Cisco Catalyst 2950 Command Reference Manual page 437

Chapter 2 Catalyst 2950 and 2955 Cisco IOS Commands
The duration field could be n/a when a storm is still present or when a new storm of a different type
Note
occurs before the current storm ends.
Related Commands Command
storm-control
0L-10102-01
Description
Enables broadcast, multicast, or unicast storm control on a port.
Catalyst 2950 and Catalyst 2955 Switch Command Reference
show storm-control
2-409