Broadcast suppression prevents the disruption of switched ports on a LAN when a broadcast storm occurs on one of the ports. A LAN broadcast storm occurs when broadcast or multicast packets flood the LAN. A broadcast storm creates excessive traffic and degrades network performance. Errors in the implementation of the protocol stack or incorrect network configuration can cause a broadcast storm.
Sometimes a broadcast storm is seen during the attempt to ping a device that does not exist.
Storm control, or traffic suppression, monitors packets passing from an interface to the switching bus and determines if the packet is unicast, multicast, or broadcast. The switch counts the number of packets of a specified type received within the one second time interval and compares the measurement with a pre-defined suppression-level threshold.
Note: Cisco IOS Software Release 12.1(12c)E1 and later support traffic storm control and prior Cisco IOS software releases support Broadcast suppression.
By default, unicast, broadcast, and multicast storm control are disabled on the switch interfaces. The suppression level is 100 percent. You can configure storm control on a port and enter the threshold level that you want to be used by a particular type of traffic.
But, because of hardware limitations and the way in which packets of different sizes are counted, threshold percentages are approximations. Dependent upon the sizes of the packets that make up the incoming traffic, the actual enforced threshold might differ from the configured level by several percentage points.
A limitation of storm control is supported only on physical interfaces. It is not supported on EtherChannel port-channels or physical interfaces that are members of port channels, even though the command is available in the Command Line Interface (CLI).
Refer to these documents for information on how to configure broadcast suppression or traffic storm control: