Broadcast Storm
This event is triggered when the number of broadcast frames per second is higher than the value configured in the Expert Thresholds setup.
A broadcast or data storm is excessive transmission of broadcast traffic in a network. This happens when a broadcast across a network results in even more responses, and each response results in still more responses, in a snowball effect. If network traffic reaches near 100 percent of the available bandwidth, all network traffic can be blocked.
A broadcast storm can also happen between routers when a broadcast packet is forwarded more times than it should be, or is generated repeatedly by a system in this case it may or may not include the duplication of the broadcast packet. The broadcast will eventually die because the hop count reaches zero, but in the meantime may saturate WAN links.
Although the function of a switch is to isolate traffic to the stations conversing, a broadcast packet must be propagated. These means that a broadcast storm can effect every station in the switched environment
Possible reasons for the event:
Catastrophic broadcast storms may be caused by failure of a device or NIC card. For example, if an NIC card repeats the same ARP request at a rate of several hundred times a second, the requests may be propagated around the network by other devices.
Broadcast storms can also be caused by misconfigured NetBIOS/NetBEUI servers or devices.