Network monitoring with Ethereal

Wednesday, 24 December 2003, 10:06 AM EST

We all hope that our networks just do what they are supposed to but that often is not the case. Two systems that should talk to each other, don't; a network becomes saturated with traffic for no apparent reason; you need to know what some non-Linux device is doing. Ethereal may be the tool that saves the day.

For example, a few years ago I set up a a wireless link for a project. It was relatively slow (a real data throughput of around 300Kbps) but should have easily handled the traffic. Should have but it seemed saturated much of the time. On paper, everything was supposed to be fine. The link capacity was significantly more than the traffic. That was on paper.

There did seem to be a lot of lights blinking on the switch talking to the master radio but watching blinking lights to measure traffic is about as accurate as using your tongue as a battery tester. Starting up ethereal quickly identified the problem. There were a whole bunch of computers running some other operating system that liked to send broadcast packets over the network for such exciting events as a computer being turned on or the paper being low in a printer.

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