A traffic storm occurs when packets flood the LAN, creating excessive traffic and degrading network performance. You can use the traffic storm control feature to prevent disruptions on Layer 2 ports by a broadcast, multicast, or unicast traffic storm on physical interfaces.

Traffic storm control (also called traffic suppression) allows you to monitor the levels of the incoming broadcast, multicast, and unicast traffic over a 10-millisecond interval. During this interval, the traffic level, which is a percentage of the total available bandwidth of the port, is compared with the traffic storm control level that you configured. When the ingress traffic reaches the traffic storm control level that is configured on the port, traffic storm control drops the traffic until the interval ends.

This table shows the broadcast traffic patterns on a Layer 2 interface over a given interval. In this example, traffic storm control occurs between times T1 and T2 and between T4 and T5. During those intervals, the amount of broadcast traffic exceeded the configured threshold.

The traffic storm control threshold numbers and the time interval allow the traffic storm control algorithm to work with different levels of granularity. A higher threshold allows more packets to pass through.

Traffic storm control on the Cisco NX-OS device is implemented in the hardware. The traffic storm control circuitry monitors packets that pass from a Layer 2 interface to the switching bus. Using the Individual/Group bit in the packet destination address, the circuitry determines if the packet is unicast or broadcast, tracks the current count of packets within the 10-millisecond interval, and filters out subsequent packets when a threshold is reached.

Traffic storm control uses a bandwidth-based method to measure traffic. You set the percentage of total available bandwidth that the controlled traffic can use. Because packets do not arrive at uniform intervals, the 10-millisecond interval can affect the behavior of traffic storm control.

The following are examples of traffic storm control behavior:

• If you enable broadcast traffic storm control, and broadcast traffic exceeds the level within the 10-millisecond interval, traffic storm control drops all broadcast traffic until the end of the interval.

• If you enable broadcast and multicast traffic storm control, and the combined broadcast and multicast traffic exceeds the level within the 10-millisecond interval, traffic storm control drops all broadcast and multicast traffic until the end of the interval.

• If you enable broadcast and multicast traffic storm control, and broadcast traffic exceeds the level within the 10-millisecond interval, traffic storm control drops all broadcast and multicast traffic until the end of the interval.

• If you enable broadcast and multicast traffic storm control, and multicast traffic exceeds the level within the 10-millisecond interval, traffic storm control drops all broadcast and multicast traffic until the end of the interval.

By default, the Cisco NX-OS software takes no corrective action when the traffic exceeds the configured level. However, you can configure an Embedded Event Management (EEM) action to error-disable an interface if the traffic does not subside (drop below the threshold) within a certain time period. For information on configuring EEM, see the Cisco Nexus 7000 Series NX-OS System Management Command Reference.

Traffic storm control configuration and operation are local to the virtual device context (VDC).

For more information on VDCs, see the Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide.

The following table shows the licensing requirements for this feature:

When configuring the traffic storm control level, note the following guidelines and limitations:

• Only one suppression level is shared by all three suppression modes i.e., unicast, multicast, and broadcast. For example, if you set the broadcast level to 30 and then set the multicast level to 40, both levels are enabled and set to 40.

• You can configure traffic storm control on a port-channel interface.

• Do not configure traffic storm control on interfaces that are members of a port-channel interface. Configuring traffic storm control on interfaces that are configured as members of a port channel puts the ports into a suspended state.

• When you use the storm-control unicast level percentage command in a module, both the unknown and known unicast traffic gets discarded after reaching the threshold value.

• Traffic storm control on all Cisco FEX devices connected to Cisco Nexus 7000 series switches has following guidelines and limitations:

  • Traffic storm control is not supported on HIF ports.

  • Traffic storm control is supported only on NIF ports.

• Specify the level as a percentage of the total interface bandwidth:

  • The level can be from 0 to 100.

  • The optional fraction of a level can be from 0 to 99.

  • 100 percent means no traffic storm control.

  • 0.0 percent suppresses all traffic.

Because of hardware limitations and the method by which packets of different sizes are counted, the level percentage is an approximation. Depending on the sizes of the frames that make up the incoming traffic, the actual enforced level might differ from the configured level by several percentage points.

Note	If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.

This table lists the default settings for traffic storm control parameters.

To display traffic storm control configuration information, perform one of the following tasks:

For detailed information about the fields in the output from these commands, see the Cisco Nexus 7000 Series NX-OS Security Command Reference.

The following example shows how to configure traffic storm control:

interface Ethernet1/1 
  storm-control broadcast level 40 
  storm-control multicast level 40 
  storm-control unicast level 40

This table lists the release history for this feature.