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Summit24e3 Switch Installation and User Guide

Figure 23: EAPS fault detection and protection switching

A master node detects a ring fault in either of two ways:

Polling response

Trap message sent by a transit node

The master node transmits a health-check packet on the control VLAN at a user-configurable interval 
(see Figure 22). If the ring is complete, the master node will receive the health-check packet on its 
secondary port (the control VLAN is not blocked on the secondary port). When the master node 
receives the health-check packet, it resets its fail-period timer and continues normal operation.

If the master node does not receive the health-check packet before the fail-period timer expires, it 
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 forwarding 
database (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 end 
stations on the reconfigured ring topology.

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 23), it immediately declares a 
“failed” state and performs the same steps described above; it unblocks its secondary port for access by 
the protected VLANs, flushes its FDB, and sends a “flush FDB” message to its associated transit nodes.

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