Administrator Guide

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 non-
control 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.
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 pre- forwarding state. When the Transit node in the pre-forwarding state receives
the control frame instructing it to clear its routing table, it does so and unblocks the previously blocked ring
ports on the newly restored port. Then the Transit node returns to the Normal state.
Multiple FRRP Rings
Up to 255 rings are allowed per system and multiple rings can be run on one system.
More than the recommended number of rings may cause interface instability. You can configure multiple
rings with a single switch connection; a single ring can have multiple FRRP groups; multiple rings can be
connected with a common link.
Force10 Resilient Ring Protocol (FRRP) 361