In-Depth

Networking Unplugged

What caused this problem the same time daily?

• By Kim Messner
• 10/01/2003

Then suddenly, after months of dealing with the same old network issues, the network began to shut down in the science building and library every afternoon around 4:30. The rest of the school would continue to run fine. By eight the next morning, the entire network, including the science building and library, would be up and running again! This was especially annoying for the teachers that chose to work in their offices or the library into the evening hours. It didn’t take long for the complaining to begin.

I examined every inch of the network, including the cabling and the various pieces of equipment, looking for what could possibly be causing this unusual outage. Since indoor Cat5 Ethernet connected buildings, I thought perhaps there was a minute crack in the cabling, and around 4:30 in the evening, when the sun started to set, condensation was entering this crack and preventing the signal from being passed on. This would explain why the network ran fine during daylight hours but not during the long, cold nights (at least to this newbie).

We didn’t have much money in the budget, so hiring a consultant to help me troubleshoot was a last resort. As I was near to pulling my hair out, I decided to try examining the entire length of the network and all devices on it one more time. Figuring two sets of eyes were better than one, I persuaded the school’s head of maintenance to join me.

We entered the basement of the building where most of our bridges and repeater lived. I pulled over a chair and stood on it to take a good look at the repeater one more time. That’s when the maintenance guy said, "Hey, where is this plugged in?" We followed the plug to an outlet in another room. The repeater was plugged into the same outlet as the water heater, which was on a timed circuit to conserve electricity. The circuit was set to switch off at 4:30 p.m. and trip on again at 6:30 a.m.

The evening maintenance people, when questioned, admitted that they unplugged the repeater from its outlet and plugged it into the timed outlet. They wanted to listen to the radio while working, and the repeater was plugged into the outlet they wanted to use. Needless to say, those folks were warned to not unplug any network equipment without my knowledge. And I wound up looking like a hero for solving the mystery of the network that shut down nightly!