Cisco CCENT / CCNA Certification Exam Tutorial: What Are Broadcast Storms?



Posted: Monday, August 06, 2007

by
The Bryant Advantage

The Cisco CCENT exam demands that you master the fundamentals of networking, and it doesn’t get much more fundamental than broadcasts! Every network has them, and every network administrator needs to be aware of what broadcasts are and their potential impact on network performance.

When a device on a network generates a message, it’s one of three types – a unicast, a multicast, or a broadcast. A unicast is a message intended for one other host; a multicast is intended for a group of hosts; a broadcast is intended for every host that can possibly receive it – and that’s where the trouble can begin.

Why? Because not every other host needs or wants to receive that message, and if “Host A" should not receive broadcasts sent by “Host B", we should configure the network accordingly. Everything we do on a network has a cost in performance, and if a host is regularly processing messages that it doesn’t need, that will result in a decline in that host’s performance. That decline may be slight, but if the host in question is receiving many unnecessary broadcasts, the decline in performance may be significant. Worse, the impact to our network as a whole may be significant as well.

Broadcasts tend to result in more broadcasts, and if hosts on the network continue to answers broadcasts with broadcasts, we end up with a broadcast storm. Broadcast storms start small, but just like a snowball, they can end up being very big – so big that normal network operations are compromised and/or prevented!

Don’t let the threat of a broadcast storm make you nervous about broadcasts, though. Broadcasts are part of a network’s normal operation, and we’ve got quite a few methods available to prevent these storms. We’ll discuss those in a future Cisco CCENT exam tutorial!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free Cisco CCNP Certification and CCNA Certification Exam tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.

You can also visit his blog, which is updated several times daily with new Cisco certification articles, free tutorials, and daily CCNA / CCNP exam questions!

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