The Magical “No HTTP-traffic” CAT5 Cable

Now I’m really starting to doubt myself. For 2 weeks have I been troubleshooting a Vista machine that just got connected to the network. I’ll start to from the beginning;

2 weeks ago we had a contractor add a double CAT5 cable between two building so a computer in the second building would get internet access. The contractor finished his job, and I was about to go get some patch cables to wrap up the gig when I get a call that one of the teachers (the location is a school) had already scrounged up some cables, connected the computer to the wall outlet and the other outlet to the switch, but he couldn’t get it to work.

I went over without any patch cables thinking this would be an easy task, he probably connected the patch cables to different outlets in both ends. When I get there I notice that he used some of those old style cables, you know, just a crimped on 8P8C connector at the end of the cable, no dust cover, no injection molded strain relief. Determined to get this to work fast I first check his connections, no luck there, he actually used the green outlet in both ends (Lexcom outlets). Thinking that the contractor might have forgotten to fault-check the cables (Lexcom seldom has any connection problems so sometimes the rookies tend to get lazy), so I switch over to the red outlets, still no luck.

I then proceed to blame the switch, it was a cheap dumb desktop model and I knew it has had some problems before that could only be solved by a hard reset. Luckily I had another dumb 8 port in my car (Zyxel, very nice gear for this kind of things) that I knew worked so I switched it out. Suddenly the connection went live, and I thought I had finally found the problem, not as easy as I thought, but relatively simple and now I had fixed another problem I knew was just waiting to happen (the switch).

But, when I get over to the computer in question, things get really weird. The computer gets a physical connection (blinking lights on the NIC), and Windows even manages to get an IP. I open IE8, and it finds Google just fine, but hangs midway through. I try pinging our HQ’s gateway, no problem there, I then try to ping, and it resolves the IP just fine, but then hangs. I then remember that our network doesn’t allow outgoing ping requests for some reason (I didn’t design it), so no worries there either.

After about an hour of fiddling (it’s getting late on this cold Friday evening), I give up and decide to try again on Monday.

I go back on Monday morning with a pair of fresh CAT5 patch cables, I thought that since the old ones were a tad short anyhow I might as well replace them, one less thing to worry about.

I get there, and the building with the computer is locked, so I switch the one by the switch and hand the other one to the enterprising teacher, saying that “this will certainly not fix it, but I’ll be back in a couple of days when I’ve had some time to think this through”.

During the next one and a half week I spend a lot of time googling this problem and consulting guys with more Vista experience than me. This led to all kinds of weird theories, Group Policies that weren’t right due to the fact that the machine was on the same VLAN as the domain controller but not in the domain due to the home license. I didn’t buy this so I never looked into it.

Now, fast forward until today, and I went back there armed with a Knoppix CD to make sure it wasn’t a hardware related issue. The teacher had changed the network cable, but he wasn’t there so I couldn’t talk to him. I booted into shell, everything looked alright, I started Lynx, and google loaded just fine. This really started to annoy me, so I took a copy of the ip-settings from Knoppix and booted into Vista to do the same there so I could post them on the web in case I was going blind or something.

And wouldn’t you know it, the damned thing worked. And the only thing I had done to fix it was changing to patch cables.

Ladies and gentlemen, I give you the straight CAT5 cables that passes DHCP requests, pings and DNS look-ups, but not HTTP traffic.

Ain’t life grand! 🙂

Categories: Tech

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