Allied Telesis AT-8700XL, RAPIER I, X900-48FE, AT-8900, AT-9900, AT-8600 Fault Recovery Procedure

Ethernet Protection Switching Ring (EPSR) 5

Fault Recovery Procedure

When the master node detects an outage somewhere in the ring, using either of the detection methods previously described, it will:

■declare the ring to be in a “failed” state

■unblock its secondary port to enable the data VLAN traffic to pass between its primary and secondary ports.

■flush its own forwarding database (FDB) for (only) the two ring ports

■send an EPSR “Ring-Down-Flush-FDB” control message to all the transit nodes, via both its primary and secondary ports

The transit nodes respond to the “Ring-Down-Flush-FDB” message by flushing their forward databases for each of their ring ports. As the data starts to flow in in the ring’s new configuration, each of the nodes (master and transit) re-learn their layer 2 addresses. During this period, the master node continues to send health check messages over the control VLAN. This situation continues until the faulty link or node is repaired. Figure 1-2shows the flow of control frames under fault conditions.

Figure 1-2: EPSR Fault Detection Messages

Control VLAN “forwarding”			Control Vlan “forwarding”
Data VLANs
			Data VLANs “forwarding”
“move from blocking to forwarding”
	S	P
		Master
	Transit	Node	Transit
	Node		Node
	4		1
	Transit		Transit
	Node		Node
	3		2
	Data Ports move from
	fowarding to blocking
Control VLAN		Transit Node Links Down Message (2)
Master Node Hello Message	(1)	Ring-Down-Flush-FDB Message		(3)
				EPSR 2.eps

For a multi domain ring, this process will occur separately for each domain within the ring.