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.

Control VLAN is forwarding

 

 

Control VLAN is forwarding

Data VLANs move from blocking

 

 

Data VLANs are forwarding

to forwarding

 

 

 

 

 

S

P

3

 

 

 

 

 

 

 

2

 

 

 

 

1

 

 

 

Master

 

 

Transit

 

Node

Transit

 

 

 

 

Node

 

 

Node

 

4

 

 

1

 

Transit

 

 

Transit

 

Node

 

 

Node

 

3

 

 

2

 

 

Data ports move from

 

 

 

fowarding to blocking

 

 

 

Master Node Health Message

1

Control VLAN

Transit Node Link-Down Message

2

 

Ring-Down-Flush-FDB Message

3

 

 

 

 

epsr-broken-ring

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.

Page 6 AlliedWare™ OS How To Note: EPSR

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Allied Telesis AT-9924T/4SP-A-20, X900-48FE-N, AT-8948, AT-9924T-40, AT-9924SP-30 manual Fault in the master node

AT-9924SP-30, AT-9924T-40, AT-8948, AT-9924T/4SP-A-20, X900-48FE-N specifications

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