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, and 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 on the
Cisco Nexus 3000 Series switch 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 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 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 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 multicast traffic until the end of the interval.
By default,
Cisco NX-OS takes no corrective
action when the traffic exceeds the configured level.