Switch, frame relay method, and frame relay program

Abstract

This switch (100) comprises a plurality of ports including one or more normal ports and one or more redundant ports. The switch receives a communication frame delivered to each of the plurality of ports, transmits the received communication frame from a normal port when the received communication frame is a frame addressed to the normal port, and transmits the received communication frame from all the redundant ports excluding a reception port when the received communication frame is not a frame addressed to the normal port.

Description

Switch, frame relay method, and frame relay program

[0001] The present disclosure relates to a switch that relays communication frames.

[0002] In IEEE 802.1CB, which realizes communication redundancy, a switch relays communication frames by duplicating a communication frame sent from a communication device and transmitting the same communication frame from multiple ports. When the same communication frame is received on multiple ports, the switch relays only the first communication frame received and discards communication frames received after the first. This realizes communication redundancy in a topology in which multiple paths run in parallel. However, IEEE 802.1CB does not clarify how to set up redundant communication paths.

[0003] Patent Document 1 discloses the following method for setting up communication paths. In the method of Patent Document 1, the MAC addresses of communication devices connected to each port of each switch are registered in each switch. In other words, the method of Patent Document 1 requires that the MAC addresses of all connected communication devices be registered in all switches. Therefore, the method of Patent Document 1 cannot automatically handle changes in MAC addresses that occur when a communication device is replaced during operation.

[0004] Japanese Patent Application Laid-Open No. 2017-011566

[0005] The present disclosure aims to enable automatic redundant communication even when a MAC address accompanying replacement of a communication device during operation is not known.

[0006] The switch of the present disclosure is a switch that relays communication frames communicated between multiple communication devices, and includes a plurality of ports including one or more normal ports and one or more redundant ports; a receiving unit that receives communication frames that have arrived at each of the plurality of ports; and a transmitting unit that, if the received communication frame is a frame addressed to a normal port, transmits the received communication frame from the normal port, and, if the received communication frame is not a frame addressed to the normal port, transmits the received communication frame from all redundant ports except the receiving port.

[0007] According to the present disclosure, redundant communication can be automatically performed even if the MAC address associated with the replacement of an operating communication device is not known.

[0008] FIG. 1 is a diagram showing an example of the configuration of a communication system 200 according to a first embodiment. FIG. 2 is a diagram showing an example of the configuration of a switch 100 according to the first embodiment. FIG. 3 is a diagram showing an example of the configuration of a communication device 210 according to the first embodiment. A flowchart of a frame relay method according to the first embodiment. A flowchart of a frame relay method according to the first embodiment. A diagram explaining non-redundancy in MAC address learning. A flowchart of a frame relay method according to a second embodiment. A flowchart of a frame relay method according to a third embodiment. A flowchart of the operation of a communication device 210 according to a fourth embodiment. A diagram showing an example of the configuration of a communication system 200 according to the first embodiment. A diagram showing an example of the configuration of a communication system 200 according to the first embodiment.

[0009] In the embodiments and drawings, the same or corresponding elements are denoted by the same reference numerals. The description of elements denoted by the same reference numerals as those already described will be omitted or simplified as appropriate. Arrows in the drawings primarily indicate the flow of data or the flow of processing.

[0010] First Embodiment A switch 100 that relays communication frames will be described with reference to FIGS.

[0011] ***Description of Configuration*** The configuration of a communication system 200 will be described with reference to Fig. 1. The communication system 200 includes a plurality of communication devices 210 and a plurality of switches 100. The plurality of communication devices 210 and the plurality of switches 100 form a network.

[0012] Each communication device 210 is connected to one of the switches 100 using a communication cable. Multiple switches 100 are connected to each other using communication cables. The communication cables form a communication path between the communication device 210 and the switch 100 or a communication path between two switches 100.

[0013] The plurality of communication devices 210 transmit and receive communication frames to and from each other via one or more switches 100. Each switch 100 relays communication frames communicated between the plurality of communication devices 210. The switch 100 is also called a relay device.

[0014] The configuration of the switch 100 will be described with reference to Fig. 2. The switch 100 includes a processing circuit 101 and a plurality of ports 102. The processing circuit 101 and the plurality of ports 102 are connected via signal lines.

[0015] 2, the switch 100 has three ports 102. However, the switch 100 may have two ports 102 or four or more ports 102.

[0016] The processing circuit 101 includes elements such as a receiving unit 111 , a transmitting unit 112 , and a storage unit 120 .

[0017] The processing circuitry 101 is hardware that realizes the receiving unit 111, the transmitting unit 112, and the storage unit 120. The processing circuitry 101 may be dedicated hardware, or may be a processor that executes a program stored in a memory.

[0018] When the processing circuit 101 is dedicated hardware, the processing circuit 101 may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field Programmable Gate Array.

[0019] When the processing circuit 101 is a processor that executes a program stored in memory, the processing circuit 101 constitutes a computer. The receiving unit 111 and the transmitting unit 112 can be realized by software. A program that causes a computer to function as the receiving unit 111 and the transmitting unit 112 is called a frame relay program. The frame relay program is stored in memory and executed by the processor. The frame relay program can be recorded (stored) in a computer-readable manner on a non-volatile recording medium such as an optical disk or flash memory.

[0020] The storage unit 120 can be realized by a memory. The storage unit 120 stores an address table 121 and the like. The address table 121 will be described later.

[0021] The configuration of the communication device 210 will be described with reference to Fig. 3. The communication device 210 includes a processing circuit 211 and a port 214. The processing circuit 211 and the port 214 are connected via a signal line.

[0022] The processing circuit 211 includes elements such as a transmitting unit 212 and a receiving unit 213 .

[0023] The processing circuitry 211 is hardware that realizes the transmitting unit 212 and the receiving unit 213. The processing circuitry 211 may be dedicated hardware, or may be a processor that executes a program stored in a memory.

[0024] ***Explanation of Operation*** The operation procedure of the switch 100 corresponds to a frame relay method. The operation procedure of the switch 100 corresponds to a processing procedure by a frame relay program. The frame relay method will be described below.

[0025] The multiple ports 102 of the processing circuit 101 will be described with reference to FIG. 1 . The multiple ports 102 are classified into normal ports and redundant ports. In FIG. 1 , solid arrows indicate the flow of communication frames transmitted from normal ports, and dashed arrows indicate the flow of communication frames transmitted from redundant ports. A normal port is a port 102 connected via a single path to a communication device 210 among multiple communication devices 210 for which no alternative path exists between the device and the switch 100. For example, a communication device (A1) is connected to a switch (A) via a single communication path. In other words, no alternative path exists between the communication device (A1) and the switch (A). Therefore, among the multiple ports 102 of the switch (A), the port 102 to which the communication device (A1) is connected is a normal port. Similarly, among the multiple ports 102 of the switch (A), the port 102 to which the communication device (A2) is connected is a normal port. A redundant port is a port that is not a normal port. Specifically, a redundant port is a port 102 that is connected via multiple paths to a communication device 210 among multiple communication devices 210 for which an alternative path exists between the communication device 210 and the switch 100. For example, among the multiple ports 102 of a switch (A), three ports 102 that are neither a normal port connected to a communication device (A1) nor a normal port connected to a communication device (A2) are redundant ports. Each of six communication devices (B1, B2, C1, C2, D1, D2) is connected to the switch (A) via two or more communication paths. In other words, an alternative communication path exists between each of the six communication devices (B1, B2, C1, C2, D1, D2) and the switch (A) via one or more switches 100. In each switch 100, the multiple ports 102 are classified into normal ports and redundant ports according to user settings.

[0026] A communication frame will now be described. A source address, a destination address, and a sequence number are set in a communication frame. The source address is the address of the communication device 210 that is the source of the communication frame. The destination address is the address of the communication device 210 that is the destination of the communication frame. A MAC address is used as the address of the communication device 210. MAC is an abbreviation for Media Access Control.

[0027] The communication device 210 will now be described. The transmitter 212 of the source communication device 210 transmits a communication frame from a port 214. The transmitted communication frame passes through one or more switches 100 and arrives at the destination communication device 210. The receiver 213 of the destination communication device 210 receives the communication frame that has arrived at the port 214.

[0028] 4 and 5, the frame relay method will be described. Steps S101 to S113 are executed in each switch 100 every time a communication frame arrives at any of the ports 102 of the switch 100. The port 102 at which the communication frame arrives is referred to as the receiving port.

[0029] In step S101, the receiver 111 receives a communication frame that has arrived at a reception port. The received communication frame is referred to as a received frame.

[0030] In step S102, the receiving unit 111 determines whether the receiving port is a normal port or a redundant port.

[0031] For example, the receiving unit 111 makes the determination by referring to a port table. The port table indicates the type of port 102 (normal port or redundant port) for each port 102. Specifically, the port table indicates the port type in association with the port identifier for each port 102. The port table is created by a user and stored in advance in the storage unit 120. The receiving unit 111 refers to the port table and determines whether the port type associated with the port identifier of the receiving port is a normal port or a redundant port.

[0032] If the receiving port is a normal port, the process proceeds to step S103. If the receiving port is a redundant port, the process proceeds to step S105.

[0033] In step S103 , the receiving unit 111 determines whether the source address of the received frame is registered in the address table 121 .

[0034] The address table 121 registers the address of the communication device 210 connected to each normal port. Specifically, the address table 121 registers the address of the communication device 210 associated with the port identifier for each normal port. The receiving unit 111 determines whether the same address as the source address set in the received frame is registered in the address table 121 associated with the port identifier of the receiving port.

[0035] If the source address of the received frame is registered in the address table 121, the process proceeds to step S106. If the source address of the received frame is not registered in the address table 121, the process proceeds to step S104.

[0036] In step S104, the receiving unit 111 registers the source address of the received frame in the address table 121 in association with the receiving port.

[0037] Specifically, the receiver 111 registers the source address of the received frame in the address table 121 in association with the port identifier of the receiving port.

[0038] In step S105, the receiving unit 111 determines whether or not a communication frame identical to the received frame has already been received.

[0039] A communication frame that is the same as the received frame is a communication frame that has arrived at one of the redundant ports of the switch 100 via a communication path different from the communication path of the received frame before the received frame reaches the receiving port of the switch 100. The set of source address, destination address, and sequence number set in the communication frame that is the same as the received frame matches the set of source address, destination address, and sequence number set in the received frame.

[0040] For example, the receiving unit 111 makes a determination by referring to a communication table. In the communication table, a sequence number is registered in association with each source address. When a communication frame is received, the receiving unit 111 searches the communication table for a sequence number associated with the same source address as the source address set in the received communication frame. If the found sequence number is smaller than the sequence number set in the received communication frame, the receiving unit 111 updates the found sequence number to the sequence number set in the received communication frame. The receiving unit 111 searches the communication table for a sequence number associated with the same source address as the source address set in the received frame. If the found sequence number is equal to or greater than the sequence number set in the received frame, the receiving unit 111 determines that a communication frame identical to the received frame has already been received. Alternatively, the receiving unit 111 may make a determination by referring to the communication table as follows: In the communication table, a sequence number is registered in association with each source address. When a communication frame is received, the receiving unit 111 searches the communication table for a sequence number associated with the same source address as the source address set in the received communication frame. If the sequence number set in the received communication frame is not found, the receiving unit 111 registers the sequence number set in the received communication frame. If the sequence number set in the received communication frame is found, the receiving unit 111 determines that the same communication frame as the received frame has already been received.

[0041] If a communication frame identical to the received frame has already been received, the received frame is not relayed because the same communication frame as the received frame has already been relayed, and the process ends.

[0042] If a communication frame identical to the received frame has not been received, the process proceeds to step S106.

[0043] In step S 106 , the receiving unit 111 passes the received frame and the receiving port identifier to the transmitting unit 112 .

[0044] After step S106, the process proceeds to step S111.

[0045] In step S111 , the transmitting unit 112 determines whether the destination address of the received frame is registered in the address table 121 .

[0046] Specifically, the transmitting unit 112 determines whether the same address as the destination address set in the received frame is registered in the address table 121.

[0047] If the destination address of the received frame is registered in the address table 121, the process proceeds to step S112. If the destination address of the received frame is not registered in the address table 121, the process proceeds to step S113.

[0048] In step S112, the transmitter 112 transmits the received frame from the corresponding port, thereby relaying the received frame.

[0049] The corresponding port is a normal port to which the communication device 210 that is the destination of the received frame is connected.

[0050] The corresponding port is determined using the address table 121. The transmitter 112 refers to the address table 121 and determines that the normal port corresponding to the destination address of the received frame is the corresponding port. Specifically, the transmitter 112 finds, in the address table 121, a port identifier that is associated with the same address as the destination address set in the received frame. The port 102 identified by the found port identifier is the corresponding port.

[0051] After step S112, the process ends.

[0052] In step S113, the transmitter 112 transmits the received frame from all redundant ports except the receiving port, thereby relaying the received frame.

[0053] Received frames are duplicated and transmitted.

[0054] The redundant port is determined using, for example, a port table.

[0055] After step S113, the process ends.

[0056] ***Effects of First Embodiment*** The method of Patent Document 1 cannot automatically accommodate MAC address changes that occur when a communication device is replaced. One method for accommodating MAC address changes is MAC address learning. MAC address learning is a function that registers the correspondence between the source MAC address of a received communication frame and the receiving port, and then transmits the communication frame from the port corresponding to the MAC address that matches the destination MAC address of the subsequently received communication frame. However, using MAC address learning makes it impossible to achieve redundancy as described below. In FIG. 6, to achieve communication redundancy from communication device (3) to communication device (1), it is desirable to also be able to use the communication path indicated by the dashed arrow. However, MAC address learning makes it possible to use only the communication path indicated by the double arrow.

[0057] On the other hand, the first embodiment has the following features. A port of a switch that connects sections in a target network for which no alternative path exists is defined as a normal port. A port of a switch that connects sections for which an alternative path exists is defined as a redundant port. The switch uses a MAC address learning function to register only the MAC addresses of communication devices connected to the normal port. When a communication frame addressed to an unregistered MAC address is received, the switch relays and transmits the frame using all redundant ports except the receiving port.

[0058] The features of the first embodiment are detailed as follows: Each switch registers the MAC address of a communication device connected beyond a normal port by MAC address learning, and performs relay transmission as follows: 1) If the communication device with the destination address of the received communication frame is not connected beyond any of the normal ports of the switch itself, the received communication frame is duplicated and relayed using all redundant ports other than the receiving port. 2) If the communication device with the destination address of the received communication frame is connected beyond a normal port of the switch itself, relay transmission is performed using only that normal port.

[0059] The first embodiment provides the following advantages. The switch uses the MAC address learning function to register only the MAC addresses of communication devices connected to the normal ports, and determines that unregistered MAC addresses are connected to redundant ports. This makes it possible to automatically respond to changes in MAC addresses that occur when an active communication device is replaced. The switch relays and transmits communication frames addressed to unregistered MAC addresses using all redundant ports except the receiving port. This makes it possible to achieve communication redundancy.

[0060] Second Embodiment A second embodiment in which the address table 121 is created in advance will be described, focusing mainly on the differences from the first embodiment, with reference to FIG.

[0061] ***Description of Configuration*** The configurations of the communication system 200, the switch 100 and the communication device 210 are the same as those in the first embodiment.

[0062] ***Explanation of Operation*** The address table 121 is created by the user and stored in advance in the storage unit 120 of the switch 100.

[0063] The frame relay method will be described with reference to Fig. 7. In step S101, the receiving unit 111 receives a communication frame that has arrived at a receiving port. Step S101 is the same as that described in the first embodiment.

[0064] After step S101, the process proceeds to step S201.

[0065] In step S201, the receiving unit 111 determines whether the receiving port is a normal port or a redundant port. The determination method is the same as the method in step S102 in the first embodiment.

[0066] If the receiving port is a normal port, the process proceeds to step S106, whereas if the receiving port is a redundant port, the process proceeds to step S105.

[0067] Steps S105, S106 and the subsequent steps are the same as those in the first embodiment.

[0068] ***Effects of the Second Embodiment*** In the first embodiment, when creating an address table by MAC address learning, the communication device connected to the normal port must communicate at least once. Until the MAC address is registered by MAC address learning, communication frames addressed to the communication device connected to the normal port cannot be relayed.

[0069] The second embodiment has the following features: The MAC addresses of the communication devices connected to the normal ports are registered in the address table 121 by the user, not by MAC address learning.

[0070] The features of the second embodiment are detailed as follows: The MAC addresses of the communication devices connected to the normal ports are registered by the user, and each switch relays and transmits as follows: 1) If the communication device with the destination address of the received communication frame is not connected to any of the normal ports of its own switch, the received communication frame is duplicated and relayed and transmitted using all redundant ports other than the receiving port. 2) If the communication device with the destination address of the received communication frame is connected to a normal port of its own switch, the frame is relayed and transmitted using only that normal port.

[0071] The second embodiment has the following advantages: Even before a communication device connected to a normal port starts communication, the switch can correctly relay and transmit a packet addressed to that communication device.

[0072] Third Embodiment A third embodiment will be described with reference to FIG. 8, which mainly describes the differences from the first embodiment with respect to a configuration that enables relaying of a communication frame addressed to an uncommunicated communication device 210 connected to a normal port even if the address table 121 is not created in advance.

[0073] ***Description of Configuration*** The configurations of the communication system 200, the switch 100 and the communication device 210 are the same as those in the first embodiment.

[0074] ***Description of Operation*** The frame relay method will be described with reference to Fig. 8. Steps S101 to S106 are as described in embodiment 1. After step S106, the process proceeds to step S301.

[0075] In step S301, the transmitting unit 112 determines whether the destination address of the received frame is registered in the address table 121. The method of determination is the same as the method of step S111 in the first embodiment.

[0076] If the destination address of the received frame is registered in the address table 121, the process proceeds to step S112. If the destination address of the received frame is not registered in the address table 121, the process proceeds to step S302.

[0077] In step S112, the transmitter 112 transmits the received frame from the corresponding port. This relays the received frame. Step S112 is the same as that described in the first embodiment.

[0078] In step S302, the transmitter 112 transmits the received frame from all redundant ports excluding the receiving port. Furthermore, the transmitter 112 transmits the received frame from all normal ports excluding the receiving port. In this way, the received frame is relayed.

[0079] ***Effects of the Third Embodiment*** In the first embodiment, when creating an address table by MAC address learning, the communication device connected to the normal port needs to communicate at least once. Until the MAC address is registered by MAC address learning, communication frames addressed to the communication device connected to the normal port cannot be relayed.

[0080] The third embodiment has the following features: The switch relays communication frames having an unregistered MAC address as a destination address using not only a redundant port but also a normal port.

[0081] The features of the third embodiment are detailed as follows: Each switch registers the MAC address of a communication device connected beyond a normal port by MAC address learning, and performs relay transmission as follows: 1) and 2). 1) If the communication device with the destination address of the received communication frame is not connected beyond any normal port of the switch itself, the received communication frame is duplicated and relayed using all redundant ports and normal ports other than the receiving port. 2) If the communication device with the destination address of the received communication frame is connected beyond a normal port of the switch itself, relay transmission is performed using only that normal port.

[0082] The third embodiment has the following advantages: Even before a communication device connected to a normal port starts communication, the switch can correctly relay and transmit a packet addressed to that communication device.

[0083] Fourth Embodiment A fourth embodiment in which the addresses of communication devices 210 connected to normal ports can be registered in advance in the address table 121 will be described with reference to FIG.

[0084] ***Description of Configuration*** The configurations of the communication system 200, the switch 100 and the communication device 210 are the same as those in the first embodiment.

[0085] ***Description of Operation*** The operation of the communication device 210 will be described with reference to Fig. 9. In step S401, the port 214 detects connection of the communication system 200 to the network.

[0086] For example, the connection of the communication system 200 to the network is detected as follows: A user connects one end of a communication cable to a normal port of the switch 100 and connects the other end of the communication cable to the port 214 of the communication device 210. The port 214 of the communication device 210 detects the connection of the communication cable.

[0087] In step S402 , the transmitter 212 creates a communication frame for the entire network of the communication system 200 , and transmits the created communication frame from the port 214 .

[0088] A communication frame addressed to the entire network of the communication system 200 is a communication frame addressed to all of the communication devices 210 and reaches all of the communication devices 210. For example, if the network of the communication system 200 is Ethernet, the transmitter 212 transmits a communication frame with a broadcast address set as the destination address.

[0089] A communication frame to the entire network of the communication system 200 is relayed by one or more switches 100 and reaches all communication devices 210 except for the communication device 210 from which it originated.

[0090] When a communication frame for the entire network of the communication system 200 arrives at the port 102, the switch 100 executes the frame relay method in the same way as when a normal communication frame arrives. If the receiving port is a normal port, the address of the source communication device 210 is registered in the address table 121 in association with the normal port that is the receiving port (step S104).

[0091] ***Effects of the Fourth Embodiment*** In the first embodiment, when creating an address table by MAC address learning, the communication device connected to the normal port needs to communicate at least once. Until the MAC address is registered by MAC address learning, communication frames addressed to the communication device connected to the normal port are not relayed.

[0092] The fourth embodiment has the following features: Each communication device performs communication that reaches the entire network once when a port is connected.

[0093] The features of the fourth embodiment are detailed as follows: When a port is connected, each communication device performs communication once that reaches the entire network. Each switch registers the MAC address of the communication device connected beyond its normal port using MAC address learning, and performs relay transmission as follows: 1) If the communication device with the destination address of the received communication frame is not connected beyond any of the normal ports of its own switch, the received communication frame is duplicated and relayed using all redundant ports other than the receiving port. 2) If the communication device with the destination address of the received communication frame is connected beyond a normal port of its own switch, relay transmission is performed using only that normal port.

[0094] The fourth embodiment has the following advantages: Relay transmission to a communication device can be performed correctly.

[0095] *** Supplementary Notes on the Embodiment *** A supplementary explanation of normal ports will be provided based on FIGS. 10 and 11 . Normal ports include ports connected to adjacent communication devices 210 via a single path, as well as ports connected to adjacent switches 100 via a single path. In FIG. 10 , the right port of switch (B) has an alternative path between it and switches (F, G, H, I). However, the right port of switch (B) does not have an alternative path between it and switch (E). Therefore, the right port of switch (B) is a normal port in relation to switch (E). Note that the right port of switch (B) is a port (normal port) connected to communication device (E1), which does not have an alternative path between it and switch (B), via a single path (B → E → E1). In FIG. 11 , there is an alternative path between the right port of switch (B) and switch (E). For example, in addition to the path (B → E), there is a path (B → C → I → F → E). Therefore, the right port of switch (B) is not a normal port but a redundant port. The right port of switch (B) is a port (redundant port) connected to communication device (E1) through multiple paths (B → E → E1, B → C → I → F → E → E1, etc.) that have alternative paths between it and switch (B).

[0096] Each embodiment is an example of a preferred embodiment and is not intended to limit the technical scope of the present disclosure. Each embodiment may be implemented in part or in combination with other embodiments. Procedures described using flowcharts, etc. may be modified as appropriate.

[0097] Each element of the switch 100 and the communication device 210 may be implemented by software, hardware, firmware, or a combination of these. The term "part" in each element of the switch 100 and the communication device 210 may be interpreted as "processing," "step," "circuit," or "circuitry."

[0098] In an embodiment, a switch that relays communication frames communicated between a plurality of communication devices is disclosed. The switch includes: a plurality of ports that are classified into normal ports connected via a single path to communication devices among the plurality of communication devices that have no alternative path between them and the switch, and redundant ports that are ports other than normal ports; a receiver that receives communication frames that arrive at each of the plurality of ports; and a transmitter that determines, for each normal port, whether a destination address of a received communication frame is registered in an address table in which addresses of communication devices connected to the normal port are registered, and transmits the received communication frame from the normal port corresponding to the destination address if the destination address is registered in the address table, and transmits the received communication frame from all redundant ports except for the receiver port through which the received communication frame arrived if the destination address is not registered in the address table.

[0099] The receiving unit determines whether the receiving port is a normal port and the source address of the received communication frame is registered in the address table, and if the receiving port is a normal port and the source address is not registered in the address table, it registers the source address in the address table in correspondence with the receiving port.

[0100] If the destination address is not registered in the address table, the transmitting unit transmits the received communication frame from all redundant ports other than the receiving port and all normal ports other than the receiving port.

[0101] When a communication device among the plurality of communication devices connected to a normal port of the switch is connected to the normal port of the switch, it transmits a communication frame that reaches all of the plurality of communication devices except for its own communication device, and the receiving unit receives the communication frame that has arrived at the normal port and registers the source address of the received communication frame in the address table in correspondence with the normal port.

[0102] 100 Switch, 101 Processing circuit, 102 Port, 111 Receiving unit, 112 Transmitting unit, 120 Storage unit, 121 Address table, 200 Communication system, 210 Communication device, 211 Processing circuit, 212 Transmitting unit, 213 Receiving unit, 214 Port.

Claims

1. A switch that relays communication frames communicated between multiple communication devices, comprising: a plurality of ports including one or more normal ports and one or more redundant ports; a receiver that receives communication frames that arrive at each of the plurality of ports; and a transmitter that, if the received communication frame is addressed to a normal port, transmits the received communication frame from the normal port, and, if the received communication frame is not addressed to the normal port, transmits the received communication frame from all redundant ports excluding the receiving port.

2. The switch according to claim 1, wherein the normal port is connected to the communication device via a single path with no alternative path present, and the redundant port is a port other than the normal port.

3. The switch according to claim 1 or claim 2, wherein the transmitting unit stores the address of the communication device connected to the normal port.

4. The switch according to claim 1 or 2, wherein the receiving unit stores the source address of a communication frame that has arrived at the normal port in association with the normal port.

5. A frame relay method using a switch that relays communication frames communicated between multiple communication devices, wherein the switch has multiple ports including one or more normal ports and one or more redundant ports, receives communication frames that have arrived at each of the multiple ports, and if the received communication frame is a frame addressed to a normal port, transmits the received communication frame from the normal port, and if the received communication frame is not a frame addressed to the normal port, transmits the received communication frame from all redundant ports except the receiving port.

6. A frame relay program for causing a switch that relays communication frames communicated between a plurality of communication devices to execute reception processing and transmission processing, wherein the switch has a plurality of ports including one or more normal ports and one or more redundant ports, the reception processing receives communication frames that have arrived at each of the plurality of ports, and the transmission processing transmits the received communication frame from the normal port if the received communication frame is a frame addressed to a normal port, and transmits the received communication frame from all redundant ports excluding the reception port if the received communication frame is not a frame addressed to the normal port.

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