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Hierarchy Level


Configure the number of bytes of bursting traffic allowed to pass through a storm control interface. The burst size allows for short periods of back-to-back traffic at average rates that exceed the storm control level. If either the burst size or rate exceeds the limit, traffic will be dropped.

Storm control enables the switch to monitor traffic levels and to drop broadcast, multicast, and unknown unicast packets when a specified traffic level—called the storm control level—is exceeded, thus preventing these packets from proliferating and causing a traffic storm. Storm control can also shut down the interface in the event of a traffic storm.

The storm control level is a limit on bandwidth, which is configured using either the bandwidth-limit statement or the bandwidth-percent statement. The burst size extends the bandwidth limit so that sudden bursts of traffic do not cause storm control to drop packets or shut down the interface.

Because one burst size is not suitable for every traffic pattern, select the best burst size for an interface by performing experimental configurations. For your first test configuration, select the burst size limit by using one of the following methods.

The preferred method for determining the burst size is by using the following values:

  • bandwidth—line rate of the storm control interface (in bps units)

  • burst-period—allowable traffic-burst time (in milliseconds)

Best Practice:

We recommend you set the burst size value to the amount of traffic that can be sent over the interface in 5 milliseconds. For example, if your interface is configured with a 100 Mbps bandwidth limit, the recommended value would be 62,500 bytes. This value is derived using the bandwidth and burst-period, as follows:

  • Convert the bandwidth (100 Mbps) to bps units.

  • Multiply by the burst-period (5 milliseconds or 0.005 seconds).

  • Divide by 8 to convert from bits to bytes.

If you do not know the bandwidth of the interface, you can calculate the burst size using the maximum transmission unit (MTU). The burst size limit should not be set lower than 10 times the MTU of the traffic on the interface.

For more information on burst size calculation, see Determining Proper Burst Size for Traffic Policers.


If you do not configure the allowed burst size, a traffic burst in excess of the storm control level might cause storm control to drop traffic or to shut down the interface.


bytes—Burst size limit in bytes.

  • Range: 1,500 through 100,000,000 bytes

  • Default: 1,500 kilobits (187,500 bytes)

Required Privilege Level

system—To view this statement in the configuration.system-control—To add this statement to the configuration.

Release Information

Statement introduced in Junos OS Release 17.3R3-S7, 17.4R3-S2, and 18.1R1.