72 Storm control
Storm control
Feature overview The storm control feature provides the ability to detect a traffic storm (broadcast,
multicast, or unknown unicast traffic received at a very high rate) and prevent
these packets from flooding other parts of the network.
When storm control is enabled, broadcast, multicast, or unknown unicast traffic
begins to drop when that type of traffic exceeds the configured rate threshold for
a particular port. The traffic resumes when the traffic rate returns to a level below
the threshold.
Storm control can be enabled or disabled per port; by default, this feature is
disabled for all ports. When enabled, storms are detected based on a configurable
rate that is defined as a percentage of a link's capability. The default rate is
five percent, which is used for all ports if another rate is not defined.
Additionally, unknown unicast (destination lookup failures) and multicast traffic
can be included in the storm control feature. Each can be enabled/disabled
separately per port and have a rate configured for that port.
Note that the hardware counters track multicast packets and unknown unicast
packets separate from each other (and separate from the broadcast packets). A
rate of five percent means that each traffic type will be allowed to reach that
threshold before storm control is applied.
The actual rate of ingress traffic required to activate storm control is based on the
size of incoming packets and the hard-coded average packet size 512 bytes (used
to calculate a packet-per-second rate), as the forwarding-plane requires pps
versus an absolute rate kbps. For example if the configured limit is 10 percent,
this is converted to ~25000 pps and this pps limit is set in the hardware. Users
will get the approximately desired output when 512 bytes packets are used.
Storm control
parameters and
defaults
You can view or configure the storm control feature with the following defaults
and parameters:
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