Ethernet Automatic Protection Switching
ExtremeWare XOS 11.3 Concepts Guide
398
A master node detects a ring fault in one of three ways:
● Link down message sent by a transit node
● Ring port down event sent by hardware layers
● Polling response
The rest of this section describes the fault detection methods and the applicable restoration options.
Link Down Message Sent by a Transit Node
When any transit node detects a loss of link connectivity on any of its ring ports, it immediately sends a
“link down” message on the control VLAN using its good link to the master node.
When the master node receives the “link down” message (see Figure 19), it immediately declares a
“failed” state and opens its logically blocked secondary port on all the protected VLANs. Now, traffic
can flow through the master’s secondary port. The master node also flushes its FDB and sends a
message on the control VLAN to all of its associated transit nodes to flush their forwarding databases as
well, so that all of the switches can learn the new paths to Layer 2 endstations on the reconfigured ring
topology.
Figure 19: EAPS fault detection and protection switching
Ring Port Down Event Sent by Hardware Layer
When a ring port goes down on a master node switch, it is notified by the lower hardware layer and
immediately goes into a “failed” state.
If the ring port that goes down on the master node is the primary port, the secondary port is opened.
The normal operation of flushing the master node’s FDB and sending a “flush FDB” message to all
transit nodes is performed.
EW_072
S3 sends "link down"
message to
master node
Master
node
Break
in ring
Master node opens secondary port
to allow traffic to pass
S4 sends "link down"
message to master node
S 4
S 5
S 6
S 3
S 2
S 1
PS
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