Flooding Control

With the Flooding Control window, you can:

Configuring Storm Control

The Flooding Control window contains tabs for configuring three types of storm control: broadcast, unicast, and multicast 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.

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 reenables 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.

By default, broadcast storm control is disabled. To enable it:

Select the Broadcast Storm tab on the Flooding Control window.
Select one or more ports on which to configure broadcast storm control.
To select multiple ports, hold down the Ctrl key and click on individual ports; or hold down the Shift key and select the first and last port in a range.
Click Modify to display the Flooding Controls Configuration dialog box.
Enter the new settings in the dialog box.
See Storm Control Settings for information on each parameter.
Click OK to put your changes in effect and close the Flooding Controls Configuration dialog box.
Your new settings are displayed on the Broadcast Storm tab.
Click OK to close the Flooding Controls Configuration window.

Configuring Unicast Storm Control

By default, unicast storm control is disabled. To enable it:

Select the Unicast Storm tab on the Flooding Control window.
Select one or more ports on which to configure unicast storm control.
To select multiple ports, hold down the Ctrl key and click on individual ports; or hold down the Shift key and select the first and last port in a range.
Click Modify to display the Flooding Controls Configuration dialog box.
Enter the new settings in the dialog box.
See Storm Control Settings for information on each parameter.
Click OK to put your changes in effect and close the Flooding Controls Configuration dialog box.
Your new settings are displayed on the Unicast Storm tab.
Click OK to close the Flooding Controls Configuration window.

Configuring Multicast Storm Control

By default, multicast storm control is disabled. To enable it:

Select the Multicast Storm tab on the Flooding Control window.
Select one or more ports on which to configure multicast storm control.
To select multiple ports, hold down the Ctrl key and click on individual ports; or hold down the Shift key and select the first and last port in a range.
Click Modify to display the Flooding Controls Configuration dialog box.
Enter the new settings in the dialog box.
See Storm Control Settings for information on each parameter.
Click OK to put your changes in effect and close the Flooding Controls Configuration dialog box.
Your new settings are displayed on the Multicast Storm tab.
Click OK to close the Flooding Controls window.

Storm Control Settings

Interface (read-only)	Identifies the port: Fast Ethernet, Gigabit Ethernet, or ATM, the module or slot number (0, 1, or 2), and port number.
Action State	Specifies whether an action is taken during a storm, and if so, what action is to be taken. is enabled or disabled. Set this parameter to Filter to filter traffic during a storm; set it to Shutdown to shut the port down during a storm; or set it to Disable so no action is taken during a storm.
Action Status (read-only)	The current state of filtering on the port. Filter status can be active forwarding, active blocking, active shutdown, or inactive.
Trap State	Specifies whether a trap is enabled or disabled. Set this parameter to Enable to notify the SNMP trap manager when a threshold is crossed. Note: Be sure to configure a trap manager (System > SNMP Management).
Trap Status (read-only)	The current state of a trap on the port.
Rising Threshold	Enter a number from 0 to 4294967295 (broadcast packets per second). The default is 500 packets per second. Make sure you set the rising threshold larger than the falling threshold.
Falling Threshold	Enter a number from 0 to the Rising Threshold setting to determine when to deactivate broadcast storm control on the port (the unit of measure is broadcast packets per second).
Packets (read-only)	Reports the number of broadcast packets per second arriving at the port.
Traps Sent (read-only)	Reports the number of traps that have been sent.

Disabling Flooded Unicast and Multicast Traffic on a Port

By default, the switch floods packets having unknown destination MAC addresses to all ports in the VLAN. Flooded traffic does not cross VLAN boundaries, except for multi-VLAN ports, which flood traffic to all VLANs to which they are connected.

Some configurations do not require flooding. For example, a port with only manually assigned addresses has no unknown destinations, so flooding serves no purpose. Therefore, you can disable the flooding of unicast and multicast packets on a per-port basis.

To disable flooded traffic of unicast and multicast packets:

Select the Unknown MACs tab on the Flooding Control window.
Select one or more ports on which to disable unicast and multicast packet flooding.
To select multiple ports, hold down the Ctrl key and click on individual ports; or hold down the Shift key and select the first and last port in a range.
Click Modify to display the modification dialog box.
Select Disable on the Unicast and Multicast drop-down lists (or select either individually) to disable flooding of packets with unknown MAC addresses.
Click OK to put your changes in effect and close the dialog box.
Click OK to close the Flooding Controls window.