Restoration Operations - Extreme Networks 200 Series Installation And User Manual

Ethernet Automatic Protection Switching
Polling
The master node (including a Summit stack operating as the master node) transmits a health-check
packet on the control VLAN at a user-configurable interval (see Figure 26). 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
the 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.
Trap Message Sent by a Transit Node
When any transit node (including a Summit stack operating as a 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 27), 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.

Restoration Operations

The master node continues sending health-check packets out its primary port even when the master
node is operating in the failed state. As long as there is a break in the ring, the fail-period timer of the
master node will continue to expire and the master node will remain in the failed state.
When the broken link is restored, the master will receive its health-check packet back on its secondary
port, and will once again declare the ring to be complete. It will logically block the protected VLANs on
its secondary port, flush its FDB, and send a "flush FDB" message to its associated transit nodes.
During the time between when the transit node detects that the link is operable again and when the
master node detects that the ring is complete, the secondary port on the master node is still open and
data could start traversing the transit node port that just came up. To prevent the possibility of a such a
temporary loop, when the transit node detects that its failed link is up again, it will perform these steps:
1 For the port that just came up, put all the protected VLANs traversing that port into a temporary
blocked state.
2 Remember which port has been temporarily blocked.
3 Set the state to Preforwarding.
When the master node receives its health-check packet back on its secondary port, and detects that the
ring is once again complete, it sends a message to all its associated transit nodes to flush the forwarding
databases.
When the transit nodes receive the message to flush the forwarding databases, they perform these steps:
1 Flush the forwarding databases on the protected VLANs.
2 If the port state is set to Preforwarding, unblock all the previously blocked protected VLANs for the
port.
146 Summit 200 Series Switch Installation and User Guide