Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 1487)

EPSR Introduction and Configuration
Software Reference for x310 Series Switches
C613-50046-01 REV A AlliedWare Plus TM Operating System - Version 5.4.4C 57.5
Figure 57-2: EPSR Fault Detection Messages
Restoring Normal Operation
Transit nodes Once a fault in the ring or node has been rectified, the transit nodes that span the
previously faulty link section detect that link connectivity has returned. They then move
their appropriate ring port state, from Links-Down to Pre-Forwarding, and await the Ring-
Up-Flush control message from the master node.
Once these transit nodes receive the Ring-Up-Flush message, they:
■ flush their forward databases for both their ring ports.
■ change the state of their ports from blocking to forwarding, which allows data to flow
through their previously blocked ring ports.
Master node With the link restored, the healthcheck messages that are sent from the primary port of
the master node now complete the loop and arrive at the master node’s secondary port.
The master node restores normal conditions as follows:
1. Declares the ring to be in a “complete” state.
2. Blocks its secondary port for data (non-control) traffic.
3. Flushes its forwarding database for its two ring ports.
4. Sends a Ring-Up-Flush-FDB message from its primary port, to all transit nodes.
Master
Node
Transit
Node
1
Transit
Node
4
Transit
Node
2
Master Node Hello Message
Control VLAN
Ring-Down-Flush-FDB Message
Transit
Node
3
EPSR 2.eps
Control Vlan “forwarding”
Data VLANs “forwarding”
Control VLAN “forwarding”
Data VLANs
“move from blocking to forwarding”
Data Ports move from
fowarding to blocking
Transit Node Links Down Message
P S
(1)
(2)
(3)
Note The transit nodes do not enter the forward state until they have received the
Ring-Up-Flush message. This prevents the possibility of a loop condition
occurring caused by the transit nodes moving into the forwarding state before
the master node secondary port can return to the blocking state. During such a
period, the ring would have no ports blocked.