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20 Description of the Ring Protocol
frames is used to restrict the range for sending control frames. These VLANs are called
control VLANs, and the same VLAN is used for all nodes constituting a ring. Because
control VLANs use a single common VLAN for each ring, in a multi-ring configuration,
different VLANs need to be used in neighboring rings.
20.2.3 Fault monitoring methods
Ring faults are monitored under the Ring Protocol by the master node. For details, see the
manuals that describe master nodes.
20.2.4 Switching communication paths
When a ring fault is detected by the master node, a control frame called a flush control
frame is sent to the transit nodes that have the same control VLAN to request that MAC
address table entries be cleared. When a Switch, as a transit node, receives this flush
control frame, it clears MAC address table entries for the ring port. Because of this, flooding
occurs until MAC address learning is performed. MAC address learning is performed by
sending and receiving frames on the new path, and communication path switching is
completed.
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