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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 39 Configuring Traffic Storm Control
Understanding Traffic Storm Control
Figure 39-1 shows the broadcast traffic patterns on a LAN interface over a given 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 39-1 Broadcast Suppression
The traffic storm control threshold numbers and the time interval combination make the traffic storm
control algorithm work with different levels of granularity. A higher threshold allows more packets to
pass through.
Traffic storm control on the Cisco 7600 series routers is implemented in hardware. The traffic storm
control circuitry monitors packets passing from a LAN interface to the switching bus. Using the
Individual/Group bit in the packet destination address, the traffic storm control circuitry determines if
the packet is unicast or broadcast, keeps track of the current count of packets within the 1-second
interval, and when a threshold is reached, filters out subsequent packets.
Because hardware traffic storm control uses a bandwidth-based method to measure traffic, the most
significant implementation factor is setting the percentage of total available bandwidth that can be used
by controlled traffic. Because packets do not arrive at uniform intervals, the 1-second interval during
which controlled traffic activity is measured can affect the behavior of traffic storm control.
The following are examples of traffic storm control behavior:
• If you enable broadcast traffic storm control, and broadcast traffic exceeds the level within a
1-second traffic storm control interval, traffic storm control drops all broadcast traffic until the end
of the traffic storm control interval.
• If you enable broadcast and multicast traffic storm control, and the combined broadcast and
multicast traffic exceeds the level within a 1-second traffic storm control interval, traffic storm
control drops all broadcast and multicast traffic until the end of the traffic storm control interval.
• If you enable broadcast and multicast traffic storm control, and broadcast traffic exceeds the level
within a 1-second traffic storm control interval, traffic storm control drops all broadcast and
multicast traffic until the end of the traffic storm control interval.
• If you enable broadcast and multicast traffic storm control, and multicast traffic exceeds the level
within a 1-second traffic storm control interval, traffic storm control drops all broadcast and
multicast traffic until the end of the traffic storm control interval.
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