I plugged in my notebook via cat5e patch cable to a terminated jack (we had some consultants do the runs), I get no signal not even an indication that it is connected but has no DHCP. I try another cable and it still fails. After about 5 minutes I try another cable and it finally works. I take the cable that was not working and try it and now it works? What is going on?

Network drops are as follows:

office rj45 jack>cable going to server room>patch panel>3 ft cat5e cable>network switches


  • 1
    Maybe the jack is badly terminated, and by trying the different cables you jiggled port in a way that made a loose connection temporarily work? – Zoredache Aug 6 '10 at 21:41
  • Make sure your notebook port doesn't deactivate to turn off power. My dell laptop deactivates the port when it is unplugged to save battery power. The port may wake up when it sees a connection. – USACASD Aug 6 '10 at 22:37
  • just to clarify, not only was i not getting an ip address, i was getting 0mbps as the link state so it did not even know it was plugged into anything live. – user8256 Aug 7 '10 at 22:13

The most likely cause is the physical connections, almost certainly on the punch block(s). It may also be cause by incorrect pairing of the cables, which is common when inexperienced people do the work. This is why you should insist all cabling is properly tested and certified. As for the remedy, I'd have the cabler back with his tester in hand.

  • This. Having wired up an office, a tester is invaluable. Even a well punched block can sometimes pull out from the stress on the cable when put back into the wall. – Tyler K Aug 7 '10 at 6:27
  • i think it is time for a jds validator or a fluk linkrunner pro. that is my next step, i need it for many other clients contracts so it is a justified write off.gd – user8256 Aug 7 '10 at 18:27

There could be many causes: the jack could be dodgy (bad punch, loose jack, bent bars, ...) or you could simply have two less-than-perfect cables.

If it doesn't work with those two cables and does work with everything else: dump the bad cables.

If behavior is inconsistent, you can measure out the patch..


Along with drop length (as well as overall cable length including the tested patch cords), there may also be a remote chance of RF interference (cable length will also play into anti-RF performance). First stop might be comparing the patch cord lengths to see if there is any pattern which might support/lend to a RF situation (which is typically very tricky).

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