Cisco Nexus 6000 Series NX-OS Layer 2 Switching Configuration Guide, Release 6.x
Configuring Traffic Storm Control
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Configuring Traffic Storm Control

This chapter contains the following sections:

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, multicast, or unknown unicast traffic storm.

Traffic storm control (also called traffic suppression) allows you to monitor the levels of the incoming broadcast, 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 multicast traffic storm control, and the 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 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 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 the 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.
  • You can configure traffic storm control on a fabric port or a fabric port channel that connects the switch to a Fabric Extender (FEX). Storm control configured on a FEX applies to the aggregate traffic coming in on all the ports on that FEX.

    Note


    The NIF storm control feature applies on all traffic coming in on a FEX fabric port. Traffic that comes on the FEX fabric port with the VNTAG header has an additional 6 bytes added to the original traffic. Due to these additional 6 bytes of overhead, the rate at which the traffic is policed by the storm control policer is skewed depending on the packet size of the original traffic that is ingressing on the HIF ports. The skew is larger for the smaller packet sizes compared to the larger packet sizes.


  • 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 indiscards 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.
  • Applying storm control over a HIF range is not recommended. The configuration might fail for one or more interfaces in the range depending on the hardware resource availability. The result of the command is partial success in some cases.

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.


Procedure
      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.

    Note   

    If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

     
    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.

     

    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.

    Note   

    If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

    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

    The following example shows how to configure traffic storm control:

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

    Default Traffic Storm Settings

    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