H3C Technologies H3C S10500 Series Switches - Manual (Page 63)

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NOTE:
In an RRPP domain, a transit node learns the Hello timer value and the Fail timer value on the master node
through the received Hello packets, ensuring that all nodes in the ring network are consistent in the two
timer settings. A transit node, however, cannot learn the Fast-Hello timer value and the Fast-Fail timer
value set on the master node through received Fast-Hello packets.
How RRPP works
Polling mechanism
The polling mechanism is used by the master node of an RRPP ring to check the Health state of the ring
network.
The master node sends Hello packets out its primary port periodically, and these Hello packets travel
through each transit node on the ring in turn.
• If the ring is complete, the secondary port of the master node will receive Hello packets before the
Fail timer expires and the master node will keep the secondary port blocked.
• If the ring is torn down, the secondary port of the master node will fail to receive Hello packets
before the Fail timer expires. The master node will release the secondary port from blocking data
VLANs and sending Common-Flush-FDB packets to instruct all transit nodes to update their own
MAC entries and ARP/ND entries.
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 of its own ports belonging to an RRPP domain are down. Upon the
receipt of a Link-Down packet, the master node releases the secondary port from blocking data VLANs
and sending Common-Flush-FDB packet to instruct all the transit nodes, the edge nodes, and the
assistant-edge nodes to update their own MAC entries and ARP/ND entries. After each node updates its
own entries, traffic is switched to the normal link.
Ring recovery
The master node may find that the ring is restored after a period of time after the ports belonging to the
RRPP domain on the transit nodes, the edge nodes, or the assistant-edge nodes are brought up again. A
temporary loop may arise in the data VLAN during this period. As a result, broadcast storm occurs.
To prevent temporary loops, non-master nodes block them immediately (and permit only the packets of
the control VLAN to pass through) when they find their ports accessing the ring are brought up again.
The blocked ports are activated only when the nodes are sure that no loop will be brought forth by these
ports.
Broadcast storm suppression mechanism in a multi-homed subring in case of SRPT failure
As shown in
Figure
17 , Ring 1 is the primary ring, and Ring 2 and Ring 3 are subrings. When the two
SRPTs between the edge node and the assistant-edge node are down, the master nodes of Ring 2 and
Ring 3 will open their respective secondary ports, generating a loop among Device B, Device C, Device
E, and Device F. As a result, a broadcast storm occurs.
To prevent generating this loop, the edge node will block the edge port temporarily. The blocked edge
port is activated only when the edge node is sure that no loop will be brought forth when the edge port
is activated.