3Com 7757 Configuration Manual page 907

Typical Networking of
RRPP
To avoid temporary data loops, when detecting the port through which it connects
to the ring network becomes UP again, a transit node blocks the port temporarily
(only control VLAN packets are permitted to pass), and keeps the port blocked
until it receives the Complete Flush packet from the master node.
The following details how to unblock the temporarily blocked port:
When the master node is in the Fail status, if the secondary port receives the
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HEALTH sent by the primary port, the master node believes that the ring
network has been recovered. Thus, the node status is transited to the
Complete status and the master node sends the Complete Flush message
through the primary port to request the transit node to update the FDB and
unblock the temporarily blocked port. After the transit node receives the
Complete Flush message, it unblocks the temporarily blocked port.
If the transit node does not receive the Complete Flush message after the Fail
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timer expires, it automatically unblocks the temporarily blocked port.
To ensure normal RRPP operation, you must configure RRPP correctly. Here are
several typical networking applications.
Single ring network
Figure 251 Single ring network
Switch A
Master node
Transit node
Switch D
There is only one ring in the network topology. In this case, only one RRPP domain
is to be defined.
Domain 1
Switch B
Transit node
Ring 1
Transit node
Switch C
RRPP Overview 907