The article explains few of the possible reasons why below log message can be observed even when the bandwidth limit is not exceeded and solution to overcome this.

Jul 31 22:16:37 labdevice l2ald[2032]: L2ALD_ST_CTL_IN_EFFECT: ae1.0: storm control in effect on the port

Storm control in affect logs seen even when the bandwidth limit is not crossed.

Aug  3 06:07:28 labdevice l2ald[2032]: L2ALD_ST_CTL_IN_EFFECT: xxxxx: storm control in effect on the port

Storm control enables the switch to monitor traffic levels and to drop broadcast, multicast, and unknown unicast (BUM) packets when a specified traffic level—called the storm control level—is exceeded and a log message similar to above seen, will be generated.

Below is the configuration for default storm control profile:

forwarding-options {

  storm-control-profiles sc {

    all;   <<<<<<<<<<<<<<<<<default config

  }

The storm control profile is setup without specifying any parameters related to bandwidth and burst-size associated with that profile. As a result system inherits the default bandwidth and default burst in the absence of any defined configuration.

Possible reasons :

• The traffic exceed the default bandwidth level

The default bandwidth level is 80% of the applied interface bandwidth.

The logs are usually seen if this bandwidth level is exceeded. So check if there was BUM traffic crossing the value set by checking the traffic rate on the interface.

• The traffic exceed the default burst level

Sometimes, storm control logs are seen even when the negligible traffic is seen on the interface. In that case, the burst could be the issue because the default burst is 1500 bytes.

So if the incoming burst exceeds 1500 bytes you will see storm control log message.

With the commands mentioned below you need to set an appropriate burst-size on the device.

root@EX4300# set forwarding-options storm-control-profiles sc all burst-size ?

Possible completions:

 <burst-size>        Burst size (1500..100000000 bytes)

Refer to the document below for the appropriate burst size calculation.

https://www.juniper.net/documentation/us/en/software/junos/security-services/topics/ref/statement/burst-size-rate-limiting.html

If the above step does not solve the issue, contact Support for a detailed analysis.