Configuration Guide Vol. 1

27.7 Notes on using Ring Protocol

<Structure of this section>

(1) Configuration changes during operation

When changing the configuration of a Ring Protocol during operation, care must be taken to avoid looping. The following shows how to handle the target configuration.

Changing the control VLAN (configuration command control-vlan) and the data-transfer VLAN (configuration command axrp vlan-mapping,vlan-group)

When changing the control VLAN or data transfer VLAN to be used in the ring, a loop occurs on the network. Therefore, stop VLAN to be changed in advance, or make the ring port down with a shutdown command. Then, change it.

(2) Coexistence with other functions

[See "22.3 Coexistence of Layer 2 switch function and other functions"

(3) VLAN for Sending and Receiving Control Frames

(4) About Ring VLAN Status of Transit Node

For transit nodes, when a fault occurs for a device or ring port, and recovery succeeds, the ring VLAN status of the ring port is set to Blocking to prevent loops from occurring. One of the ways in which this Blocking status is cleared is when the reception hold time (forwarding-shift-time) for flush control frames times out. If the flush control frame receive hold time (forwarding-shift-time) is shorter than the master node's health check send interval, the transit node's ring port may enter the forwarding state before the master node detects the recovery of the ring failure and changes the secondary port to the blocking state, which may cause a loop. Therefore, set the flush control frame receive hold time (forwarding-shift-time) to a value greater than the master node's health check send interval.

(5) About networking when using Ring Protocol

Networks using the Ring Protocol have looped configurations. Therefore, build such networks as follows to avoid loops.

  1. Beforehand, use shutdown or another command to take the ring port (physical port or channel group) of the ring configuration node down.

  2. Set the Ring Protocol configuration, or copy (copy command) the configuration file including the Ring Protocol settings, to enable the Ring Protocol.

  3. Bring the ring port back up (such as by clearing the shutdown command) when the Ring Protocol is set for all devices in the network.

(6) Interoperability

Ring Protocol is our proprietary feature. It cannot be used interoperably with third-party switches.

(7) Multiple Failures in a Network

When multiple faults occur between different nodes in the same ring (a multi-fault), because the master node was already performing fault detection for the first fault, the second and subsequent faults are not detected. Also, because health check frames sent by the master node cannot be received until recovery from the last fault in a multi-fault restoration detection situation occurs, recovery cannot be detected. As a result, communication might be temporarily impossible for multi-faults when a partial fault is restored (when a fault remains for the ring).

Note that when the multi-fault monitoring functionality is applied, multi-faults might be able to be detected, depending on the combination of faults. For information about the multiple failure monitoring feature, see Multiple Failure Monitoring Feature in 27.5 Ring Protocol.

(8) Configuration Commands with VLAN Down Settings

If no configuration commands pertaining to the Ring Protocol have been set, when the first configuration command pertaining to the Ring Protocol (one of the following commands) is set, all VLANs will go down temporarily. Therefore, when a ring network that uses the Ring Protocol is built, we recommend setting the following configuration commands ahead of time.

Note that for VLAN mapping (the axrp vlan-mapping command), the VLANs associated with the VLAN mapping will go down temporarily, even for new settings. The VLAN mappings already set and the other VLANs to which they are associated are not affected.

(9) Transmission/reception of flush control frames at master node startup

When the master node device restarts, and the transit node detects link-up for the ring port connected to the master node later than the master node does, the transit node might not be able to receive the flush control frames sent by the master node during initial operation. Here, the status of the ring port for the transit node unable to receive flush control frames will be Blocking. The corresponding ring port changes to the Forwarding status and communication is restored after the reception hold time for flush control frames (forwarding-shift-time) elapses.

When flush control frames cannot be received on neighboring transit nodes, and the sending count for flush control frames from the master node is controlled, reception might be possible. Also, to shorten the time to cut communication due to flush control frames not yet received, shorten the reception hold time for flush control frames sent by the transit node (initial value: 10 seconds).

The same applies when the following operations are performed on the master node:

(10) About the monitoring start timing of the multiple failure monitoring function

After the multi-fault monitoring functionality is applied to a shared node, multi-fault monitoring is started when the first multi-fault monitoring frame sent from the opposing shared node is received. As such, when the multi-fault monitoring functionality is set and a fault occurs for a ring network, multi-fault monitoring cannot be started. Set the multi-fault monitoring functionality when the status of the ring network is normal.

(11) Communication during partial recovery from multiple failures

Because the master node does not detect ring restoration during partial multi-fault recovery, the transit node ring port is logically blocked until the reception hold time (forwarding-shift-time) for flush control frames elapses. To clear the logical block status, either shorten the reception hold time for flush control frames (initial value: 10 seconds), or recover remaining link faults to have the master node detect ring restoration. When setting the receive wait protection time for a flush control frame, set a value larger than the transmission interval for multiple failure monitoring frames on the shared node. When a small value is set, loops might occur temporarily.

(12) Down link aggregation specified for a ring port

When nodes in a ring network are connected via link aggregation (static mode or LACP mode), make sure to shut down all physical ports belonging to the channel group by using the shutdown command before shutting down the channel group of the link aggregation by using the shutdown command.

If you bring up the channel group using the no shutdown command, make sure to shut down all physical ports belonging to the channel group by using the shutdown command.

(13) Executing restart Commands

If the following operation command is executed on a transit node, the ring port VLAN goes down, so the master node erroneously detects a ring failure and forwards the secondary port. Because the ring port of the transit node is in a transient down state, a loop occurs until the master node detects the recovery of the ring failure.

When executing these commands on a transit node, perform the following steps to prevent loops:

  1. Use shutdown command to set the ring port to the down status.

  2. Run the above restart commandI will do it.

  3. In step 1, set the ring port in the down state to the up state (release shutdown command, etc.).

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