Dell Force10 S4820T S4820T Configuration Guide - Page 387

The Master node continues sending Ring Health Frames out its primary port even when operating in the Ring-Fault state. Once the ring is restored, the next status check frame is received on the Master node's Secondary port. This will cause 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. However, it is not recommended on the S20/S50 to have more than 34 rings on the same interface (either a physical interface or a portchannel). More than the recommended number of rings may cause interface instability. Multiple rings can be configured with a single switch connection; a single ring can have multiple FRRP groups; multiple rings can be connected with a common link. The S4810, S4820T, S55, and S60 support up to 32 rings on a system (including stacked units). 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 example shown below, 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. Important FRRP Points FRRP provides a convergence time that can generally range between 150ms and 1500ms for Layer 2 networks. The master node originates a high-speed frame that circulates around the ring. This frame, appropriately, sets up or breaks down the ring. • Ring Status Check Frames are transmitted by the Master Node at specified intervals • Multiple physical rings can be run on the same switch • One Master node per ring-all other nodes are Transit Force10 Resilient Ring Protocol (FRRP) | 387