There's clearly something I need to learn about networking (well, there's tons I need to learn, but one thing specifically at the moment).

As I've mentioned before, I support a network in DC that consists of a five-floor building with many student apartments. The network consists of a less than ideal WRT54GL with Tomato (they give me zero budget here), but that connects to a series of switches on each floor that then goes out to drops in all the apartments/rooms.

Last week the whole thing went down, and they called me in to find out what it was.

In the end, I sussed out that there was something connected to the network that was killing it, and I assume that it was a router because when I connected with my laptop I was getting a different IP than I should have been getting. The legit router gives out addresses in 192.168.168.x, and the mystery router was giving out IPs at 10.0.1.x. This additionally leads me to believe that it's most likely an Airport Extreme.

My question (sorry for taking this long) is: how do I prevent this? What can I do to fix it?

I currently have disconnected an entire switch on the network, taking out an entire half of a floor because the people who installed this network didn't label a damn thing (what's up with that, anyway?). I'm going in tomorrow to try to figure out who the problem person is.