3Com Switch 4800G 24-Port Configuration Manual page 1141

As shown in Figure 343, Ring 1 is the primary ring and Ring 2 is a sub ring. Device
A is the master node of Ring 1, Device B, Device C and Device D are the transit
nodes of Ring 1; Device E is the master node of Ring 2, Device B is the edge node
of Ring 2, and Device C is the assistant edge node of Ring 2.
Primary port and secondary port
Each master node or transit node has two ports accessing an RRPP ring, in which
one serves as the primary port and the other serves as the secondary port. You can
determine the role of a port.
1 In terms of functionality, the difference between the primary port and the
secondary port of a master node is:
The primary port and the secondary port are designed to play the role of
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sending and receiving loop-detect packets respectively.
When an RRPP ring is in health state, the secondary port of the master node
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will logically deny data VLANs and permit only the packets of the control
VLANs.
When an RRPP ring is in disconnect state, the secondary port of the master
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node will permit data VLANs, that is, forward packets of data VLANs.
2 In terms of functionality, there is no difference between the primary port and the
secondary port of the transit node. Both are designed for the transfer of protocol
packets and data packets over an RRPP ring.
As shown in Figure 343, Device A is the master node of Ring 1. Port 1 and port 2
are the primary port and the secondary port of the master node on Ring 1
respectively. Device B, Device C and Device D are the transit nodes of Ring 1. Their
port 1 and port 2 are the primary port and the secondary port on Ring 1
respectively.
Common port and edge port
Each edge node or assistant edge node have two ports accessing a sub ring, with
one being a common port and the other being an edge port. Common port is a
port accessing the primary ring and a sub ring simultaneously; and edge port is a
port accessing only a sub ring.
As shown in Figure 343, Device B and Device C lie on Ring 1 and Ring 1. Device B's
port 2 and Device C's port 1 access the primary ring and a sub ring at the same
time, so they are common ports. Device B's port 3 and Device C's port 3 access
only a sub ring, so they are edge ports.
Multi-domain intersection common port
Of the two ports on a node where rings of different domains intersect, the
common port is the one on the primary ring that belongs to different domains at
the same time. This port must not be on a sub ring. The role of the port is
determined by user configuration.
Timers
The master node uses two timers to send and receive RRPP packets: the Hello
timer and the Fail timer.
The Hello timer is used for the primary port to send Health packets.
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RRPP Overview 1141