1-5secondary port receives the Hello packets sent by the local master node before the Fail timerexpires, the overall ring is in Health state. Otherwise, the ring transits into Disconnect state.z In an RRPP domain, a transit node learns the Hello timer value and the Fail timer value on themaster node through the received Hello packets, ensuring that all nodes in the ring network areconsistent in the two timer settings.z The Fail timer value must be greater than or equal to three times of the Hello timer value.z In a dual-homed-ring network, to avoid temporary loops when the primary ring fails, ensure that thedifference between the Fail timer value on the master node of the subring and that on the masternode of the primary ring is greater than twice the Hello timer value of the master node of thesubring.How RRPP WorksPolling mechanismThe polling mechanism is used by the master node of an RRPP ring to check the Health state of the ringnetwork.The master node sends Hello packets out its primary port periodically, and these Hello packets travelthrough each transit node on the ring in turn.z If the ring is complete, the secondary port of the master node will receive Hello packets before theFail timer expires and the master node will keep the secondary port blocked.z If the ring is torn down, the secondary port of the master node will fail to receive Hello packetsbefore the Fail timer expires. The master node will release the secondary port from blocking dataVLANs while sending Common-Flush-FDB packets to instruct all transit nodes to update their ownMAC entries and ARP/ND entries.Link down alarm mechanismThe transit node, the edge node or the assistant-edge node sends Link-Down packets to the masternode immediately when they find any of its own ports belonging to an RRPP domain is down. Upon thereceipt of a Link-Down packet, the master node releases the secondary port from blocking data VLANswhile sending Common-Flush-FDB packet to instruct all the transit nodes, the edge nodes and theassistant-edge nodes to update their own MAC entries and ARP/ND entries. After each node updatesits own entries, traffic is switched to the normal link.Ring recoveryThe master node may find the ring is restored after a period of time after the ports belonging to theRRPP 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 ofthe 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 theseports.
