Relay device, computer program, and relay method

Abstract

A relay device (1) performs communication in accordance with the IEEE 802.1CB standard via Ethernet (registered trademark) and includes a plurality of ports (14), a MAC address table (12), and an arbitration unit (16). Upon receiving a frame, the arbitration unit (16) performs a learning process of overwriting port information in the MAC address table (12) corresponding to a source MAC address of the frame with the port information indicating the reception port of the frame. If the arbitration unit has determined that the received frame includes an R-TAG (30), the arbitration unit does not perform the learning process corresponding to the reception of the frame.

Description

Relay Device, Computer Program, and Relay Method Cross - Reference to Related Applications 【0001】 This international application claims the benefit of Japanese Patent Application No. 2024 - 218661, filed with the Japan Patent Office on December 13, 2024, the entire disclosure of which is incorporated herein by reference. 【0002】 This disclosure relates to a relay device, a computer program, and a relay method for relaying frames in Ethernet (registered trademark) communication. 【0003】 In IEEE (Institute of Electrical and Electronics Engineers) 802.1CB, a communication protocol for transmitting frames from a Talker to a Listener via multiple redundant paths in Ethernet communication is defined. According to this communication protocol, a relay device connected to the Talker duplicates the frames received from the Talker, attaches an R - TAG (Redundancy TAG) to each frame, and transfers them as redundant frames to each redundant path. Then, when the relay device connected to the Listener receives redundant frames from each redundant path, it transfers only the first - received redundant frame to the Listener, and discards the later - received redundant frames. 【0004】 Also, Patent Document 1 below describes a relay device having a MAC (Media Access Control) address table and an address learning function. The MAC address table is a table in which the MAC address of a communication terminal is associated with port information indicating the port to which a frame having the MAC address as the destination MAC address is transferred when received. Hereinafter, each combination of a MAC address and the port information corresponding to the MAC address in the MAC address table is referred to as a MAC learning entry. 【0005】The address learning function is a function that performs the following processing when a relay device receives a frame. Specifically, if there is no MAC learning entry in the relay device's MAC address table that has a MAC address that matches the source MAC address of the frame, the combination of the source MAC address of the frame and the port number that received the frame is newly registered in the MAC address table as a MAC learning entry. On the other hand, if there is a MAC learning entry in the MAC address table that has a MAC address that matches the source MAC address of the frame, the port information of that MAC learning entry is overwritten with the port information indicating the port that received the frame. 【0006】 Patent No. 6667742 【0007】 However, after a detailed examination, the following issues were identified. 【0008】 Consider the case where a relay device connected to a Listener has the address learning function described above, when a Talker communicates with a Listener multiple times in accordance with the above communication protocol (hereinafter referred to as redundant communication). In this case, due to fluctuations in the communication load on the relay device on the redundant path, the redundant path traversed by each redundant frame that arrives first in each redundant communication may differ. In this case, the relay device connected to the Listener receives the first redundant frame from a different port for each redundant communication. As a result, the port information associated with the Talker's MAC address in the relay device's MAC address table may change frequently. In other words, the port to which the relay device forwards a frame when it receives a frame with the Talker's MAC address as the destination MAC address may change frequently. 【0009】 One aspect of this disclosure is the provision of a technique to suppress frequent changes in the port through which frames are forwarded in a relay device. 【0010】One aspect of this disclosure is a relay device (1) that performs communication in accordance with the IEEE (Institute of Electrical and Electronics Engineers) 802.1CB standard using Ethernet (registered trademark), comprising a plurality of ports (14), an address table (12), an update unit (16), and a determination unit (S205, S500). The ports transmit and receive frames. The address table associates terminal information indicating a communication terminal (2) with port information indicating the port to which a frame destined for the communication terminal is forwarded when such a frame is received. The update unit is configured to perform a learning process (S300, S505) when a frame is received, which is a process to overwrite the port information in the address table corresponding to the terminal information indicating the source communication terminal of the frame with the port information indicating the port that received the frame. The determination unit is configured to determine whether or not the received frame contains an R-TAG (30). The update unit is configured not to perform the learning process corresponding to the reception of a frame if the determination unit determines that the received frame contains an R-TAG. 【0011】 With this configuration, if a received frame contains an R-TAG, the address table is not overwritten in response to the receipt of that frame, thus preventing frequent changes in the port to which the frame is forwarded by the relay device. 【0012】 One aspect of this disclosure is a computer program for causing a computer to function as the relay device described above. By executing such a computer program, the same effects as those of the relay device described above can be obtained. 【0013】 One aspect of this disclosure is a relay method using the relay device described above. By implementing such a relay method, the same effects as those of the relay device described above can be obtained. 【0014】This is an explanatory diagram showing the configuration of a communication network. This is a block diagram showing the configuration of a relay device. This is a block diagram showing the functions of a relay device. Figure 4A is a flowchart showing the request processing in the first embodiment. Figure 4B is a flowchart showing the update processing in the first embodiment. Figure 5A is a flowchart showing the request processing in a modified example. Figure 5B is a flowchart showing the update processing in a modified example. 【0015】 Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings. 【0016】 [1. Overview] The relay device 1 of this embodiment functions as a so-called Ethernet® switch and is connected to communication terminals 2 (in other words, end stations, referring to the first and second communication terminals 2A and 2B in Figure 1) and other relay devices 1 (see Figures 1 to 3). The relay device 1 is configured to perform Ethernet communication with the communication terminals 2 connected to it and with the communication terminals 2 connected to other relay devices 1. 【0017】 Furthermore, the relay device 1 is configured to perform redundant communication via a redundant path compliant with IEEE (Institute of Electrical and Electronics Engineers) 802.1CB. Of course, the relay device 1 may not be limited to IEEE 802.1CB itself, but may also perform redundant communication compliant with a communication protocol similar to IEEE 802.1CB, specifically, for example, a communication protocol that is a revised version of IEEE 802.1CB or a communication protocol that references IEEE 802.1CB. As mentioned above, communication compliant with IEEE 802.1CB may include, for example, communication compliant with a communication protocol that is a revised version of IEEE 802.1CB or a communication protocol that references IEEE 802.1CB. 【0018】Furthermore, relay device 1 can be connected to multiple other relay devices 1 having a similar configuration to form multiple redundant paths. In Figure 1, as an example, multiple (four as an example) relay devices 1A to 1D are connected to form a ring network. Between the first communication terminal 2A connected to relay device 1A and the second communication terminal 2B connected to relay device 1C, redundant paths R1 (formed from relay devices 1A, 1B, and 1C) and R2 (formed from relay devices 1A, 1D, and 1C) are formed by the ring network. However, the relay devices 1 are not limited to this, and multiple relay devices 1 can be connected to form two or three or more redundant paths in various ways. Hereafter, when relay devices 1A to 1D are not distinguished, they will simply be referred to as relay device 1. 【0019】 Furthermore, the relay device 1 is configured, for example, for in-vehicle use, and is connected to other relay devices 1 mounted in the vehicle and to a communication terminal 2 which is an ECU (Electronic Control Unit). However, the relay device 1 is not limited to in-vehicle use and can be used for various purposes. Each relay device 1 may be a zone ECU, each located in a different area of ​​the vehicle. For example, relay device 1A may be located at the front of the vehicle, relay device 1B may be located on the right side of the vehicle, relay device 1C may be located on the left side of the vehicle, and relay device 1D may be located at the rear of the vehicle. Also, relay devices 1A, 1B, 1C, and 1D may be domain ECUs, each distinguished by domain. For example, relay device 1A may be a body ECU, relay device 1B may be a cockpit domain ECU, relay device 1C may be an ADAS (Advanced Driver Assistance System) domain ECU, and relay device 1D may be a powertrain domain ECU. In addition, a central ECU that integrates and manages the aforementioned domain ECUs may be mounted in the vehicle. Furthermore, the number of communication terminals connected to the relay device 1 is not limited to one; two or more communication terminals may be connected. 【0020】 [2. Configuration of the relay device] The relay device 1 comprises a control unit 10 and a plurality of ports 14 (see Figure 2). 【0021】 The control unit 10 comprises a CPU (Central Processing Unit) 10A and a memory 10B. The memory 10B includes RAM (Random Access Memory), ROM (Read Only Memory), and flash memory. The CPU 10A operates according to the relay program 10C stored in the memory 10B, executing processing for the overall control of the relay device 1. The memory 10B is configured as a non-transitional physical recording medium. 【0022】 In this embodiment, the functions and processing of the relay device 1 are, for example, realized by a CPU 10A operating according to the relay program 10C. However, the functions and processing of the relay device 1 are not limited to this, and may be realized by a CPU 10A operating according to the relay program 10C and an electronic circuit, or by an electronic circuit alone. 【0023】 Memory 10B stores Filtering Database 11 (hereafter referred to as FD11) and Transaction Port State 13 (hereafter referred to as TPS13). 【0024】 FD11 is a database equivalent to the Filtering Database defined in IEEE 802.1Q. FD11 records frame information and information indicating the destination port to which a frame containing that frame information should be forwarded when it is received. Specifically, frame information includes, for example, the destination MAC (Media Access Control) address and VID (VLAN ID) within the frame. 【0025】Furthermore, FD11 includes a MAC address table 12. The MAC address table 12 records the MAC address of the communication terminal 2 and port information indicating the port 14 to which a frame with that MAC address as the destination MAC address will be forwarded when such a frame is received. The port information is information for identifying each of the multiple ports 14 of the relay device 1, and is one example of a port bitmap. A port bitmap is a bit sequence in which each bit is associated with each port 14 of the relay device 1. The value of each bit in the bit sequence indicates whether or not the received frame will be forwarded from the port 14 of the relay device 1 corresponding to that bit. 【0026】 Figure 1 shows the MAC address table 12 of the relay device 1C to which the second communication terminal 2B is connected in this embodiment. In the MAC address table 12, "MAC A," which is the MAC address of the first communication terminal 2A, is associated with either "P1," which is the port to which the relay device 1B is connected, or "P2," which is the port to which the relay device 1D is connected. That is, the port corresponding to MAC A in the MAC address table 12 can change between P1 and P2. This is because multiple redundant paths R1 and R2 are formed between the first communication terminal 2A and the relay device 1C. Therefore, depending on the path taken by the frame transmitted from the first communication terminal 2A to reach the relay device 1C, the port corresponding to MAC A may change due to the learning process described later. In addition, in the MAC address table 12, "MAC B," which is the MAC address of the second communication terminal 2B, is associated with "P3," which is the port to which the second communication terminal 2B is connected. 【0027】Therefore, when the relay device 1C to which the second communication terminal 2B is connected receives a frame with MAC A as the destination MAC address from the second communication terminal 2B, the relay device 1C forwards the frame from port P1 to the relay device 1B, or from port P2 to the relay device 1D. Also, when the relay device 1C receives a frame with MAC B as the destination MAC address from the relay device 1B or the relay device 1D, the relay device 1C forwards the frame from port P3 to the second communication terminal 2B. 【0028】 TPS13 records the link status of each port 14 in accordance with IEEE 802.3. 【0029】 Port 14 is connected to another relay device 1 or communication terminal 2 via an Ethernet communication cable. 【0030】 Furthermore, the relay device 1 includes a frame transfer unit 15 and an arbitration unit 16, as functions realized by the CPU 10A executing a program (see Figure 3). 【0031】 The frame transfer unit 15 communicates via Ethernet with other relay devices 1 or communication terminals 2 connected to port 14. 【0032】 The arbitration unit 16 has the authority to write to and read from the FD 11. 【0033】 <Frame forwarding> The relay device 1 forwards frames in accordance with the Forwarding Process defined in IEEE 802.1Q (see Figures 1 to 3). 【0034】Specifically, when relay device 1 receives a frame from another relay device 1 or communication terminal 2 connected to port 14, frame transfer unit 15 extracts frame information from the frame. Then, frame transfer unit 15 requests arbitration unit 16 to search for FD 11 using the extracted frame information. In response to this request, arbitration unit 16 refers to FD 11, obtains information indicating the port 14 to output the frame when transferring the frame, and transmits it to frame transfer unit 15. Then, frame transfer unit 15 determines the port 14 to output the frame based on the received information. 【0035】 [3. Redundant Communication] In the ring network shown in Figure 1, as an example, when redundant communication is performed from the first communication terminal 2A to the second communication terminal 2B, two redundant paths R1 and R2 are formed by relay devices 1A to 1C and relay devices 1A, 1C, and 1D. Redundant communication will be explained below using Figure 1. 【0036】 When redundant communication is performed using redundant paths R1 and R2, the relay device 1 connected to the first communication terminal 2A receives a frame 4 from the first communication terminal 2A, adds a redundant tag (hereinafter, R-TAG) 30 to the frame 4, generates a redundant frame 3, and duplicates the redundant frame 3 (S100). 【0037】 Then, relay device 1 forwards redundant frames 3 to relay device 1 to which the second communication terminal 2B is connected, via redundant paths R1 and R2. Specifically, in redundant path R1, relay device 1 forwards redundant frames 3 to relay device 1C via relay device 1B. In redundant path R2, relay device 1 forwards redundant frames 3 to relay device 1C via relay device 1D. 【0038】 <Determination of First / Last Arrival> When the relay device 1C connected to the second communication terminal 2B receives a redundant frame 3, it determines whether or not the redundant frame 3 has not been received. 【0039】If the redundant frame 3 has not been received, it will be considered the first to arrive; if it has been received, it will be considered the second to arrive. If the redundant frame 3 is the first to arrive, the relay device 1C generates a frame 4 by removing the R-TAG 30 from the redundant frame 3 and forwards it to the second communication terminal 2B (S105). On the other hand, if the redundant frame 3 is the second to arrive, the relay device 1C discards the redundant frame 3 (S105). Alternatively, it may be determined whether the redundant frame 3 has not been received based on the sequence number contained in the redundant frame 3. Specifically, if the second communication terminal 2B has not received a redundant frame 3 having the same sequence number as the redundant frame 3 before receiving the redundant frame 3, it may be determined that the redundant frame 3 has not been received. In this case, the redundant frame 3 will be considered the first to arrive. On the other hand, if the second communication terminal 2B has received a redundant frame 3 having the same sequence number as the redundant frame 3 before receiving the redundant frame 3, it may determine that the redundant frame 3 has already been received. In this case, the redundant frame 3 will be considered to have arrived later. 【0040】 [4. Request Processing and Update Processing] The relay device 1 performs the request processing and update processing shown below. 【0041】 <Request Processing> Request processing is the process of requesting the execution of the learning process described later, and is executed by the frame transfer unit 15 when the relay device 1 receives a frame (including redundant frames 3). The request processing will be explained below using Figure 4A. 【0042】In S200, the frame transfer unit 15 acquires the value of the EtherType of the received frame (hereinafter referred to as the type value). Specifically, when the received frame does not include a VLAN tag, the frame transfer unit 15 acquires the EtherType value immediately following the source MAC address in the frame as the type value. On the other hand, when the received frame includes a VLAN tag, the frame transfer unit 15 acquires the EtherType value immediately following the VID (VLAN ID) included in the VLAN tag in the frame as the type value. Then, the frame transfer unit 15 proceeds to S205. 【0043】 In S205, the frame transfer unit 15 determines whether the received frame includes the R-TAG 30. Specifically, when the type value acquired in S200 is 0xF1C1, the frame transfer unit 15 determines that the R-TAG 30 is included, and when it is not 0xF1C1, the frame transfer unit 15 determines that the R-TAG 30 is not included. 【0044】 When the frame transfer unit 15 determines that the received frame includes the R-TAG 30 (S205: Yes), this process ends. On the other hand, when the frame transfer unit 15 determines that the received frame does not include the R-TAG 30 (S205: No), it proceeds to S210. 【0045】 In S210, the frame transfer unit 15 transmits a learning request to the arbitration unit 16. The learning request is a request to execute a learning process. The learning process is a process in which the arbitration unit 16 updates the MAC address table 12 (that is, registers a new MAC learning entry and overwrites an existing MAC learning entry), as will be described later. Then, the frame transfer unit 15 ends this process. 【0046】 <Update Process> The update process is a process for updating the MAC address table 12, and is executed by the arbitration unit 16 when the arbitration unit 16 receives a learning request from the frame transfer unit 15. Hereinafter, the update process will be described using FIG. 4B. 【0047】In S300, the arbitration unit 16 executes a learning process. Specifically, when there is no MAC learning entry including a MAC address that matches the source MAC address included in the received frame in the MAC address table 12, the arbitration unit 16 newly registers, as a MAC learning entry, the pair of the source MAC address of the frame and the port number on which the frame was received in the MAC address table 12. On the other hand, when there is a MAC learning entry including a MAC address that matches the source MAC address included in the received frame in the MAC address table 12, the arbitration unit 16 performs a process of overwriting the port information of the MAC learning entry with the port information indicating the port on which the frame was received. Then, the arbitration unit 16 ends this process. 【0048】 [5. Modification Example] In the above embodiment, in the request process in the frame transfer unit 15, it is determined whether or not the received frame includes an R-TAG 30. However, it is not limited to this. For example, in the update process in the arbitration unit 16, it may be determined whether or not the received frame includes an R-TAG 30. Specifically, the request process in the frame transfer unit 15 and the update process in the arbitration unit 16 may be as follows. 【0049】 <Request Process> The frame transfer unit 15 executes the request process shown in FIG. 5A. 【0050】 In S400, the frame transfer unit 15 obtains a type value from the received frame in the same manner as S200 in the above embodiment. Then, the frame transfer unit 15 proceeds to S405. 【0051】 In S405, the frame transfer unit 15 transmits, to the arbitration unit 16, a learning request similar to S210 and information indicating the type value obtained in S400. Then, the frame transfer unit 15 ends this process. 【0052】 <Update Process> The arbitration unit 16 executes the update process shown in FIG. 5B. 【0053】In S500, the arbitration unit 16 determines whether or not the received frame contains an R-TAG 30. Specifically, the arbitration unit 16 makes this determination based on the type value received from the frame transfer unit 15, similar to S205. 【0054】 If the arbitration unit 16 determines that the received frame contains an R-TAG 30 (S500: Yes), it terminates this process. On the other hand, if it determines that the received frame does not contain an R-TAG 30 (S500: No), it proceeds to S505. 【0055】 In S505, the frame transfer unit 15 performs the same learning process as in S300. Then, the arbitration unit 16 terminates this process. 【0056】 According to the embodiment described in detail above, the following effects can be obtained. 【0057】 [6. Effects] (1) When redundant communication in accordance with IEEE 802.1CB is performed multiple times from the first communication terminal 2A to the second communication terminal 2B, the redundant path traversed by the first arriving redundant frame 3 among the two redundant paths R1 and R2 may differ between each redundant communication. That is, the relay device 1 connected to the second communication terminal 2B may have different ports P1 and P2 that receive the first arriving redundant frame 3 between each redundant communication. 【0058】 As a result, the port associated with the MAC address of the first communication terminal 2A (i.e., MAC A) in the MAC address table 12 of the relay device 1 may frequently change between ports P1 and P2 due to the address learning function. Consequently, when the relay device 1 receives a frame with MAC A as the destination MAC address, the port to which the frame is forwarded may frequently change between ports P1 and P2. 【0059】On the other hand, according to the relay device 1 of this embodiment, if the frame received by the relay device 1 contains an R-TAG 30 (in other words, if the received frame is a redundant frame 3), the arbitration unit 16 does not perform the process of overwriting the MAC address table 12. Therefore, it is possible to suppress frequent changes in the port 14 that forwards frames in the relay device 1. 【0060】 [7. Correspondence between terms] In the above embodiment, the MAC address table 12 corresponds to the address table, the arbitration unit 16 corresponds to the update unit, and S205 and S500 correspond to the determination unit. 【0061】 [8. Other Embodiments] Although embodiments of the present disclosure have been described above, it goes without saying that the present disclosure is not limited to the embodiments described above and can take various forms. 【0062】 (1) In the above embodiment, the frame transfer unit 15 obtains the type value of the received frame in S200 and determines in S205 whether or not the frame contains an R-TAG 30 based on the type value, but is not limited to this. For example, the frame may contain information different from the type value mentioned above for determining whether or not an R-TAG 30 is included. Alternatively, the frame transfer unit 15 may obtain such information from the received frame and determine whether or not an R-TAG 30 is included based on that information. 【0063】 (2) In the above embodiment, two redundant paths R1 and R2 are formed by a plurality of relay devices 1 that constitute a ring network. However, the embodiment is not limited to this, and in the two redundant paths R1 and R2, relay devices other than the relay device 1 connected to the second communication terminal 2B may be conventional relay devices compliant with IEEE 802.1CB. 【0064】 Furthermore, a plurality of relay devices, including the relay device 1 of the above embodiment, may be used to form three or more redundant paths. In this case as well, the relay device 1 of the above embodiment is connected to the second communication terminal 2B, and the other in-vehicle devices may be the relay device 1 of the above embodiment or conventional relay devices. 【0065】 (3) The functions and processes of the relay device 1 described in this embodiment may be realized by a dedicated computer provided by configuring a processor and memory programmed to execute one or more functions embodied by a computer program. Alternatively, the functions and processes of the relay device 1 described in this embodiment may be realized by a dedicated computer provided by configuring a processor by one or more dedicated hardware logic circuits. Alternatively, the functions and processes of the relay device 1 described in this embodiment may be realized by one or more dedicated computers configured by a combination of a processor and memory programmed to execute one or more functions and a processor configured by one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by the computer on a computer-readable non-transitional tangible recording medium. The method for realizing the functions of each part included in the relay device 1 does not necessarily have to include software, and all of its functions may be realized using one or more hardware components. According to one aspect of this disclosure, a computer program product corresponding to the above-mentioned computer program may be provided. 【0066】 (4) Multiple functions of one component in the above embodiment may be realized by multiple components, or one function of one component may be realized by multiple components. Also, multiple functions of multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Furthermore, some of the configurations of the above embodiment may be omitted. Also, at least some of the configurations of the above embodiment may be added to or replaced with the configurations of other above embodiments. 【0067】(5) In addition to the relay device 1 described above, this disclosure can also be realized in various forms, such as a relay program 10C for causing a computer to function as the control unit 10 of the relay device 1, a non-transitional physical recording medium such as a semiconductor memory on which the relay program 10C is recorded, and a method realized by the relay program 10C. 【0068】 1, 1A to 1D... Relay device, 2, 2A, 2B... Communication terminal, 12... MAC address table, 14... Port, 15... Frame forwarding unit, 16... Arbitration unit, R1, R2... Redundant path.

Claims

1. A relay device (1) configured to perform communication in accordance with the IEEE (Institute of Electrical and Electronics Engineers) 802.1CB standard using Ethernet (registered trademark), comprising: a plurality of ports (14) for sending and receiving frames; an address table (12) associated with terminal information indicating a communication terminal (2) and port information indicating a port to which the frame is forwarded when the frame destined for the communication terminal is received; an update unit (16) configured to perform a learning process (S300, S505) when the frame is received, which is a process for overwriting the port information in the address table corresponding to the terminal information indicating the source of the frame with the port information indicating the port that received the frame; and a determination unit (S205, S500) configured to determine whether the received frame contains an R-TAG (30), wherein the update unit is configured not to perform the learning process corresponding to the reception of the frame if the determination unit determines that the received frame contains an R-TAG. Relay device.

2. A relay device according to claim 1, wherein the determination unit is configured to determine that the received frame contains the R-TAG when the value of the Ethernet Type of the received frame is 0xF1C1.

3. A relay device according to claim 1 or claim 2, further comprising: a Filtering Database (11) that conforms to the IEEE 802.1Q standard and includes the address table; and a frame forwarding unit (15), wherein the frame forwarding unit is configured to perform: a process of determining the port to which the received frame is forwarded based on the Filtering Database; and a process (S210) of sending a learning request to the update unit requesting the execution of the learning process (S300) when the frame is received; the update unit is configured to perform the learning process in response to the learning request sent from the frame forwarding unit; the frame forwarding unit comprises a determination unit (S205); and the frame forwarding unit does not send the learning request to the update unit in response to the reception of the frame if the determination unit determines that the received frame contains the R-TAG.

4. A relay device according to claim 2, further comprising: a Filtering Database including the address table, conforming to the IEEE 802.1Q standard; and a frame forwarding unit, wherein the frame forwarding unit is configured to perform: a process of determining the port to which the received frame is forwarded based on the Filtering Database; and a process (S405) of transmitting to the update unit, upon receiving the frame, information indicating the value of the Ethernet Type of the frame and a learning request requesting the execution of the learning process (S505); the update unit comprises a determination unit (S500); and the update unit, if the determination unit determines that the received frame does not contain the R-TAG, performs the learning process in accordance with the learning request transmitted in response to the reception of the frame; and if the determination unit determines that the received frame contains the R-TAG, does not perform the learning process in accordance with the learning request transmitted in response to the reception of the frame. Relay device.

5. A computer program (10C) for causing a computer in a relay device (1) configured to perform communication in accordance with the IEEE (Institute of Electrical and Electronics Engineers) 802.1CB standard using Ethernet (registered trademark) to execute processing, wherein the relay device comprises a plurality of ports (14) for sending and receiving frames, an address table (12) associated with terminal information indicating a communication terminal (2) and port information indicating the port to which the frame is forwarded when the frame destined for the communication terminal is received, and the processing includes, when the frame is received in the relay device, overwriting the port information in the address table corresponding to the terminal information indicating the source of the frame with the port information indicating the port to which the frame was received, and determining whether the received frame contains an R-TAG (30), and the overwriting includes, if it is determined that the received frame contains an R-TAG, not overwriting the port information corresponding to the reception of the frame.

6. A relay method using a relay device (1) configured to perform communication in accordance with the IEEE (Institute of Electrical and Electronics Engineers) 802.1CB standard using Ethernet (registered trademark), wherein the relay device comprises a plurality of ports (14) for sending and receiving frames, an address table (12) associated with terminal information indicating a communication terminal (2) and port information indicating the port to which the frame is forwarded when the frame destined for the communication terminal is received, the relay method includes, when the relay device receives the frame, overwriting the port information in the address table corresponding to the terminal information indicating the source of the frame with the port information indicating the port that received the frame, and determining whether the received frame contains an R-TAG (30), wherein the overwriting includes not overwriting the port information in response to the reception of the frame if it is determined that the received frame contains an R-TAG.

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