Users Guide

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 that 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 Ring-
Fault 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 relearn the topology.
During the time between the Transit node detecting that its link is restored and the Master node detecting
that the ring is restored, the Master node’s Secondary port is still forwarding traffic. This can create a
temporary loop in the topology. To prevent this, the Transit node places all the ring ports transiting the newly
restored port into a temporary blocked state. The Transit node remembers which port has been temporarily
blocked and places it into a preforwarding state. When the Transit node in the preforwarding state receives
Force10 Resilient Ring Protocol (FRRP) 424