During the time between the Transit node detecting that its link is restored and the Master node detectingthat the ring is restored, the Master node’s Secondary port is still forwarding traffic. This can create atemporary loop in the topology. To prevent this, the Transit node places all the ring ports transiting the newlyrestored port into a temporary blocked state. The Transit node remembers which port has been temporarilyblocked and places it into a pre- forwarding state. When the Transit node in the pre-forwarding state receivesthe control frame instructing it to clear its routing table, it does so and unblocks the previously blocked ringports on the newly restored port. Then the Transit node returns to the Normal state.Multiple FRRP RingsUp 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 multiplerings with a single switch connection; a single ring can have multiple FRRP groups; multiple rings can beconnected with a common link.Member VLAN Spanning Two Rings Connected by OneSwitchA 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 aTransit node for both rings.In the following example, FRRP 101 is a ring with its own Control VLAN, and FRRP 202 has its own ControlVLAN running on another ring. A Member VLAN that spans both rings is added as a Member VLAN to bothFRRP groups. Switch R3 has two instances of FRRP running on it: one for each ring. The example topologythat follows shows R3 assuming the role of a Transit node for both FRRP 101 and FRRP 202.Important FRRP PointsFRRP provides a convergence time that can generally range between 150ms and 1500ms for Layer 2networks.The Master node originates a high-speed frame that circulates around the ring. This frame, appropriately, setsup or breaks down the ring.• The Master node transmits ring status check frames at specified intervals.• You can run multiple physical rings on the same switch.• One Master node per ring — all other nodes are Transit.• Each node has two member interfaces — primary and secondary.• There is no limit to the number of nodes on a ring.• Master node ring port states — blocking, pre-forwarding, forwarding, and disabled.• Transit node ring port states — blocking, pre-forwarding, forwarding, and disabled.• STP disabled on ring interfaces.• Master node secondary port is in blocking state during Normal operation.• Ring health frames (RHF)• Hello RHF: sent at 500ms (hello interval); Only the Master node transmits and processes these.Force10 Resilient Ring Protocol (FRRP) 454
