H3C Technologies H3C S12500 Series Switches - Manual (Page 70)

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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 of 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 is 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 might find 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 might 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 from
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 generated by these
ports.
Broadcast storm suppression mechanism in case of SRPT failure in a multi-homed subring
As shown in Figure 15 , 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 and causing a broadcast storm.
To prevent generating a loop, the edge node will temporarily block the edge port. The blocked edge port
is activated only when the edge node is sure that no loop will be generated when the edge port is
activated.
Load balancing
In a ring network, traffic from multiple VLANs might be transmitted at the same time. RRPP can implement
load balancing for the traffic by transmitting traffic from different VLANs along different paths.
By configuring an individual RRPP domain for transmitting the traffic from the specified VLANs (protected
VLANs) in a ring network, traffic from different VLANs can be transmitted according to different
topologies in the ring network for load balancing.