Understanding Storm Control; Default Storm Control Configuration; Enabling Storm Control - Cisco 2950 - Catalyst Switch Configuration Manual

Configuring Storm Control

Understanding Storm Control

A packet storm occurs when a large number of broadcast, unicast, or multicast packets are received on
a port. Forwarding these packets can cause the network to slow down or to time out. Storm control is
configured for the switch as a whole but operates on a per-port basis. By default, storm control is
disabled.
Storm control uses rising and falling thresholds to block and then restore the forwarding of broadcast,
unicast, or multicast packets. You can also set the switch to shut down the port when the rising threshold
is reached.
Storm control uses one of these methods to measure traffic activity:
•
•
The thresholds can either be expressed as a percentage of the total available bandwidth that can be used
by the broadcast, multicast, or unicast traffic, or as the rate at which the interface receives multicast,
broadcast, or unicast traffic.
When a switch uses the bandwidth-based method, the rising threshold is the percentage of total available
bandwidth associated with multicast, broadcast, or unicast traffic before forwarding is blocked. The
falling threshold is the percentage of total available bandwidth below which the switch resumes normal
forwarding. In general, the higher the level, the less effective the protection against broadcast storms.
When a non-LRE Catalyst 2950 switch running Cisco IOS Release 12.1(14)EA1 or later uses traffic rates
as the threshold values, the rising and falling thresholds are in packets per second. The rising threshold
is the rate at which multicast, broadcast, and unicast traffic is received before forwarding is blocked. The
falling threshold is the rate below which the switch resumes normal forwarding. In general, the higher
the rate, the less effective the protection against broadcast storms.

Default Storm Control Configuration

By default, broadcast, multicast, and unicast storm control is disabled on the switch. The default action
is to filter traffic and to not send an SNMP trap.

Enabling Storm Control

Beginning in privileged EXEC mode, follow these steps to enable storm control:
Command
Step 1 configure terminal
Step 2
interface interface-id
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
22-2
Bandwidth based
Traffic rate at which packets are received (in packets per second) (available only on non-Long-Reach
Ethernet [LRE] Catalyst 2950 switches)
Chapter 22
Purpose
Enter global configuration mode.
Specify the port to configure, and enter interface configuration
mode.
Configuring Port-Based Traffic Control
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