6
Software Reference
Restoring Normal Operation
Transit Nodes
Once a fault in the ring or node has been rectified, the transit nodes that span
the (previously) faulty link section will detect that link connectivity has
returned. They will then move their appropriate ring port state, from
“Links-Down” to “Pre-Forwarding,” and await the “Ring-Up-Flush” control
message from the master node. See
“Master Node” on page 1-6
.
Once these transit nodes receive the “Ring-Up-Flush” message, they:
■
flush their forward databases for both their ring ports
■
change the state of their ports from blocking to forwarding, which allows
data to flow through their previously blocked ring ports
Note that the transit nodes do not enter the forward state until they have
received the “Ring-Up-Flush” message. This is to prevent the possibility of a
loop condition occurring caused by the transit nodes moving into the
forwarding state before the master node secondary port is able to return to the
blocking state. During such a period, the ring would have no ports blocked.
Master Node
With the link restored, the healthcheck messages that are sent from the primary
port of the master node now complete the loop and arrive at the master node’s
secondary port. The master node now takes the following steps to restore
normal conditions:
■
declares the ring to be in a “complete” state
■
blocks its secondary port for data (non-control) traffic
■
flushes its forwarding database for its two ring ports
■
sends a “Ring-Up-Flush-FDB” message from its primary port, to all transit
nodes.
