Configuring Storm Control

A broadcast storm occurs when a switch port receives a large number of broadcast packets, and forwarding these packets causes the network to slow down or time out. Unicast and multicast storms are similar, except that the port receives unicast or multicast packets as a result of the storm. The broadcast rate and forwarding rate are maintained on a per-port basis, not on a per-VLAN basis.

On Catalyst 2900 XL, 2950, and 3500 XL switches, two thresholds define the beginning and the end of a storm. The rising threshold is the number of broadcast, unicast, or multicast packets per second that a switch port can receive before forwarding is blocked. The falling threshold re-enables the normal forwarding of broadcast, unicast, or multicast packets. You can set a filter that either controls traffic or shuts down the port during a storm and sends a trap to notify the SNMP manager when a threshold is crossed.

On Catalyst 3550 switches, you can set a suppression levela percentage of interface bandwidthfor broadcast, unicast, and multicast traffic. If the percentage is exceeded, no traffic of the specified type is fowarded by the interface.

Note: You cannot configure storm control on Catalyst 1900 and 2820 switches.

To configure storm control, choose Port > Flooding Control and use the Flooding Control window.