3Com Switch 4800G 24-Port Configuration Manual page 1145

Multi-domain intersecting rings
Figure 348 Multi-domain intersecting rings
There are two or more domains in a network, and there two different common
nodes between any two domains. Figure 348 defines three RRPP domains, each
containing one and only one RRPP primary ring. In the case of multi-domain
intersection, the rings in different domains are independently configured. Each
single domain can contain multiple rings, among which there must be one and
only one primary ring. The data VLAN in one domain must be isolated from the
data VLAN in another.
How RRPP Works Polling mechanism
The primary port of the master node sends Health packets across the control VLAN
periodically.
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Link down alarm mechanism
The transit node, the edge node or the assistant edge node sends Link-Down
packets to the master node immediately when they find any port belonging to an
RRPP domain is down. Upon the receipt of a Link-Down packet, the master node
releases the secondary port from blocking data VLAN while sending
Common-Flush-FDB packet to notify all the transit nodes, the edge nodes and the
assistant nodes to update their own MAC entries and ARP entries.
Ring recovery
The master node may find the ring is restored after a period of time after the ports
belonging to the RRPP domain on the transit node, the edge node or the assistant
Domain 1
Transit node
Device A
Master node
Ring 1
Transit node
Device D
Transit node
If the ring works properly, the secondary port of the master node will receive
Health packets and the master node will maintain it in block state.
If the ring is torn down, the secondary port of the master node will not receive
Health packets after the timeout timer expires. The master node will release the
secondary port from blocking data VLAN while sending Common-Flush-FDB
packets to notify all transit nodes to update their own MAC entries and ARP
entries.
RRPP Overview
Domain 2
Device B
Ring 2
Ring 3
Device C
Domain 3
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Master node
Device E
Device F
Master node