Defining Storm Control
When Broadcast, Multicast, or Unknown Unicast frames are received, they are duplicated, and a copy is sent to all possible egress ports. This means that in practice they are sent to all ports belonging to the relevant VLAN. In this way, one ingress frame is turned into many, creating the potential for a traffic storm.
Storm protection enables you to limit the number of frames entering the device and to define the types of frames that are counted towards this limit.
When the rate of Broadcast, Multicast, or Unknown Unicast frames is higher than the user-defined threshold, frames received beyond the threshold are discarded.
To define Storm Control:
- Click Security > Storm Control.
All the fields on this page are described in the Edit Storm Control page except for the Storm Control Rate Threshold (%). It displays the percent of the total available bandwidth for unknown Unicast, Multicast, and Broadcast packets before storm control is applied at the port. The default value is 10% of the maximum rate of the port and is set in the Edit Storm Control page.
- Select a port and click Edit.
- Enter the parameters.
- Interface—Select the port for which storm control is enabled.
- Storm Control—Select to enable Storm Control.
- Storm Control Rate Threshold—Enter the maximum rate at which unknown packets can be forwarded. The default for this threshold is 10,000 for FE devices and 100,000 for GE devices.
- Storm Control Mode—Select one of the modes:
- Unknown Unicast, Multicast & Broadcast—Counts unknown Unicast, Broadcast, and Multicast traffic towards the bandwidth threshold.
- Multicast & Broadcast—Counts Broadcast and Multicast traffic towards the bandwidth threshold.
- Broadcast Only—Counts only Broadcast traffic towards the bandwidth threshold.
- Click Apply. Storm control is modified, and the Running Configuration file is updated.