Cat6e/RJ45 cable problem (my Internets!1)

Well in short, I have a 30 meter cat6e shielded twisted-pair ethernet cable that doesn’t work. This cable was run through my house as part of a complete re-wire of the electrics, and like an idiot I didn’t test the damn thing before it was run. I’m not out of pocket by more than £10 or so at the moment, so at the currently I’m willing to throw some effort and money at fixing it without a re-run.

So, here’s what I know so far:

  1. It’s a 30m patch cable, pre-made, ordered online with a 20m and 10m patch. The other two work great.
  2. Plugging one end into my cable modem and the other into my laptop, the laptop reads “Media Disconnected”.
  3. Plugging one end into my laptop and leaving the other end unplugged occasionally led to it reading “Media connected”, but of course it couldn’t obtain an IP address or anything. I hate what this suggests, but this isn’t consistent at all. It happened maybe twice through about 10-20 attempts to get the cable to work.
  4. Looking at the connectors at each end neither seem dodgy or broken, and all pairs seem to be crimped ok.

What I’m after is a suggested list of things to try in order to get the cable working, short of getting a new length of it run by an electrician. I have monster amounts of slack cable at each end so cutting/re-crimping is not a problem. Do I need a cable tester? Is there a way to find where in the cable the problem is? Help me QT3, you’re my only hope!

I’m guessing that you’ve tried plugging it into a normal router and your laptop at the other end? I’m going to guess that it is a straight through cable and not a cross over?

Yes, I’ve tried plugging it into a router and a laptop at the same time, and it’s a straight-through rather than a crossover. At least, that’s what I ordered, it may well be a crossover that the cable modem or laptop can’t handle.
I bought a cable tester earlier today for playing about with - it was cheap and ever since I did the CCNA course I’ve wanted one anyway.

Here in the States, stores like Radio Shack and even occasionally Best Buy have UTP/Cat5/Cat6 termination kits for not too awfully much. I’m going to assume that if you’ve taken your CCNA course you know how to terminate them correctly or at least google that and do it correctly afterward.

That’s a long run of cable. Your tester will tell you which pairs are bad but regardless, you’re going to want to re-terminate if so. Replacing the entire cable would probably be more expensive than just re-terminating. You might even be able to borrow the crimp tool you need from work. This is what I would do, I’m loathe to throw out cables that are initially bad because, well, I just hate wasting cables.

I’m glad I’m not the only one, I’ve got a box of all my hideous, salvaged CAT5/5e/6 cable because I can’t bring myself to throw away good cable, even with spools of fresh new stuff laying around.

Definitely re-crimp the ends, and use a cable tester to figure out if there’s at least signal reaching the other end of each wire. It could be that while laying the cable it snagged somewhere and is frayed in the middle. If you know which wire(s) are bad, you could theoretically do a 10-mbps deploy using only 2 pairs of the cable, which is obviously less than ideal but better than nothing until you can run a new cable.

Or was just so sharply bent that it managed to break one of the strands–I’ve seen that happen before when the cable is pulled tightly around a corner rather than curved nicely.

I’m betting, though, that if the cable really is straight-through correctly, the problem is with the crimping. That’s the high-failure-rate part. Cutting the crimp off and redoing should solve it easily.

Yep, solid-core cable is especially susceptible to sharp-turn syndrome. Is the cable solid-core?

Also, if you do find that you’ve got a bad wire in the length somewhere, the only way to find out where it’s occurring is a tone and wand tester. It may be cheaper just to replace the length of cable than to buy one of those, especially for a single use scenario.

The cable is 4x twisted pair for sure. I was actually going to ask if there was a way to determine where in the cable the break has occurred; you say it’s a ‘tone and wand tester’? To Google!

  1. Plugging one end into my laptop and leaving the other end unplugged occasionally led to it reading “Media connected”, but of course it couldn’t obtain an IP address or anything. I hate what this suggests, but this isn’t consistent at all. It happened maybe twice through about 10-20 attempts to get the cable to work.

Shielded? Make sure that the shield is grounded on both ends.

9 times out of 10, it is the termination that is messed up. Make sure that your pairs are seperated to the correct pin numbers.

He’s referring to a cable toner. If you really wanted to find where a break was though, you’re looking at a cable analyzer instead. Prices are all over the place for analyzers, as these are sometimes used for high end repairs by professionals. With either tool though, you are rapidly approaching the cost of just replacing your cable.

EDIT: I realized you may not know what each tool does. A Toner Connects to a strand of cable on one side and generates a tone. You then go to the other side (or along the way) and hold the wand to the cable to note if it still “has tone.” Toners are great for checking if there is any connectivity at all, but not really suited for minor loss of signal problems. For me at least, I use it more on wiring blocks to locate where the correct cable is, not so much for tracing down a long length of cable. A cable analyzer does two things, it checks for correct termination of the cable, and it also checks for loss on the cable, and can be pretty exact on at what point loss happens (your mileage may vary, note that you get what you pay for when you buy an analyzer.)