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
traffic exceeds the configured level.