60” seconds as the monitoring time used by the communication monitoring unit 14. The monitoring time is set as “60” seconds common to all communication protocols, but may be set for each communication protocol or may be set for each set of communication protocol and port number. In accordance with the set monitoring time, the communication monitoring unit 14 confirms the contents of the packet and specifies the monitoring time for waiting for a response. The monitoring time described above is preferably shorter than the timeout time of the communicating application.

  Further, as illustrated in FIG. 4, the storage unit 13 stores the LAN side terminal PMTU value “1280” bytes as the value of the PMTU that the PMTU notification unit 16 notifies to the LAN side terminal 20 </ b> A. The LAN side terminal PMTU value is desirably the lowest value guaranteed by standard specifications (1280 bytes in the case of IPv6 over Ethernet). The LAN side terminal PMTU value may be stored for each destination, for each destination address range, and for all WAN side destinations.

  In addition, as illustrated in FIG. 5, the storage unit 13 stores the MAC address “AA: BB: CC: DD: EE: FF” of the device “terminal A” on the LAN side as information on the address of the terminal on the LAN side. The IP address “fe80 :: 1001” (or global unicast address) is stored in association with each other. The storage unit 13 stores a private address band that can be assigned to the LAN side for IPv4, an assigned address, and the like, and stores a prefix, a unicast address, and the like assigned to the LAN side for IPv6.

  The communication monitoring unit 14 monitors the response time when a response to the packet transmission from the LAN side terminal 20A to the WAN side terminal 20C is returned. Specifically, the communication monitoring unit 14 does not monitor communication within the LAN, only monitors communication from the LAN side to the WAN side, and packet transmission is started from which LAN side address to which WAN side address. And temporarily storing the measured time from the time when the start of communication is detected. Then, when there is a response from the destination within the monitoring time (see FIG. 3) stored in the storage unit 13, the communication monitoring unit 14 removes the measurement time from the monitoring target, that is, deletes the measurement time from the temporary storage. Note that an error message or the like from a communication device in the middle of the WAN side route is also a problem different from the black hole problem, and may be excluded from the monitoring target.

  The PMTU notification determination unit 15 determines whether a response is received within a predetermined time by the communication monitoring unit 14. Specifically, the PMTU notification determination unit 15 requires communication that does not respond even after the monitoring time elapses as a result of the monitoring by the communication monitoring unit 14, that is, the PMTU value of the LAN side terminal 20A is reset. It is determined that the setting process is necessary.

  Based on the determination result of the PMTU notification determination unit, the PMTU notification unit 16 notifies the source terminal 20A that has started communication to the WAN side of the PMTU value stored in the storage unit 13. For example, the PMTU notification unit 16 generates a response by packet overo (packet too big) message of ICMPv6 (Internet Control Message Protocol for IPv6) message for packet transmission from the LAN side terminal to the WAN side terminal. A PMTU value may be included.

  In this packet excessive message, the minimum PMTU value (for example, 1280 bytes) is specified for the destination. Furthermore, notification may be made so that the minimum PMTU is set for all WAN-side destinations. In addition, the notification destination may be not only the source terminal that has started communication to the WAN side, but all terminals on the LAN side, and the PMTU value is notified to each terminal by a message in which a new option is defined by an RA (Router Advertisement) message. May be. In addition, the opportunity, conditions, etc. to notify shall be memorize | stored in the memory | storage part 13. FIG.

  As illustrated in FIG. 2, the terminal 20 </ b> A includes a communication unit 21 and a PMTU setting unit 22. The communication unit 21 controls communication related to various information exchanged with the connected gateway 10 or the like. For example, the communication unit 21 receives a packet excessive message in which the PMTU value is set from the gateway 10.

  Based on the PMTU value received from the gateway 10, the PMTU setting unit 22 sets the packet to be transmitted to the WAN side terminal 10C in units of the PMTU. Specifically, the value of PMTU is extracted from the packet excessive message received from the gateway 10 and the predetermined address (original destination, etc.) or address range (all destinations other than the LAN side, that is, the WAN side, etc.) A predetermined PMTU value is set.

[Processing procedure by network system]
Next, the flow of processing by the network system 100 according to the first embodiment will be described with reference to FIG. FIG. 6 is a sequence diagram illustrating a processing procedure performed by the network system 100 according to the first embodiment. In FIG. 6, the network system 100 includes a gateway 10, LAN-side terminals 20 </ b> A and 20 </ b> B, a WAN-side terminal 20 </ b> C, and a router 30. In FIG. 6, it is assumed that the black hole problem is caused by the router 30 (black hole router).

  In the example of FIG. 6, the gateway 10 stores in advance the link MTU value of the LAN side interface of the gateway 10 connected to the terminal 20A for the MTU of the LAN side network. Advertisement) MTU option is used to notify the LAN side terminal 20A as a link MTU. Note that the RA may be notified when an RS (Router Solicitation) is received from the terminal. Alternatively, the terminal 20A may set the link MTU itself.

  Then, the terminal 20A sets the value of the link MTU as the link MTU of the communication interface of the own terminal. In addition, when the default link MTU between the LAN side terminals is adjusted, the process for setting the link MTU is not necessary.

  Thereafter, the terminal 20A starts communication with the WAN-side terminal 20C using the set link MTU. Then, the gateway 10 monitors communication while relaying the packet between the terminal 20A and the terminal 20C, and confirms communication of the packet. Specifically, the gateway 10 detects the start of communication from the LAN side to the WAN side, temporarily stores a pair of source and destination addresses, and monitors whether a response is received from the destination within the monitoring time. To do. As a result, when a response is received within the monitoring time, the temporarily stored information is deleted.

  On the other hand, if the gateway 10 does not receive a response within the monitoring time, the gateway 10 determines that the destination is unreachable, that is, has encountered a black hole problem, and stores the LAN side terminal PMTU value stored in advance (example in FIG. 4). Then, 1280 bytes) is notified to the terminal 20A on the LAN side. For example, the gateway 10 generates an ICMPv6 type = 2 packet oversize message defined in RFC4443 and transmits it to the terminal 20A. Then, the terminal 20A that has received the notification sets the value notified as the PMTU for the destination and communicates with the terminal 20C again.

[Processing procedure by gateway]
Next, a processing procedure by the gateway 10 according to the first embodiment will be described with reference to FIGS. 7 and 8. 7 and 8 are flowcharts showing a processing procedure by the gateway according to the first embodiment.

  As shown in FIG. 7, when the communication unit 11 of the gateway 10 receives a packet from a terminal on the LAN side (step S101), the communication unit 11 determines whether the destination is a terminal on the WAN side (step S102). For example, the communication unit 11 refers to the information on the address of the LAN side terminal stored in the storage unit 13 (see FIG. 5), and determines whether the destination address corresponds to the address of the LAN side terminal. Then, it is determined whether or not the destination is a WAN side terminal. This determination may be a complete match determination or a partial match determination. Alternatively, when the gateway 10 has a switch function, the determination may be made based on the destination MAC address.

  As a result, if the destination is not a WAN-side terminal (No at Step S102), that is, if it is determined that the destination is a terminal in the LAN, the communication unit 11 transfers the packet to the destination as it is (Step S103). The process ends. When the destination is a WAN terminal (Yes at Step S102), the packet is transferred to the destination of the WAN terminal (Step S104), and the PMTU notification determination unit 15 determines whether or not a black hole problem has been encountered. The determination process (detailed later using FIG. 8) is executed (step S105).

  As a result, when the PMTU notification determination unit 15 determines that the black hole problem has not been encountered (No at Step S105), the process is ended as it is. When the PMTU notification determination unit 15 determines that the black hole problem has been encountered (Yes at Step S105), the PMTU stored in advance is notified to the transmission source terminal (Step S106), and the process ends. Thereafter, the transmission source terminal that has received the notification sets the value notified as the PMTU for the destination and communicates with the transmission destination terminal again.

  Next, the determination process in step S105 will be described in detail with reference to FIG. As illustrated in FIG. 8, the communication monitoring unit 14 of the gateway 10 temporarily stores a pair of a source address and a destination address (step S201). Then, the PMTU notification determination unit 15 determines whether there is a response from the destination to the transmission source within the monitoring time (for example, 60 seconds) (step S202).

  As a result, when the PMTU notification determination unit 15 determines that there is a response from the destination to the transmission source within the monitoring time (Yes in step S202), it is determined that the black hole problem has not been encountered and the communication monitoring is performed. The unit 14 deletes the temporary storage of the combination of the source and destination addresses (step S203) and ends the process. If the PMTU notification determination unit 15 determines that there is no response from the destination to the transmission source within the monitoring time (No at Step S202), the PMTU notification determination unit 15 determines that there is a black hole problem (Step S204) and ends the process. To do.

[Effect of the first embodiment]
As described above, the gateway 10 monitors the response time when a response to the packet transmission from the LAN side terminal 20A to the WAN side terminal 20C is returned, and whether the monitored response time is within a predetermined time. If it is determined that the response is not within the predetermined time, the value of PMTU, which is a data capacity that can be transferred at one time, is notified to the LAN side terminal 20A. Then, the LAN-side terminal 10A is configured to transmit a packet to the WAN-side terminal 20C using the PMTU based on the PMTU value received from the gateway 10. Thereby, although communication efficiency may be inferior compared with communication by optimal PMTU, a black hole problem can be avoided without putting a hand in the WAN side communication apparatus. In addition, the delay can be reduced until the communication with the destination apparatus is actually started in that the appropriate PMTU of the route to the destination is not investigated in advance for all the communications. As a result, it is possible to efficiently perform communication with the value of the MTU that allows appropriate communication.

  Further, according to the first embodiment, when communication is performed between the terminal 20A and the terminal 20B in the LAN, the WAN side is maintained while maintaining a state where communication can be performed with the value of the link MTU of the communication interface. When communicating with other terminals, it is possible to communicate with an MTU value that avoids the black hole problem.

  Further, according to the first embodiment, when a packet for prohibiting fragment processing is set in a packet when communicating by IPv4, it is effective as in the case of IPv6 communication. When fragmentation is not prohibited in IPv4, each router on the route performs fragment processing as appropriate when the communication MTU is excessive, but depending on the firewall, etc., it is set not to receive fragmented packets. Sometimes. In other cases, the fragment processing also affects the communication efficiency because the load on the router increases. According to the present invention, it may be effective even in IPv4 communication.

  In addition, according to the first embodiment, when an Ethernet jumbo frame is applied to a communication interface of a communication device including a terminal in a LAN, depending on the specification of the jumbo frame, for example, 8000 to 150,000 bytes. It is possible to communicate with a frame size of about (Ethernet MTU is 1500 bytes). In this case, the value of MTU is large and the communication efficiency is improved.

(Second embodiment)
By the way, in the first embodiment described above, when it is determined whether there is no response from the destination to the transmission source within the monitoring time, and it is determined that there is no response, it is determined that the black hole problem has been encountered. However, the present invention is not limited to this, and processing for confirming that communication cannot be performed due to the value of the PMTU may be performed.

  Therefore, in the following second embodiment, in order to confirm that communication cannot be performed due to the value of the PMTU, if there is no response within the monitoring time, the same destination has a small size (for example, the minimum of the PMTU). Value) is transmitted, and it is determined whether or not there is a response within a predetermined time. If there is a response within the predetermined time, it is determined that a black hole problem has been encountered. Hereinafter, the configuration and processing of the gateway 10A according to the second embodiment will be described with reference to FIGS. In the following description, the description of the configuration and processing common to the first embodiment is omitted.

  As shown in FIG. 10, the gateway 10A according to the second embodiment is different from the gateway 10 according to the first embodiment shown in FIG. Further, the storage unit 13 of the gateway 10A stores the communication confirmation time used by the communication confirmation unit 17 and the size of the packet used when the communication confirmation unit 17 uses the communication confirmation, as shown in FIG. This is different from the gateway 10 according to the embodiment.

  For example, as illustrated in FIG. 10, the storage unit 13 stores “4” seconds as the communication confirmation time used by the communication confirmation unit 17. The communication confirmation time used by the communication confirmation unit 17 may be a short time used in ICMPv6 Ping or the like.

  Further, as illustrated in FIG. 11, the storage unit 13 stores “1280” bytes as the size of the packet at the time of the communication confirmation used by the communication confirmation unit 17. Note that the size of the packet used for the communication confirmation used by the communication confirmation unit 17 is preferably the same as the value of the PMTU notified by the PMTU notification unit 16 to the terminal 20A on the LAN side.

  The communication confirmation unit 17, when the PMTU notification determination unit 15 determines that the response is not within a predetermined time, the packet having a size smaller than that when the packet is transmitted from the LAN side terminal 20 </ b> A to the WAN side terminal 20 </ b> C. Is transmitted to the WAN-side terminal 20C, and it is confirmed whether or not there is a response to the transmission within the communication confirmation time. The communication confirming unit 17 may be, for example, the size of the PMTU scheduled to be notified to the terminal 20A as a small-sized packet to be transmitted for communication confirmation, or the minimum MTU guaranteed for a smaller size, for example, Ethernet. It may be a value.

  That is, in the first embodiment, it is determined that the black hole problem has been encountered because there is no response from the destination within a predetermined time for the communication from the terminal 20A. For example, the destination terminal is down. For example, communication may not be possible due to reasons other than the black hole problem. Therefore, in the second embodiment, the communication confirmation unit 17 further confirms communication by transmitting a small-sized packet in order to confirm that communication is not achieved due to the value of the PMTU used for communication. . Thereby, it is possible to appropriately determine whether or not a response is not returned due to the black hole problem.

  Next, the flow of processing by the network system according to the second embodiment will be described with reference to FIG. FIG. 12 is a sequence diagram illustrating a processing procedure performed by the network system according to the second embodiment. As illustrated in FIG. 12, the terminal 20A starts communication with the WAN-side terminal 20C using the link MTU. Then, the gateway 10 monitors communication while relaying the packet between the terminal 20A and the terminal 20C, and confirms communication of the packet.

  If there is no response within a predetermined time as a result of the communication monitoring, the gateway 10 communicates with the same destination using a small packet (such as ICMPv6 ping for IPv6) and within the communication confirmation time ( For example, the time calculated by round trip time of communication with the WAN may be used as appropriate, or the time calculated by performing statistical processing or the like may be used. Therefore, it is determined that processing is necessary.

  On the other hand, when there is no response, it is due to another cause, so the PMTU is not notified to terminal 20A. In this case, a message indicating that the communication is interrupted due to another cause may be notified to the terminal 20A instead. This communication confirmation is not intended to identify the optimal PMTU, but is to confirm that the IP packet can reach the destination, and can confirm the presence or absence of a response in a short time.

  If the gateway 10 determines that it is due to the black hole problem, the gateway 10 notifies the LAN side terminal 20A of the LAN side terminal PMTU value (1280 bytes in the example of FIG. 4) stored in advance. The terminal 20A that has received the notification sets the value notified as the PMTU for the destination.

  Next, the procedure of the determination process performed by the gateway 10A according to the second embodiment will be described with reference to FIG. FIG. 13 is a flowchart showing a processing procedure by the gateway according to the second embodiment.

  As shown in FIG. 13, the communication monitoring unit 14 of the gateway 10A temporarily stores a pair of a source address and a destination address (step S301). Then, the PMTU notification determination unit 15 determines whether there is a response from the destination to the transmission source within the monitoring time (for example, 60 seconds) (step S302).

  As a result, when the PMTU notification determination unit 15 determines that there is a response from the destination to the transmission source within the monitoring time (Yes in step S302), it is determined that the black hole problem has not been encountered and the communication monitoring is performed. The unit 14 deletes the temporary storage of the combination of the source and destination addresses (step S303) and ends the process.

  Also, if the PMTU notification determination unit 15 determines that there is no response from the destination to the transmission source within the monitoring time (No in step S302), the communication confirmation unit 17 sends a smaller value to the destination WAN terminal. Size packet transmission (ICMPv6 ping or the like if IPv6) is performed (step S304), and it is determined whether or not there is a response within a predetermined time (step S305).

  As a result, when it is determined that there is no response within the predetermined time (No at Step S305), the communication confirmation unit 17 determines that the problem is different from the black hole problem (Step S306), and ends the process. To do. If the communication confirmation unit 17 determines that there is a response within a predetermined time (Yes at Step S305), the communication confirmation unit 17 determines that there is a black hole problem (Step S307) and ends the process.

  As described above, according to the second embodiment, when it is determined that the response is not within the predetermined time for monitoring, the gateway 10A transmits a packet from the LAN side terminal to the WAN side terminal. A packet having a data capacity smaller than the time is transmitted to the terminal on the WAN side, and it is confirmed whether or not a response to the transmission is within a predetermined time. Then, when it is confirmed that the response is within a predetermined time for confirmation of communication, the gateway 10A notifies the terminal on the LAN side of the value of the PMTU. For this reason, it is possible to appropriately determine whether or not a response is not returned due to the black hole problem.

(Third embodiment)
By the way, in the present invention, the gateway may store the destination information in the WAN side terminal and the PMTU used for data communication with the WAN side terminal in association with each other.

  Therefore, in the following description of the third embodiment, the gateway manages a set of addresses or address ranges of the destination on the WAN side (may be a range indicating the entire address on the WAN side) and a PMTU applied to the destination. A case where the management table is stored will be described. Hereinafter, the processing of the gateway according to the third embodiment will be described with reference to FIGS.

  First, the flow of processing by the network system according to the third embodiment will be described with reference to FIG. FIG. 14 is a sequence diagram illustrating a processing procedure performed by the network system according to the third embodiment. As illustrated in FIG. 14, the gateway 10 stores a management table in which a destination address is associated with a PMTU applied to the destination. In the example of FIG. 14, it is assumed that the management table is in an initial state in which nothing is stored yet before the process is started.

  As illustrated in FIG. 14, the terminal 20A starts communication with the WAN-side terminal 20C using a link MTU (for example, 1500 bytes). When receiving the communication from the LAN side terminal to the WAN side terminal, the gateway 10 specifies the destination and MTU of the packet of the communication and collates with the destination in the management table. This collation may be a perfect match or a partial match.

  If there is no corresponding destination as a result of the collation, the gateway 10 directly transfers the packet to the WAN side terminal. On the other hand, as a result of the collation, if the destination is a corresponding destination, the gateway 10 does not forward the packet to the destination if the MTU of the packet is larger (or different) than the value of the PMTU stored in association with the destination. In addition, an ICMPv6 message is generated using the PMTU information corresponding to the destination in the management table and returned to the transmission source terminal. This message is the same as the specification of the ICMPv6 packet excessive message received by the transmission source terminal when the normal PMTU search functions, and is usually a message including an appropriate PMTU value. Since the present invention takes into consideration that this PMTU search does not work and this message is not returned, the value of the PMTU included in this message generated by the gateway 10 corresponds to the corresponding destination in the management table. The value of PMTU to be embedded is embedded.

  In the example of FIG. 14, since the management table is in an initial state in which nothing is stored yet, the gateway 10 assumes that there is no corresponding destination as a result of collation, and transfers the packet to the WAN side terminal 20C as it is. The communication is monitored while relaying the packet between the terminal 20A and the terminal 20C, and the communication of the packet is confirmed.

  Then, the gateway 10 performs data communication of a small packet to the same destination when there is no response within a predetermined time as a result of the communication monitoring, and when there is a response from the destination within the communication confirmation time, the gateway 10 It is determined that this is due to a hole problem, and the PMTU is notified to the terminal 20A and reflected in the management table. In other words, the gateway 10 associates the destination of the terminal C with the PMTU value that is guaranteed to arrive (for example, the value of the PMTU when the terminal 20C is reached in the communication confirmation), and stores it in the storage unit 13.

  Thereafter, the terminal 20A that has received the notification sets the value notified as the PMTU for the destination, and transmits the value again to the WAN-side terminal 20C with the set PMTU value.

  Next, a processing procedure by the gateway according to the third embodiment will be described with reference to FIG. FIG. 15 is a flowchart showing a processing procedure by the gateway according to the third embodiment.

  As shown in FIG. 15, when the communication unit 11 of the gateway 10 receives a packet from a terminal on the LAN side (step S401), the communication unit 11 determines whether the destination is a terminal on the WAN side (step S402).

  As a result, when the destination is not the WAN side terminal (No at Step S402), that is, when it is determined that the destination is a terminal in the LAN, the communication unit 11 directly transfers the packet to the destination (Step S403). The process ends. If the destination is a WAN-side terminal (Yes at Step S402), the communication monitoring unit 14 checks whether there is a packet destination corresponding to the destination information in the management table (Step S404).

  As a result, when the packet received from the LAN side terminal is a packet corresponding to the destination information stored in the management table (Yes at step S405), the communication monitoring unit 14 stores the packet in association with the destination information. It is determined whether the packet is equal to or less than the PMTU (step S409). As a result, when the communication monitoring unit 14 determines that the packet is equal to or less than the PMTU (Yes at Step S409), the communication unit 12 transfers the packet to the WAN side terminal (Step S410) and ends the process. . If the communication monitoring unit 14 determines that the packet is not equal to or less than the PMTU (No at Step S409), the PMTU stored in advance is notified to the transmission source terminal (Step S411), and the process ends.

  Returning to the description of step S405, the communication monitoring unit 14 determines that the packet received from the terminal on the LAN side is not a packet corresponding to the destination information stored in the management table (No in step S405). The packet is transferred to the destination of the terminal (step S406), and the PMTU notification determination unit 15 executes a determination process (for example, the determination process of FIGS. 8 and 13 described above) for determining whether or not a black hole problem has been encountered. (Step S407).

  As a result, if the PMTU notification determination unit 15 determines that the black hole problem has not been encountered (No at step S407), the process ends. Alternatively, this is notified to the transmission source terminal. If the PMTU notification determination unit 15 determines that a black hole problem has been encountered (Yes at step S407), the destination is added to the management table and stored together with the PMTU (step S408), and stored in advance. Is notified to the transmission source terminal (that is, the PMTU stored in association with the destination) (step S411), and the process ends. Thereafter, the transmission source terminal that has received the notification sets the value notified as the PMTU for the destination and communicates with the transmission destination terminal again.

  That is, the gateway 10 associates the WAN-side destination with the reachable PMTU and stores it in the management table, so that even if the LAN-side terminal does not store the PMTU up to the destination, In one round-trip communication, a PMTU that can reach the destination can be acquired by receiving a packet excessive message generated by the gateway, and the PMTU can communicate with the destination.

  As described above, according to the third embodiment, the gateway 10 stores the destination information in the WAN-side terminal and the PMTU value when performing data communication with the WAN-side terminal in association with each other. Then, when data communication from the LAN side terminal to the WAN side terminal is performed, when the destination information corresponding to the destination information of the WAN side terminal is stored in the storage unit, the gateway It is monitored whether or not the PMTU value in data communication is larger than the PMTU value stored in association with the destination information. If the PMTU value in the data communication is larger than the PMTU value stored in association with the destination information, the data communication to the terminal on the WAN side is stopped, that is, the gateway 10 is the WAN that is the communication destination. The PMTU value stored in association with the destination information is notified to the LAN side terminal by a packet excessive message or the like without being transferred to the side terminal. In other words, the gateway 10 stores the PMTU value obtained by experience of communication with the WAN side by a predetermined terminal on the LAN side in the management table, and is stored in the management table in another terminal that first sends a packet to the destination. PMTU values can be applied. For this reason, it becomes possible to perform communication more efficiently with the PMTU value that allows appropriate communication using the PMTU value stored in the management table. As described above, the management table information may be shared by all the terminals on the LAN side, or the management table may be held for each terminal. In addition, when the same PMTU value is applied to all destinations on the WAN side, it is not essential to store the destination information and the PMTU value in association with each other in the management table, and the destination information and the PMTU value to be applied are separated. May be managed.

  Further, according to the present invention, when the number of times that the black hole problem has occurred for different destinations within a predetermined time becomes equal to or greater than the predetermined number, for all terminals on the WAN side, a predetermined value (for example, the minimum MTU) (Value) may be set in the management table.

  Such a process will be described with reference to FIG. 16 for a determination process performed by the gateway. As shown in FIG. 16, the determination process by the gateway is determined to be a black hole problem within a predetermined time after being determined as a black hole problem as compared with the determination process illustrated in FIG. 13 (step S <b> 507). A process (step S508) for determining whether or not the number of times has exceeded the threshold is newly added.

  As a result of this processing, when the number of times that the black hole problem is determined exceeds the threshold, the management table is set to take a predetermined value (for example, the minimum MTU value) as the PMTU value for all the WAN side terminals (for example, Step S509).

  That is, the fact that the black hole problem has occurred several times for different destinations within a certain period of time means that there is a problem in the route immediately outside the gateway 10, and that the connection destination of the gateway 10 has a problem in the first place. Therefore, a predetermined PMTU value that can avoid the black hole problem is uniformly applied to any communication to the WAN side. As described above, in the above processing, when the number of times that the black hole problem is determined within a predetermined time is equal to or greater than the predetermined number, the minimum MTU is stored in association with all the terminals on the WAN side. And notifies the terminal on the LAN side. For this reason, it is possible to reliably avoid the black hole problem.

  Thus, even if the LAN side terminal does not store the PMTU value up to the destination, the gateway 10 stores the WAN side destination and the reachable PMTU value in association with each other in the management table. The PMTU value that can reach the destination can be acquired by receiving a packet excessive message generated by the gateway 10 in one round-trip communication with the gateway 10, and communication with the destination can be performed using the PMTU value.

  Here, for a pattern in which the PMTU values of all destinations on the WAN side are constant values, the link of the communication interface on the WAN side is reduced without narrowing the link MTU value of the communication interface on the LAN side of the gateway 10 (for example, the link MTU value = 1500 bytes). When the MTU value is narrowed down (for example, the link MTU value = 1280 bytes), the PMTU search (for example, the PMTU value (for example, the link MTU value = 1280 bytes) can be performed by the PMTU search before being transferred from the gateway 10 to the WAN side. , PMTU value = 1280 bytes) is notified to the LAN-side transmission source. The difference between the case where the link MTU value of the WAN-side communication interface is reduced and the configuration of the third embodiment will be described.

  In an environment where a public server or the like is installed on the LAN side of the gateway 10 and the public server is accessed from the WAN side, when communication from the WAN side to the public server is received, the MTU value in this communication is 1500 bytes. Since the link MTU on the WAN side of the gateway 10 is narrowed down (for example, link MTU value = 1280 bytes), the gateway 10 performs a PMTU search so that the communication is adjusted to the link MTU on the WAN side. Based on this, “1280 bytes” is returned as a PMTU to the WAN side transmission source, and even if the MTU value is a path that can communicate with 1500 bytes from the WAN side transmission source to immediately before the gateway 10, the MTU value communicates with 1280 bytes. This is inefficient. On the other hand, in the configuration of the third embodiment described above, it is not necessary to narrow down the link MTU on the WAN side of the gateway 10, so that it functions effectively even in such an environment.

(Fourth embodiment)
By the way, in the present invention, notification of PMTU to be applied not only to a predetermined destination but also to a predetermined address range (for example, WAN-side destination) may be performed.

  Therefore, in the following description of the fourth embodiment, a case will be described in which PMTU notification to be applied to a predetermined address range (for example, WAN-side destination) is performed. Here, when notification of PMTU to be applied to a predetermined address range (for example, all destinations on the WAN side), a new message used between the gateway to notify and the LAN side terminal to receive the notification is defined. There is a need to. Here, an example of two messages will be described.

  Here, the ICMPv6 excessive packet message is defined with type = 2 and code = 0. For example, an undefined code = 1 with type = 2 or a new undefined type may be defined within the specification. The terminal that has received the newly defined message performs processing based on at least the information included in the message. Here, four types (1) to (4) will be described.

  The newly defined message includes a set “destination: PMTU” of “destination” and “PMTU” applied to the destination. The LAN-side terminal that has received the notification of this message communicates with this “destination” using the value of “PMTU”.

  For example, when the newly defined message includes the “destination“ A ”: PMTU“ X ”” group (1), the LAN side terminal that has received the message notification is addressed to a predetermined address A ( X is applied as the PMTU value for communication at the communication destination.

  When the newly defined message includes the “destination“ {R} ”: PMTU“ Y ”” pair (2), the LAN side terminal that has received the message notification transmits the address range {R }, Y is applied as the PMTU value for communications destined for the address included in the. Note that two or more addresses and address ranges may be set, and a field for indicating the address range is provided.

  Further, when the newly defined message includes the “destination“ ¬ {R} ”: PMTU“ Y ”” group (3), for example, the LAN side NW address is included in the address range {R}. If specified, PMTU = Y is applied to communication to a destination other than the LAN side, that is, to the WAN side. This is a negative expression regarding the destination in (2) above. A field will be provided that can represent a logical NOT NOT for an address or address range.

  When the newly defined message includes the destination (¬T): PMTU “Z” (4), the LAN side terminal that has received the message notification participates in the message. The address information of the existing NW domain is acquired, and communication is performed assuming that the destination PMTU other than this address (range) is Z. For example, in the case of IPv4, the address information is obtained by calculating from an IP address, a subnet mask, and the like, and in the case of IPv6, a network prefix and prefix length are obtained. The difference from the above (3) is that the gateway does not explicitly notify the address range but specifies the address range on the terminal side. Note that the gateway 10 stores the information of the “destination: PMTU” set of the “destination” and the “PMTU” applied to the destination in the above four types (1) to (4). .

  There are two timings when the terminal receives notification of a newly defined message. First, the terminal that is the transmission source of the communication to the WAN destination receives the PMTU notification by the ICMPv6 message. In this case, the PMTU notification can be received from the gateway in the process of attempting communication with the destination.

  In addition, when receiving a notification at other timing, the terminal notifies the terminal as a new optional message of a router advertisement advertised by the gateway, and the received terminal sends a PMTU to its own terminal according to the message. It may be set. The contents and processing of the message are the same as (1) to (4) above. In that case, in RA, a new definition is made with an undefined option. In the case of RA, not only the terminal is notified of the reception of the RS but also the gateway voluntarily notifies at a predetermined time interval, so the LAN side terminal receives the notification of the PMTU related to the WAN side. be able to.

  In addition, although embodiment of this invention was described so far, this invention may be implemented with a various different form other than embodiment mentioned above.

[Black hole problem determination]
For example, various different processing methods may be used for determining whether or not a black hole problem has occurred. By the way, in the case of TCP (Transmission Control Protocol), the source is first transmitted by MSS (Maximum Segment Size) adjusted to the smaller size after exchanging each other MSS by 3-way handshake between the source and destination. Although the first communication passes because the packet size is small, there are cases where the packet size of the adjusted MSS after that is large and the communication does not pass.

  As a countermeasure in such a case, a packet for a predetermined number of round trips may be monitored from the start of communication or after the 3-way handshake, and may be determined to be a necessary process when there is no response for a predetermined time.

  Alternatively, the TCP sequence number of the transmitted packet may be stored, and whether or not an ACK (ACKnowledgement) for the sequence number is returned within a predetermined time may be included in the monitoring target. Further, since TCP has retransmission control, if ACK corresponding to the same sequence number of a packet transmitted a predetermined number of times by this retransmission control is not returned, it may be determined that processing is necessary.

  Or, when there is no packet response of the adjusted MSS size within a predetermined time, or when there are more than a predetermined number of responses within a predetermined period of packets less than this MSS size (for example, in the case of a Web site, transmission If only the text file is displayed on the original terminal and indicates that the image file to be displayed or the moving image to be played back is not displayed), it may be determined that a black hole problem has occurred.

  Alternatively, for the black hole problem, since a packet having the minimum MTU size defined in the standard specification passes, only a packet having a size larger than the minimum MTU may be monitored. Alternatively, when it is confirmed that a packet having a size larger than the minimum MTU defined in the standard specification has been transmitted / received, transmitted, and received, it may be determined that the packet is not to be monitored.

  By the way, although it is normal communication without encountering a black hole problem, there is a case where there is no response from the WAN side for communication from the LAN side. In this case, in the case of UDP, whether or not there is a response from the destination depends on the source / destination application using UDP (User Datagram Protocol). Therefore, packet monitoring is performed to identify TCP / UDP, and if it is TCP, it can be determined that there is a return from the WAN side, so the presence or absence of a response is confirmed, and in the case of UDP, there is no UDP return. Application protocols that are known in advance may be excluded from monitoring targets by storing a set of one or more of the protocol, port number, and message in advance at the gateway. Such storage may also be applied to TCP. Note that what is returned in UDP includes, for example, responses to DNS, DHCP, and NTP queries. Further, the monitoring target packet may be larger than the minimum size defined in the standard specification.

  Each terminal may continue to use the PMTU notified from the gateway and communicate with the WAN side, but may refresh (delete) the PMTU after a predetermined time has elapsed. This predetermined time may be included in the notification from the gateway, or may be managed in each terminal. Further, the contents of the management table held by the gateway itself may be refreshed after a predetermined period of time. This is because the route on the Internet changes dynamically, so the same destination is not always the same PMTU.

  The management table does not store the WAN destination to which the PMTU should be notified, but stores the WAN side destination that does not need to notify the PMTU to the terminal on the LAN side, and the WAN side that is not stored in the management table When receiving a packet addressed to the destination, the PMTU may be notified. Further, the source and destination information handled by the management table may be name information obtained from a DNS (Domain Name System) instead of an address. The gateway may be a portable medium such as a mobile router.

  Even in the case of IPv6 on Ethernet, if a tunnel is set up on the route, it is necessary to consider the header size for the tunnel, including the overhead size for this tunnel. A predetermined PMTU value such that MTU = 1280 may be set. Further, it is not necessary for the destination to be able to acquire an appropriate PMTU by the PMTU search to manage communication by the gateway, and only the destination that encounters the black hole problem may be stored.

[System configuration, etc.]
Further, each component of each illustrated apparatus is functionally conceptual, and does not necessarily need to be physically configured as illustrated. In other words, the specific form of distribution / integration of each device is not limited to that shown in the figure, and all or a part thereof may be functionally or physically distributed or arbitrarily distributed in arbitrary units according to various loads or usage conditions. Can be integrated and configured. For example, the cache search unit 13a and the disk load determination unit 13b may be integrated. Further, all or any part of each processing function performed in each device may be realized by a CPU and a program analyzed and executed by the CPU, or may be realized as hardware by wired logic.

  In addition, among the processes described in this embodiment, all or part of the processes described as being performed automatically can be performed manually, or the processes described as being performed manually can be performed. All or a part can be automatically performed by a known method. In addition, the processing procedure, control procedure, specific name, and information including various data and parameters shown in the above-described document and drawings can be arbitrarily changed unless otherwise specified.

[program]
It is also possible to create a program in which the processing executed by the gateway 10 described in the above embodiment is described in a language that can be executed by a computer. For example, it is possible to create a relay program in which processing executed by the gateway 10 is described in a language that can be executed by a computer. In this case, when the computer executes the relay program, the same effect as in the above embodiment can be obtained. Further, the same processing as in the above embodiment may be realized by recording such a relay program on a computer-readable recording medium, and reading and executing the relay program recorded on the recording medium. An example of a computer that executes a relay program that implements the same function as that of the gateway 10 illustrated in FIG. 2 will be described below.

  FIG. 17 is a diagram illustrating a computer 1000 that executes a relay program. As illustrated in FIG. 17, the computer 1000 includes, for example, a memory 1010, a CPU 1020, a hard disk drive interface 1030, a disk drive interface 1040, a serial port interface 1050, a video adapter 1060, and a network interface 1070. These units are connected by a bus 1080.

  The memory 1010 includes a ROM (Read Only Memory) 1011 and a RAM 1012 as illustrated in FIG. The ROM 1011 stores a boot program such as BIOS (Basic Input Output System). The hard disk drive interface 1030 is connected to the hard disk drive 1031 as illustrated in FIG. The disk drive interface 1040 is connected to the disk drive 1041 as illustrated in FIG. For example, a removable storage medium such as a magnetic disk or an optical disk is inserted into the disk drive. The serial port interface 1050 is connected to, for example, a mouse 1051 and a keyboard 1052 as illustrated in FIG. The video adapter 1060 is connected to a display 1061, for example, as illustrated in FIG.

  Here, as illustrated in FIG. 17, the hard disk drive 1031 stores, for example, an OS 1091, an application program 1092, a program module 1093, and program data 1094. That is, the relay program is stored in, for example, the hard disk drive 1031 as a program module in which a command executed by the computer 1000 is described. For example, a program module 1093 in which a message transmission procedure for executing information processing similar to the message transmission unit 131 illustrated in FIG. 3 and a message storage procedure for executing information processing similar to the message storage unit 132 are described Stored in the drive 1031. Alternatively, when the message transmission unit 131 is distributed between the comparison unit and the transmission unit as in the above example, the program module 1093 describing the comparison procedure, the transmission procedure, and the message storage procedure is stored in the hard disk drive. 1031 is stored.

  Various data held by the storage unit 13 described in the above embodiment is stored as program data in, for example, the memory 1010 or the hard disk drive 1031. Then, the CPU 1020 reads the program module 1093 and program data 1094 stored in the memory 1010 and the hard disk drive 1031 to the RAM 1012 as necessary, and executes a message transmission procedure (or comparison procedure and transmission procedure) and a message storage procedure. .

  Note that the program module 1093 and the program data 1094 related to the relay program are not limited to being stored in the hard disk drive 1031, but may be stored in, for example, a removable storage medium and read out by the CPU 1020 via the disk drive or the like. Good. Alternatively, the program module 1093 and the program data 1094 related to the relay program are stored in another computer connected via a network (LAN (Local Area Network), WAN (Wide Area Network), etc.), and via the network interface 1070. May be read by the CPU 1020.

10, 10A Gateway 11, 12 Communication unit 13 Storage unit 14 Communication monitoring unit 15 PMTU notification determination unit 16 PMTU notification unit 20A to 20C Terminal 21 Notification unit 22 PMTU setting unit 30 Router 40 LAN
50 WAN
100 network system

Claims (7)

A relay device that relays communication between a wide area communication network and a local communication network,
A monitoring unit that monitors a response to data transmission from the local communication network side terminal to the wide area network side terminal;
A determination unit that determines whether a response is returned within a predetermined time based on monitoring by the monitoring unit;
When the determination unit determines that there is no response within a predetermined time, the transfer has a data capacity that can be transferred at once and that is smaller than the data capacity at the time of data transmission. A relay unit, comprising: a notification unit that generates a message indicating a possible capacity and notifies the message to a terminal on the local communication network side. If it is determined by the determination unit that there is no response within a predetermined time, data having a smaller data capacity than that when data is transmitted from a terminal on the local communication network side to a terminal on the wide area network side Further comprising a confirmation unit for transmitting to a terminal on the communication network side and confirming whether a response to the transmission is within a predetermined time;
When the confirmation unit confirms that there is a response within a predetermined time, the notification unit generates a message indicating the transferable capacity and notifies the message to the terminal on the local communication network side The relay apparatus according to claim 1. A storage unit that stores the destination information in the terminal on the wide area network side in association with the transferable capacity when performing data communication with the terminal on the wide area network side;
When the data communication from the local communication network side terminal to the wide area network side terminal is performed, the monitoring unit stores destination information corresponding to the destination information of the wide area network side terminal in the storage unit. If it is, monitor whether the transferable capacity in the data communication is larger than the transferable capacity stored in association with the destination information,
When the transferable capacity in the data communication is larger than the transferable capacity stored in association with the destination information, the notification unit stops data communication to the terminal on the wide area network side, and the destination The relay apparatus according to claim 1 or 2, wherein a message indicating a transferable capacity stored in association with information is generated, and the message is notified to a terminal on the local communication network side.   If the number of times that the determination unit determines that there is no response within a predetermined time is greater than or equal to a predetermined number, the notification unit responds to data transmission to all terminals on the wide area network side. The relay apparatus according to claim 1, wherein a message instructing a minimum transferable capacity is generated and the message is notified to a terminal on the local communication network side.   The notification unit generates a message indicating an address range and a transferable capacity applied to communication addressed to the address range, or a transferable capacity applied to communication to an address or a destination other than the address range, and the message The relay apparatus according to any one of claims 1 to 4, wherein the message is notified to a terminal on the local communication network side. A relay method executed by a relay device that relays communication between terminals between a wide area communication network and a local communication network,
A monitoring step of monitoring a response to data transmission from the local communication network side terminal to the wide area network side terminal;
A determination step of determining whether a response is returned within a predetermined time based on the monitoring by the monitoring step;
When it is determined by the determination step that there is no response within a predetermined time, the transfer has a data capacity that can be transferred at one time and that is smaller than the data capacity at the time of data transmission. And a notification step of generating a message indicating the available capacity and notifying the message to the terminal on the local communication network side.   The relay program for functioning a computer as a relay apparatus of Claims 1-5.

Images