JP5812934B2 - Communication system and communication control method - Google Patents

Description

  The present invention relates to a communication system to which multi-chassis link aggregation and ERP (Ethernet (registered trademark) Ring Protection) are simultaneously applied.

  Link aggregation is standardized by the Institute of Electrical and Electronic Engineers (IEEE) for the purpose of bandwidth expansion, load distribution, and route redundancy in a layer 2 network composed of layer 2 switches.

  Link aggregation is a technique for extending a band by virtually allocating a plurality of links between layer 2 switches to a LAG (Link Aggregation Group) and treating them as a single link. Further, it is possible to distribute the traffic load by distributing the traffic to a plurality of links belonging to the LAG. Furthermore, it is possible to realize a path redundancy function in which communication is continued by disconnecting the faulty link from the LAG and not allocating traffic to the faulty link (see Non-Patent Document 1).

  Multi-chassis link aggregation is an extension technology of link aggregation. In multi-chassis link aggregation, link failure information is shared between two adjacent layer 2 switches, the layer 2 switch is treated logically as one layer 2 switch, and the link of any layer 2 switch belongs to the LAG. Can be handled as a single link.

  ERP is a loop prevention and redundancy technique in a layer 2 ring network. In ERP, a logical network loop is prevented by generating a blocking port that does not conduct traffic in a layer 2 switch constituting a layer 2 ring network. In addition, neighbor layer 2 switch health monitoring using a dedicated frame called Ethernet (registered trademark) OAM (Operation, Administration, and Maintenance) and simple blocking port operation utilizing the ring topology makes it as short as 50 mm when a failure occurs. It is possible to switch the route of the layer 2 ring network in seconds. A redundant function is realized by this path switching (see Non-Patent Document 2).

“IEEE Std 802.3-2002, Section Three”, 3/2002 ITU-T recommendation 8032 / Y. 1744, “Ethernet Ring Protection Switching”, 2008

  However, in a network to which multi-chassis link aggregation and ERP are applied at the same time, there is a problem that load distribution by multi-chassis link aggregation becomes impossible when a failure occurs at a specific location in the network. In addition, when a double failure occurs, there is a problem that the frame is discarded in the layer 2 switch on the route to the destination device, and the frame may not reach the destination device.

  The present invention has been made in view of the above, and an object of the present invention is to provide a communication system and a communication control method capable of enhancing fault tolerance in a network to which multi-chassis link aggregation and ERP are simultaneously applied.

  In order to solve the above-mentioned problems and achieve the object, the present invention includes a plurality of ring networks formed by a plurality of switch devices, each ring network is applied with ERP, and each ring network includes two units. A communication system that is connected to another ring network by a switch device and the boundary switch device, which is the two switch devices, constitutes multi-chassis link aggregation, and in each ring network, between the boundary switch devices A normal path that is the shortest path, and a detour path that indicates a path different from the normal path, and each boundary switch device monitors the occurrence of a failure in each of the normal path and the detour path, and When there is no failure in the path, transfer to another ring network When a frame to be received is received from a switch device other than another boundary switch device, the received frame is transferred to the link with the other ring network or the normal path, and in a state where a failure occurs in the normal path When a frame to be transferred to another ring network is received from a switch device other than another boundary switch device, the received frame is transferred to a link with the other ring network or the bypass path.

  According to the present invention, in a communication system applying multi-chassis link aggregation and ERP, even if a failure occurs in a link (normal path) between switch devices constituting the multi-chassis link aggregation, the multi-chassis link The traffic load distribution by aggregation can be continued, and the communication system with improved fault tolerance can be realized.

FIG. 1 is a diagram illustrating a configuration example of a communication system according to the first embodiment. FIG. 2 is a diagram illustrating an operation example in a conventional communication system. FIG. 3 is a diagram illustrating an example of a communication failure. FIG. 4 is a diagram illustrating an example of a control procedure for realizing multi-chassis link aggregation in the communication system according to the first embodiment. FIG. 5 is a diagram illustrating an example of path setting control for multi-chassis link aggregation. FIG. 6 is a diagram illustrating an example of a communication failure. FIG. 7 is a diagram illustrating an example of a control procedure for realizing multi-chassis link aggregation in the communication system according to the second embodiment. FIG. 8 is a diagram illustrating an example of path setting control for multi-chassis link aggregation.

  Embodiments of a communication system and a communication control method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a communication system according to the first embodiment. As shown in FIG. 1, in the present embodiment, a communication system including layer 2 switches (hereinafter referred to as L2 switches) 101 to 106 and 111 to 116 is assumed. Each L2 switch is assumed to be equipped with ERP.

  The L2 switches 101 to 106 form a layer 2 ring network (hereinafter referred to as a ring network) 100, and the L2 switches 111 to 116 form a ring network 110. The ring networks 100 and 110 are connected by a link 121 between the L2 switches 103 and 111 and a link 122 between the L2 switches 106 and 114. A communication terminal 131 is connected to the L2 switch 104 of the ring network 100, and a communication terminal 132 is connected to the L2 switch 113 of the ring network 110. Communication terminals 131 and 132 communicate with each other by transmitting and receiving Ethernet frames (hereinafter referred to as frames) via ring networks 100 and 110. In the L2 switches 104 and 113, ERP blocking ports (hereinafter referred to as blocking ports) are set. Specifically, the L2 switch 104 blocks a port to which a physical link with the L2 switch 105 is connected. The L2 switch 113 blocks a port to which a physical link with the L2 switch 116 is connected. A frame transmitted from the communication terminal does not pass through the blocking port. In FIG. 1, the link between the L2 switches 104 and 105 and the link between the L2 switches 113 and 116 are indicated by broken lines as logically unconnected physical links (physical links that do not allow frames to pass).

  The L2 switches 103 and 106 that operate as boundary switch devices in the ring network 100 implement multi-chassis link aggregation, and share link failure information for multi-chassis link aggregation. Similarly, the L2 switches 111 and 114 as boundary switch devices in the ring network 110 implement multi-chassis link aggregation, and share link failure information for multi-chassis link aggregation. The L2 switch 103 and the L2 switch 111 are connected by a physical link 121, and the L2 switch 106 and the L2 switch 114 are connected by a physical link 122. In the communication system shown in FIG. 1, the L2 switches 103 and 106 in which multi-chassis link aggregation is implemented are virtually treated as one L2 switch.

  An ERP adjacency monitoring frame (Ethernet OAM Continuity Check) is transmitted and received between the L2 switches. When the L2 switch does not receive the ERP adjacency monitoring frame for a certain period of time, it determines that a failure has occurred in the adjacent L2 switch or the physical link connecting itself to the adjacent L2 switch.

  Here, the operation of a conventional communication system to which multi-chassis link aggregation and ERP are applied, and problems to be solved by the invention according to the present embodiment will be described. The case where the communication terminal 131 transmits a frame addressed to the communication terminal 132 assuming the system configuration shown in FIG.

  The network administrator sets link aggregation in advance. In the case of the configuration of FIG. 1, first, the L2 switch 103 is set to create a certain LAG, and then the physical links 121 and 122 are set to belong to the created LAG. Link aggregation is set for the L2 switches 111 and 114 in the same manner.

  When the communication terminal 131 transmits a frame addressed to the communication terminal 132, the frame transfer is as shown in FIG. FIG. 2 is a diagram illustrating an operation example in the communication system, and illustrates an operation when the communication terminal 131 transmits a frame to the communication terminal 132.

  As shown in FIG. 2, the frame addressed to the communication terminal 132 transmitted by the communication terminal 131 reaches the L2 switch 103 via the L2 switches 104, 101 and 102. The L2 switch 103 searches its own frame transfer table (the frame transfer table illustrated in the lower left of FIG. 2) using the destination MAC address of the received frame addressed to the communication terminal 132 as a key, and confirms the output destination link. . In the illustrated example, the output link is found to be LAG1 as a result of the search. When the output link is LAG1 (link aggregation group), the L2 switch 103 further searches its own link aggregation table (link aggregation table having the contents illustrated in the lower right in FIG. 2) using the output link LAG1 as a key. Confirm the link belonging to LAG1. In the illustrated example, as a result of the search, it is found that the belonging links of LAG1 are the physical links 121 and 122. When the belonging link is determined, the L2 switch 103 selects one of the physical links 121 and 122 as a final output link of the frame by a predetermined load distribution method. One of the load balancing methods is round robin. In round robin, frames are alternately output from physical links 121 and 122 (each time the output link receives a frame of LAG1, the physical links 121 and 122 are alternately selected as the final output link). As another method, a frame is output based on an output value obtained by inputting specific field values such as a destination IP address, a source IP address, and a destination port number in a frame into a function called a hash function. There is a way to determine the physical link.

  The L2 switch 111 that has received the frame via the physical link 121 and the L2 switch 114 that has received the frame via the physical link 122 operate virtually as one L2 switch by multi-chassis link aggregation. The physical links 121 and 122 are handled as one link, and the output destinations of frames received through these physical links are determined by the L2 switches 111 and 114 using the destination MAC address as a key. The frame addressed to the communication terminal 132 reaches the communication terminal 132 via the L2 switches 112 and 113.

  In a conventional communication system that transfers a frame transmitted from a communication terminal in such a procedure, if a failure occurs between two L2 switches constituting a multi-chassis link aggregation, traffic load distribution cannot be continued. There are challenges. This problem will be described with reference to FIG.

  When the failure illustrated in FIG. 3, that is, a failure occurs in the physical link 301 between the L2 switches 103 and 106, the L2 switch 103 cannot receive the ERP adjacency monitoring frame transmitted by the L2 switch 106. For this reason, the L2 switch 103 determines that a failure has occurred in the physical link 301 or the L2 switch 106. Similarly, the L2 switch 106 determines that a failure has occurred in the physical link 301 or the L2 switch 106. As a result, the L2 switches 103 and 106 generate a blocking port in the physical link 301. Further, the L2 switches 103 and 106 transmit an ERP control frame (R-APS frame) indicating that a failure has been detected. The L2 switch 104 that has received this ERP control frame releases the port blocking. With the above operation, the conventional communication system realizes path switching and loop prevention when a failure occurs.

  However, when a failure occurs in the physical link 301, link failure information for realizing multi-chassis link aggregation cannot be transmitted / received between the L2 switches 103 and 106, and link failure information necessary for aggregation cannot be shared. . Therefore, the physical link 122 is deleted from the output link destination (affiliation link) in the link aggregation table of the L2 switch 103. As a result, the L2 switch 103 that has received the frame addressed to the communication terminal 132 selects only the physical link 121 as the output link destination and cannot maintain the traffic load distribution.

  In order to solve such a problem, in the communication system according to the present embodiment, the following control is executed, and physical between L2 switches operating virtually as one L2 switch by multi-chassis link aggregation. Even if a failure occurs on the link, the load distribution of traffic is continued.

  FIG. 4 is a diagram illustrating an example of a control procedure for realizing multi-chassis link aggregation in the communication system according to the first embodiment.

  As shown in FIG. 4, in the communication system of the present embodiment, as main control for realizing multi-chassis link aggregation, step S11 for generating a detour path and multi-chassis link aggregation using the detour path Step S12 for confirming each other's normality (that is, the normality of the bypass path) between the L2 switches constituting the normal path (generated on the physical link between the two L2 switches constituting the multi-chassis link aggregation) When the failure of the logical link is detected, step S13 is performed to transmit / receive information (link failure information) necessary for load distribution and to transmit a frame by using a bypass path. Details of these steps will be described below with reference to FIG. FIG. 5 is a diagram illustrating an example of path setting control for multi-chassis link aggregation in the communication system illustrated in FIG. 1.

  First, step S11 will be described. The L2 switches 103 and 106 realizing multi-chassis link aggregation generate a path for transmitting / receiving link failure information on the physical link 301 that directly connects each other (normal path). Further, the L2 switch 103 generates a detour path 601 different from the normal path 602 for the pair of L2 switches 106 constituting the multi-chassis link aggregation. Specifically, a path that reaches the L2 switch 106 via the L2 switches 102, 101, 104, and 105 is generated as a bypass path 601. Note that the generation method of the bypass path 601 is not limited here. For example, a method for generating a detour path using L2TP (Layer 2 Tunneling Protocol) after the user statically sets information on a pair of L2 switches (L2 switch 106) in the L2 switch (L2 switch 103) in advance. Is used.

  Next, step S12 will be described. When the L2 switch 103 executes step S11 to generate the bypass path 601, the L2 switch 103 periodically monitors the normality of the bypass path 601. In other words, in order to confirm the normality of the L2 switch 106 and the bypass path 601 with respect to the paired L2 switch 106 using the bypass path 601, an operation of periodically transmitting a control frame is started. Similarly, the pair of L2 switches 106 periodically transmit control frames to the pair of L2 switches 103. The L2 switches 103 and 106 determine that the bypass path 601 and the pair of L2 switches are normal when receiving the control frame (control frame for normality confirmation) transmitted from the pair of L2 switches from the bypass path 601. . If the control frame for normality confirmation cannot be received for a certain period, it is determined that a failure has occurred in the detour path 601 or the paired L2 switch. The operation for confirming the normality of the bypass path 601 (and the paired L2 switch) is the operation for confirming the normality of the normal path 602 (path generated on the physical link between the L2 switches 103 and 106). That is, only the transmission path (path) of the control frame for normality confirmation is different. The L2 switches 103 and 106 that perform multi-chassis link aggregation periodically transmit normality confirmation control frames to both the normal path 602 and the bypass path 601 to confirm the normality of both paths. Note that the cycle for transmitting the normality confirmation control frame to the normal path 602 and the cycle for transmitting the normality confirmation control frame to the bypass path 601 may be different.

  Finally, step S13 will be described. When it is determined that a failure has occurred in the normal path 602, the L2 switch 103 uses the detour path 601 instead of the normal path 602 until the failure is recovered, and loads between the pair of L2 switches 106. Send and receive information (link failure information) necessary for distribution. When a frame to be transferred to the ring network 110 side, such as a frame addressed to the communication terminal 132, is received, the frame to be transferred to the ring network 110 side is transmitted to the physical link 122 via the physical link 122 using the bypass path 601. To do. Although the operation of the L2 switch 103 has been described here, the operation when the L2 switch 106 detects the occurrence of a failure in the normal path 602 is the same.

  Although the details are omitted, when a failure is detected, the L2 switch changes the setting of the blocking port according to the ERP. When a failure occurs in the normal path 602, as shown in FIG. 3, the L2 switches 103 and 106 that have detected this failure set the port connected to the physical link 301 in which the failure has occurred as a blocking port. In addition, other L2 switches are notified that a failure has occurred. Upon receiving this notification, the L2 switch updates the held frame transfer table as necessary. In addition, the L2 switch that is blocking the port for loop prevention releases the port block.

  In addition, when the L2 switch configuring the multi-chassis link aggregation receives a frame to be transferred to another ring network from the paired L2 switch via the normal path 602 or the bypass path 601, the received frame is transmitted to itself. The data is output to a path set on a physical link (physical link 121 or 122) connected to another ring network and transferred to another ring network. For example, when the frame addressed to the communication terminal 132 is received via the normal path 602 or the bypass path 601, the L2 switch 106 outputs the frame to a path set on the physical link 122.

  In addition, although the control procedure when a failure occurs in a state where the communication terminals 131 and 132 are connected to the L2 switches 104 and 113 for which the blocking port is set has been described, the L2 switch for which the blocking port is not set has been described. The control procedure when the communication terminal is connected is the same.

  As described above, in the communication system according to the present embodiment, a path (normal path) and a detour path on a physical link that directly connects these L2 switches are set between a pair of L2 switches that form a multi-chassis link aggregation. These L2 switches monitor the normality of the normal path and detour path, and when a failure is detected in the normal path, the detour path is used to transmit / receive link fault information necessary for load distribution and load distribution (Traffic distribution). As a result, when multi-chassis link aggregation and ERP are applied, even if a failure occurs in the link (normal path) between the L2 switches that make up multi-chassis link aggregation, traffic load due to multi-chassis link aggregation Dispersion can be continued and fault tolerance can be increased.

Embodiment 2. FIG.
In the first embodiment described above, the control for solving the problem that load distribution cannot be continued when a failure occurs in a physical link between L2 switches that implement multi-chassis link aggregation has been described. If a failure occurs after the control of the first embodiment, the following problem occurs.

  That is, after the path switching in the first embodiment was performed in accordance with the occurrence of a failure in the physical link between the L2 switches 103 and 106 in which multi-chassis link aggregation is implemented, a failure occurred in another L2 switch. In this case (when a double failure occurs), frame discard occurs.

  This problem will be described with reference to FIG. In FIG. 6, although a failure has occurred in the physical link 301 between the L2 switches 103 and 106, the control described in the first embodiment is executed, and the L2 switch 103 transfers the frame addressed to the communication terminal 132 to the physical link 121. And 122, an example in the case where a failure further occurs while the traffic load is distributed is shown. FIG. 6 shows a case where a new failure has occurred in the L2 switch 105 as an example. When the L2 switch 103 decides to transfer the frame addressed to the communication terminal 132 from the physical link 122 to the ring network 110 in a state before a new failure occurs, the L2 switch 103 transfers the frame addressed to the communication terminal 132 to the L2 switch 102. This frame reaches the physical link 122 via the L2 switches 102, 101, 104, 105 and 106. However, when a failure occurs in the L2 switch 105 in this state, the frame addressed to the communication terminal 132 cannot reach the physical link 122, and the frame is discarded in the L2 switch 105 in which the failure has occurred.

  In order to solve such a problem, in the communication system of the present embodiment, the following control is executed to avoid the occurrence of frame discard when a double failure occurs.

  FIG. 7 is a diagram illustrating an example of a control procedure for realizing multi-chassis link aggregation in the communication system according to the second embodiment.

  As shown in FIG. 7, in the communication system of the present embodiment, as the main control for realizing the multi-chassis link aggregation, step S21 for detecting multiple failures due to the control frame failure of the detour path, and link aggregation Step S22 for deleting a physical link belonging to the paired L2 switch from the table, Step S23 for instructing link aggregation opposite L2 switch (opposite L2 switch on the other ring network side) to release link aggregation (LA), The L2 switch that has received the LA release instruction executes step S24 in which the physical link corresponding to the LA release instruction is deleted from the link aggregation table. Details of these steps will be described below with reference to FIG.

  FIG. 8 is a diagram illustrating an example of path setting control for multi-chassis link aggregation in the communication system illustrated in FIG. 1. FIG. 8 shows a state in which the bypass path 601 is used by executing the control described in the first embodiment when a failure occurs in the physical link 301 between the L2 switches 103 and 106 constituting the multi-chassis link aggregation. FIG. 4 shows a case where the L2 switch (L2 switch 105 in the illustrated example) forming the detour path 601 has failed.

  First, step S21 will be described. The L2 switch 103 determines that a failure has occurred in the bypass path 601 when no control frame is received for a certain period of time when a control frame is transmitted and received using the bypass path 601, and a normal path failure (bypass) A multiple failure (double failure) is detected together with a failure that causes the use of the path 601 to start.

  Next, step S22 will be described. After detecting multiple failures, the L2 switch 103 deletes the physical link 122 between the paired L2 switch 106 and the ring network 110 from the held link aggregation table. As a result, the physical link 122 is not selected as the output link of the frame addressed to the communication terminal 132, so that no frame discard occurs. That is, since the physical link 121 is always selected as the output destination (output link) of the frame addressed to the communication terminal (for example, the communication terminal 132) on the ring network 110 side, the frame is sent to the L2 switch 105 where the failure has occurred. Are not transferred, and the frame is not discarded by the L2 switch 105.

  Next, step S23 will be described. The L2 switch 103 instructs the L2 switch 111 that is a link aggregation facing L2 switch to cancel the link aggregation.

  Finally, step S24 will be described. Receiving the link aggregation cancellation instruction, the L2 switch 111 deletes the physical link 122 between the L2 switch 114 and the ring network 100 as its pair from the held link aggregation table. As a result of this processing, the physical link 122 is not selected as the output destination link of the frame to be transferred from the ring network 110 to the ring network 100 (for example, the frame addressed to the communication terminal 131 transmitted from the communication terminal 132), and thus a failure occurs. The frame is not discarded by the L2 switch 105 being used.

  As described above, in the communication system according to the present embodiment, when the L2 switch configuring the multi-chassis link aggregation detects a failure in the bypass path in a state where load sharing is performed using the bypass path, The path setting for multi-chassis link aggregation is canceled by deleting the physical link between the paired L2 switch and the other ring network from the link aggregation table, and for the opposite L2 switch on the other ring network side It was decided to instruct to cancel the route setting for multi-chassis link aggregation. In addition, when the opposite L2 switch on the other ring network side is instructed to cancel the route setting for multi-chassis link aggregation, the physical link between the paired L2 switch and the other ring network is deleted from the link aggregation table. Therefore, the route setting for multi-chassis link aggregation is canceled. Thereby, although load distribution cannot be continued, the possibility that a frame is discarded by the L2 switch in which a failure has occurred can be reduced, and communication can be maintained.

  In the first and second embodiments, the operation when the L2 switch configuring the multi-chassis link aggregation detects a failure has been described. However, when the detected failure is recovered, the setting is restored to the original setting. Return to the operation before failure detection. For example, when one of the faults is recovered in the state shown in FIG. 8 (a state where a double fault has occurred), the L2 switch establishes a physical link between the paired L2 switch and the other ring network. , Re-register with the link to which the link aggregation table is held. Further, the link aggregation reconfiguration is instructed to the link aggregation facing L2 switch. Receiving the reconfiguration instruction, the L2 switch re-registers the physical link between the paired L2 switch and another ring network in the link to which the link aggregation table is held. Thereby, load distribution by multi-chassis link aggregation can be resumed.

  Moreover, although the communication system comprised including two layer 2 ring networks was demonstrated, it is good also as a structure containing three or more layer 2 ring networks.

  As described above, the communication system according to the present invention is useful as a communication system including a ring network including layer 2 switches in which ERP and multi-chassis link aggregation are implemented.

100, 110 Layer 2 ring network 101-106, 111-116 L2 switch 121, 122, 301 Physical link 131, 132 Communication terminal 601 Alternate path 602 Normal path

Claims (4)

A plurality of ring networks formed by a plurality of switch devices are provided, ERP is applied to each ring network, and each ring network is connected to another ring network by two switch devices. A communication system in which a certain boundary switch device constitutes multi-chassis link aggregation,
In each ring network, a normal path that is the shortest path and a detour path that indicates a path different from the normal path are set between the boundary switch devices.
Each boundary switch device monitors whether or not a failure has occurred in each of the normal path and the detour path, and in a state where no failure has occurred in the normal path, a frame to be transferred to another ring network When received from a switch device other than the border switch device, the received frame is transferred to the link with the other ring network or the normal path, and in a state where a failure occurs in the normal path, the other ring network When a frame to be transferred to the network is received from a switch device other than the other boundary switch device, the received frame is transferred to a link with the other ring network or the bypass path.   When the boundary switch device detects that a failure has occurred in both the normal path and the bypass path, it cancels the setting of multi-chassis link aggregation, thereby transferring a frame to be transferred to another ring network. If received, set the frame to always be transferred to the link with the other ring network, and further instruct the switch device connected by the link to cancel the multi-chassis link aggregation setting. The communication system according to claim 1. A plurality of ring networks formed by a plurality of switch devices are provided, ERP is applied to each ring network, and each ring network is connected to another ring network by two switch devices. A communication control method executed by a communication system in which a certain boundary switch device constitutes multi-chassis link aggregation,
In each ring network, a path setting step for setting a normal path that is the shortest path between each boundary switch device and a detour path that indicates a path different from the normal path;
Each boundary switch device monitors whether or not a failure has occurred in each of the normal path and the detour path, and in a state where no failure has occurred in the normal path, a frame to be transferred to another ring network When received from a switch device other than the border switch device, the received frame is transferred to the link with the other ring network or the normal path, and in a state where a failure occurs in the normal path, the other ring network A frame transfer step for transferring the received frame to a link with the other ring network or the detour path when a frame to be transferred to the network is received from a switch device other than the other boundary switch device;
The communication control method characterized by including. When the boundary switch device detects that a failure has occurred in both the normal path and the bypass path, the frame to be transferred to another ring network is released by canceling the multi-chassis link aggregation setting. If received, set the frame to always be transferred to the link with the other ring network, and further instruct the switch device connected by the link to cancel the multi-chassis link aggregation setting. Setting change step,
The communication control method according to claim 3, further comprising:

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