Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 453

Each Transit node is also configured with a Primary port and a Secondary port on the ring, but the port distinction is ignored as long as the node is configured as a Transit node. If the ring is complete, the Master node logically blocks all data traffic in the transmit and receive directions on the Secondary port to prevent a loop. If the Master node detects a break in the ring, it unblocks its Secondary port and allows data traffic to be transmitted and received through it. Refer to the following illustration for a simple example of this FRRP topology. 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 the Member 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 pass through all ports in the ring, including the secondary port of the Master node. Ring Status The ring failure notification and the ring status checks provide two ways to ensure the ring remains up and active in the event of a switch or port failure. Ring Checking At specified intervals, the Master node sends a ring health frame (RHF) through the ring. If the ring is complete, the frame is received on its secondary port and the Master node resets its fail-period timer and continues normal operation. If the Master node does not receive the RHF before the fail-period timer expires (a configurable timer), the Master node moves from the Normal state to the Ring-Fault state and unblocks its Secondary port. The Master node also clears its forwarding table and sends a control frame to all other nodes, instructing them to also clear their forwarding tables. Immediately after clearing its forwarding table, each node starts learning the new topology. Ring Failure If a Transit node detects a link down on any of its ports on the FRRP ring, it immediately sends a link-down control 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 the Ring-Fault state and unblocks its Secondary port. The Master node clears its routing table and sends a control frame to all other ring nodes, instructing them to clear their routing tables as well. Immediately after clearing its routing table, each node begins learning the new topology. Ring Restoration The Master node continues sending ring health frames out its primary port even when operating in the RingFault state. After the ring is restored, the next status check frame is received on the Master node's Secondary port. This causes the Master node to transition back to the Normal state. The Master node then logically blocks noncontrol frames on the Secondary port, clears its own forwarding table, and sends a control frame to the Transit nodes, instructing them to clear their forwarding tables and re-learn the topology. Force10 Resilient Ring Protocol (FRRP) 453