Each Transit node is also configured with a Primary port and a Secondary port on the ring, but the portdistinction is ignored as long as the node is configured as a Transit node. If the ring is complete, the Masternode logically blocks all data traffic in the transmit and receive directions on the Secondary port to prevent aloop. If the Master node detects a break in the ring, it unblocks its Secondary port and allows data traffic to betransmitted and received through it. Refer to the following illustration for a simple example of this FRRPtopology. Note that ring direction is determined by the Master node’s Primary and Secondary ports.A virtual LAN (VLAN) is configured on all node ports in the ring. All ring ports must be members of theMember VLAN and the Control VLAN.The Member VLAN is the VLAN used to transmit data as described earlier.The Control VLAN is used to perform the health checks on the ring. The Control VLAN can always passthrough all ports in the ring, including the secondary port of the Master node.Ring StatusThe ring failure notification and the ring status checks provide two ways to ensure the ring remains up andactive in the event of a switch or port failure.Ring CheckingAt specified intervals, the Master node sends a ring health frame (RHF) through the ring. If the ring iscomplete, the frame is received on its secondary port and the Master node resets its fail-period timer andcontinues normal operation.If the Master node does not receive the RHF before the fail-period timer expires (a configurable timer), theMaster node moves from the Normal state to the Ring-Fault state and unblocks its Secondary port. TheMaster node also clears its forwarding table and sends a control frame to all other nodes, instructing them toalso clear their forwarding tables. Immediately after clearing its forwarding table, each node starts learning thenew topology.Ring FailureIf a Transit node detects a link down on any of its ports on the FRRP ring, it immediately sends a link-downcontrol frame on the Control VLAN to the Master node.When the Master node receives this control frame, the Master node moves from the Normal state to theRing-Fault state and unblocks its Secondary port. The Master node clears its routing table and sends a controlframe to all other ring nodes, instructing them to clear their routing tables as well. Immediately after clearingits routing table, each node begins learning the new topology.Ring RestorationThe Master node continues sending ring health frames out its primary port even when operating in the Ring-Fault state.After the ring is restored, the next status check frame is received on the Master node's Secondary port. Thiscauses the Master node to transition back to the Normal state. The Master node then logically blocks non-control frames on the Secondary port, clears its own forwarding table, and sends a control frame to theTransit nodes, instructing them to clear their forwarding tables and re-learn the topology.Force10 Resilient Ring Protocol (FRRP) 453
