Concept Guide

Force10 Resilient Ring Protocol (FRRP)
FRRP provides fast network convergence to Layer 2 switches interconnected in a ring topology, such as a metropolitan area network
(MAN) or large campuses.
FRRP is similar to what can be achieved with the spanning tree protocol (STP), though even with optimizations, STP can take up to 50
seconds to converge (depending on the size of network and node of failure) may require 4 to 5 seconds to reconverge. FRRP can converge
within 150ms to 1500ms when a link in the ring breaks (depending on network conguration).
To operate a deterministic network, a network administrator must run a protocol that converges independently of the network size or node
of failure. FRRP is a proprietary protocol that provides this exibility, while preventing Layer 2 loops. FRRP provides sub-second ring-failure
detection and convergence/re-convergence in a Layer 2 network while eliminating the need for running spanning-tree protocol. With its
two-way path to destination conguration, FRRP provides protection against any single link/switch failure and thus provides for greater
network uptime.
Topics:
• Protocol Overview
• Implementing FRRP
• FRRP Conguration
• Troubleshooting FRRP
• Sample Conguration and Topology
• FRRP Support on VLT
Protocol Overview
FRRP is built on a ring topology.
You can congure up to 255 rings on a system. FRRP uses one Master node and multiple Transit nodes in each ring. There is no limit to the
number of nodes on a ring. The Master node is responsible for the intelligence of the Ring and monitors the status of the Ring. The Master
node checks the status of the Ring by sending ring health frames (RHF) around the Ring from its Primary port and returning on its
Secondary port. If the Master node misses three consecutive RHFs, the Master node determines the ring to be in a failed state. The
Master then sends a Topology Change RHF to the Transit Nodes informing them that the ring has changed. This causes the Transit Nodes
to ush 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 as the Secondary port (S) to the
ring. In normal operation, the Master node blocks the Secondary port for all non-control trac belonging to this FRRP group, thereby
avoiding a loop in the ring, like STP. Layer 2 switching and learning mechanisms operate per existing standards on this ring.
Each Transit node is also congured with a Primary port and a Secondary port on the ring, but the port distinction is ignored as long as the
node is congured as a Transit node. If the ring is complete, the Master node logically blocks all data trac in the transmit and receive
directions on the Secondary port to prevent a loop. If the Master node detects a break in the ring, it unblocks its Secondary port and allows
data trac to be transmitted and received through it. Refer to the following illustration for a simple example of this FRRP topology. Note
that ring direction is determined by the Master node’s Primary and Secondary ports.
20
Force10 Resilient Ring Protocol (FRRP) 319