2009-09-14

How I brought down Duke campus ethernet

This is a fun story I like to recall from time to time. This story is absolutely true.

Between my sophomore and junior years at Duke, they wired the entire campus for ethernet. (That's right, before then, it was all dial-up, baby. 14.4 blazing kilobits per second.) Every dorm room on campus was installed with its own personal 10Mbps CAT-5 jack, along with an individual coaxial cable outlet (now they could sell cable to each student directly, instead of just to the common rooms from which students would splice and run their own coax to their dorms for free — not that I would know anything about that, of course…). Duke was entering the digital age.

In a marvel of civil engineering, they managed to install this new jack in the most inaccessible location of every dorm room. So amazing was their work, that in my junior year room, which couldn't have been more than 20' wide, it required more than fifty feet of cable to go from the jack, around the edge of the room, to the desk on the opposite wall. The exact length of cable isn't that important, so long as it's noted that the maximum length of cable sold at the campus computer store was, in fact, 50'.

Now, in the mid-1990s, you didn't have a wide selection of networking equipment available at every local computer store. "Home networking" didn't even exist — it still took some work to get Windows 3.1 to even talk on a network. Today, you'd probably just go to Best Buy or even Wal-Mart and pick up a CAT-5 coupler for 50¢ and join two shorter cables. Back then, though, that wasn't feasible.

So, I bought a copy of Computer Shopper and found a deal on network cable, buying 100' at something a student could afford. When it arrived, however, I found I made a slight miscalculation — I bought bulk cable that did not, in fact, include any ends. I therefore bought the shortest, cheapest network cable available at the campus computer store (who could possibly have use for a three foot cable anyway?) and snipped off the ends with about a half foot of wire. I then proceeded to strip each of the eight individual wires from either end of my 100' cable (cut down to whatever length I actually needed for my room, probably something closer to 60'), twist them with the wires from my purchased cable ends, and wrap each connection with electrical tape. A quick test with a hallmate's multimeter confirmed that I wired each connection correctly, such that each contact passed straight through from one end to the other with no crosstalk to other lines. Everything seemed good.

I plugged in my cable and attempted to configure my network card. Unfortunately, every attempt I made seemed to get me nowhere. After about an hour of fiddling with settings, I decided to give up and head downstairs for a break.

On my way down, I heard a friend cussing up a blue streak, so I popped my head in to see what was going on.

"I'm trying to get my project done, but the @$%!?! network is down!"

"Really? How long has it been out?" I asked.

"About an hour now."

That's… quite a coincidence, I thought. Just to satisfy my own curiosity, I headed upstairs, where I left my network cable plugged in.

I pulled the cable out of the wall, and I heard from downstairs, "AAHHHH! FINALLY!"

I thought about this for a moment, then I plugged my network cable back in.

Came the cry from downstairs, "OH, F$*#! NOT AGAIN!"

I pulled the cable out.

"Geez, THANK you."

I pondered this for a few moments, debating the philosophical ramifications of great power and great responsibility. I then spent the next few minutes doing my best Homer Simpson impersonation, plugging and unplugging the cable as I chanted, "Net go up, net go down. Net go up, net go down." I then left the cable unplugged before my friend burst a blood vessel.

A short time later that evening, I began to wonder how widespread this effect was. I decided to call a friend of mine who happened to work at the campus computing help desk. The conversation went something like this:

Me: Hey, have you guys been having any problems with the network tonight?

Her (sounding very suspicious): Why?

Me: Because I think I can bring the network down.

Her: That was you?!

I told her about my cable and how my plugging it in seemed to be tied to my dormmate's inability to use the network. She exhorted me not to plug the cable in again, and said she'd call me back.

Later, I got a call from someone in the networking department.

"Not that I believe this is possible, but could you plug your network cable in for me?" he said.

"Sure." *click*

"Huh. And could you unplug it for me?"

"Yep." *click*

"You know, if I couldn't hear the click of the cable going in and out, I wouldn't believe it."

He then asked me about the cable, why I made it, etc. I told him that I just needed a longer cable to get around my room. He also asked me not to plug in the cable again and promised to be in touch.

I didn't plug the cable in again. I didn't want to bring down the network, honestly. I wanted to be able to use the network. The facts were, this cable didn't let me use the network, and it only prevented anyone else from using it. My goal was not satisfied. I had no problem not plugging it in again.

The next day, a couple people from the networking department came by and offered to trade me a pre-made retail 100' network cable for my homebrew cable of death. I was happy to do so.

I got a call within a day or two. Apparently, they tested my cable, and as far as they could tell, it was fine — it was wired correctly, nothing funny was going on with it. Near as they could figure, there must've been just enough resistance in my ghetto twist-and-tape connections to put just enough extra stress on their network to push it over a breaking point.

This theory proved to be true a couple months later, when I was called again from the networking department and asked if I had made another cable. It wasn't me this time; enough people had connected to the network that the tipping point had been hit again. Unfortunately for them, this time it wasn't a single extra-resistive cable, but the mass of normal cables that did it.

But I have to wonder if that cable isn't lying around in the Duke network lab somewhere, perhaps with a sign that says "evil network cable of death, do not use", as some kind of reminder about the importance of network infrastructure. Or if it's not so labeled, and if it might actually get used again.

1 comment:

Gavette's Blog said...

That sir....is awesome :)

-Furg