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This chapter contains the following sections:
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 or multicast traffic storm.
Traffic storm control (also called traffic suppression) allows you to monitor the levels of the incoming broadcast or multicast 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.
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 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:
By default, Cisco NX-OS takes no corrective action when the traffic exceeds the configured level.
When configuring the traffic storm control level, follow these guidelines and limitations:
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. |
This example shows how to configure multicast traffic storm control for Ethernet interface 1/4:
switch# configure terminal switch(config)# interface ethernet 1/4 switch(config-if)# storm-control multicast level 40
To display traffic storm control configuration information, perform one of these tasks:
Command |
Purpose |
||
---|---|---|---|
switch# show interface [ethernet slot/port | port-channel number] counters storm-control | Displays the traffic storm control configuration for the interfaces.
|
||
switch# 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. |
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
The following table lists the default settings for traffic storm control parameters.
Parameters |
Default |
---|---|
Traffic storm control |
Disabled |
Threshold percentage |
100 |