15Force10 Resilient Ring Protocol (FRRP)FRRP provides fast network convergence to Layer 2 switches interconnected in a ring topology, such as ametropolitan area network (MAN) or large campuses. FRRP is similar to what can be achieved with thespanning tree protocol (STP), though even with optimizations, STP can take up to 50 seconds toconverge (depending on the size of network and node of failure) may require 4 to 5 seconds toreconverge. FRRP can converge within 150ms to 1500ms when a link in the ring breaks (depending onnetwork configuration).To operate a deterministic network, a network administrator must run a protocol that convergesindependently of the network size or node of failure. FRRP is a proprietary protocol that provides thisflexibility, while preventing Layer 2 loops. FRRP provides sub-second ring-failure detection andconvergence/re-convergence in a Layer 2 network while eliminating the need for running spanning-treeprotocol. With its two-way path to destination configuration, FRRP provides protection against any singlelink/switch failure and thus provides for greater network uptime.Protocol OverviewFRRP is built on a ring topology.You can configure up to 255 rings on a system. FRRP uses one Master node and multiple Transit nodes ineach ring. There is no limit to the number of nodes on a ring. The Master node is responsible for theintelligence of the Ring and monitors the status of the Ring. The Master node checks the status of theRing by sending ring health frames (RHF) around the Ring from its Primary port and returning on itsSecondary port. If the Master node misses three consecutive RHFs, the Master node determines the ringto be in a failed state. The Master then sends a Topology Change RHF to the Transit Nodes informingthem that the ring has changed. This causes the Transit Nodes to flush their forwarding tables, and re-converge to the new network structure.One port of the Master node is designated the Primary port (P) to the ring; another port is designated asthe Secondary port (S) to the ring. In normal operation, the Master node blocks the Secondary port for allnon-control traffic belonging to this FRRP group, thereby avoiding a loop in the ring, like STP. Layer 2switching and learning mechanisms operate per existing standards on this ring.Each Transit node is also configured with a Primary port and a Secondary port on the ring, but the portdistinction is ignored as long as the node is configured as a Transit node. If the ring is complete, theMaster node logically blocks all data traffic in the transmit and receive directions on the Secondary portto prevent a loop. If the Master node detects a break in the ring, it unblocks its Secondary port and allowsdata traffic to be transmitted and received through it. Refer to the following illustration for a simpleexample of this FRRP topology. Note that ring direction is determined by the Master node’s Primary andSecondary ports.A virtual LAN (VLAN) is configured on all node ports in the ring. All ring ports must be members of theMember VLAN and the Control VLAN.278 Force10 Resilient Ring Protocol (FRRP)
