Page 6 | AlliedWare™ OS How To Note: EPSR
How EPSR Works
new configuration, the nodes (master and transit) re-learn their layer 2 addresses. During
this period, the master node continues to send Health messages over the control VLAN.
This situation continues until the faulty link or node is repaired.
For a multidomain ring, this process occurs separately for each domain within the ring.
The following figure shows the flow of control frames when a link breaks.
Fault in the master node
If the master node goes down, the transit nodes simply continue forwarding traffic around
the ring—their operation does not change.
The only observable effects on the transit nodes are that:
• They stop receiving Health messages and other messages from the master node.
• The transit nodes connected to the master node experience a broken link, so they send
Link-Down messages. If the master node is down these messages are simply dropped.
Neither of these symptoms affect how the transit nodes forward traffic.
Once the master node recovers, it continues its function as the master node.
Master
Node
Transit
Node
1
Transit
Node
4
Transit
Node
2
Control VLAN
Ring-Down-Flush-FDB Message
Transit
Node
3
Control VLAN is forwarding
Data VLANs are forwarding
Control VLAN is forwarding
Data VLANs move from blocking
to forwarding
Data ports move from
fowarding to blocking
Transit Node Link-Down Message
Master Node Health Message
P
S
epsr-broken-ring
1
2
3
1
2
3
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