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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.
Member VLAN Spanning Two Rings Connected by One Switch
A member VLAN can span two rings interconnected by a common switch, in a figure-eight style
topology.
A switch can act as a Master node for one FRRP group and a Transit for another FRRP group, or it can be
a Transit node for both rings.
In the following example, FRRP 101 is a ring with its own Control VLAN, and FRRP 202 has its own Control
VLAN running on another ring. A Member VLAN that spans both rings is added as a Member VLAN to both
FRRP groups. Switch R3 has two instances of FRRP running on it: one for each ring. The example
topology that follows shows R3 assuming the role of a Transit node for both FRRP 101 and FRRP 202.
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Force10 Resilient Ring Protocol (FRRP)