Configuring Traffic Storm Control

Information About Traffic Storm Control

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 Ethernet interfaces by a broadcast, unknown multicast, or unknown unicast traffic storm.

Traffic storm control (also called traffic suppression) allows you to monitor the levels of the incoming broadcast, unknown multicast, or unknown unicast traffic over a 10-microsecond 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.

The following figure shows the broadcast traffic patterns on an Ethernet interface during a specified time 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.

Figure 1. Broadcast Suppression

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

Traffic storm control is implemented in the hardware. The traffic storm control circuitry monitors packets that pass from an Ethernet 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-microsecond 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-microsecond interval can affect the operation of traffic storm control.

The following are examples of how traffic storm control operation is affected:

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

  • If you enable unknown multicast traffic storm control, and the learned multicast traffic exceeds the level within the 10-microsecond interval, traffic storm control drops all exceeding multicast traffic until the end of the interval.

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

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

By default, Cisco NX-OS takes no corrective action when traffic exceeds the configured level.

Guidelines and Limitations for Traffic Storm Control

When configuring the traffic storm control level, follow these guidelines and limitations:

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

  • 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.

  • There are local link and hardware limitations that prevent storm-control drops from being counted separately. Instead, storm-control drops are counted with other drops in the discards counter.

  • 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.

  • The range of learned multicast will be changed by setting igmp snooping.

  • The link-level control protocols (LACP, LLDP and so on) are not affected in case of a traffic storm. The storm control is applied to data plane traffic only.

  • The burst size values are:

    • For a 10G port, 48.68 Mbytes/390Mbits

    • For a 1G port, 25 Mbytes/200Mbits

Default Settings for Traffic Storm Control

The following table lists the default settings for traffic storm control parameters.

Table 1. Default Traffic Storm Control Parameters

Parameters

Default

Traffic storm control

Disabled

Threshold percentage

100

Configuring Traffic Storm Control

You can set the percentage of total available bandwidth that the controlled traffic can use.


Note

Traffic storm control uses a 10-microsecond interval that can affect the operation of traffic storm control.

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# interface {ethernet slot/port | port-channel number}
  3. switch(config-if)# storm-control [broadcast | multicast | unicast] level percentage[.fraction]

DETAILED STEPS

  Command or Action Purpose

Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

switch(config)# interface {ethernet slot/port | port-channel number}

Enters interface configuration mode.

Step 3

switch(config-if)# storm-control [broadcast | multicast | unicast] level percentage[.fraction]

Configures traffic storm control for traffic on the interface. The default state is disabled.Also configures an optional corrective action that can be performed when traffic exceeds the configured level:

  • shutdown —Shuts down the port or puts it in the error-disable state.

  • trap —Generates an SNMP trap.

Example

This example shows how to configure traffic storm control for port channels 122 and 123: 

switch# configure terminal
switch(config)# interface port-channel 122, port-channel 123
switch(config-if-range)# storm-control unicast level 66.75
switch(config-if-range)# storm-control multicast level 66.75
switch(config-if-range)# storm-control broadcast level 66.75
switch(config-if-range)#

Verifying the Traffic Storm Control Configuration

Use the following commands to display traffic storm control configuration information:

Command

Purpose

show interface [ethernet slot/port | port-channel number] counters storm-control

Displays the traffic storm control configuration for the interfaces.

Note

 

Traffic storm control uses a 10-microsecond interval that can affect the operation of traffic storm control.

show running-config interface

Displays the traffic storm control configuration.


Note

When a storm event occurs on a port and the packets are dropped due to storm control configuration, a syslog message is generated to indicate that the storm event has started. An additional syslog message is generated when the storm event ends and the packet are no longer dropped.

Traffic Storm Control Example Configuration

This example shows how to configure traffic storm control: 

switch# configure terminal
switch(config)# interface ethernet 1/4
switch(config-if)# storm-control action trap
switch(config-if)# storm-control broadcast level 40
switch(config-if)# storm-control multicast level 40
switch(config-if)# storm-control unicast level 40

This example shows how to specify the number of Storm Control traps per minute: 

switch# configure terminal
switch(config)# snmp-server enable traps storm-control trap-rate 100
switch(config)#