Specifications

180 ExtremeWare XOS 11.0 Concepts Guide
Ethernet Automatic Protection Switching
When the broken link is restored, the master receives its health check packet back on its secondary port
and once again declares the ring to be complete. Again, the master node logically:
• Blocks the protected VLANs on its secondary port.
• Flushes its FDB.
• Sends 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 their
forwarding databases.
When the transit nodes receive the message to flush their forwarding databases, they perform these
steps:
1 Flush their 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.
Multiple EAPS Domains
This section illustrates how you can work with more than one EAPS domain.
EAPS Data VLAN Spanning Two Rings Connected by One Switch
Figure 13 shows how a data VLAN could span two rings interconnected by a common switch—a
“figure eight” topology. In this example, there is an EAPS domain with its own control VLAN running
on ring 1 and another EAPS domain with its own control VLAN running on ring 2. A data VLAN that
spans both rings will be added as a protected VLAN to both EAPS domains. In Figure 13, switch S5 will
have two instances of EAPS domains running on it: one for each ring.