When you have other nonparticipating switches in the ring, you can use the IEEE 802.1ag support to perform link health checks to the next ERN.
With IEEE 802.1ag configured, the ERNs within the ring send Continuity Check Messages (CCM) to verify the integrity of their own links. If a node is not receiving CCMs or if a link goes down, a failure is reported to the ring through R-APS messages.
The following figure shows a segment with ERNs 3 and 4 and two non-participating switches located on the same network segment between them. When ERNs 3 and 4 stopped receiving CCMs, the following actions occurred on ERNs 3 and 4:
