Conflicting symptoms on a "bad" cat5 cable

[Guest_imported]

Weird problem. I have a Cat5 cable, about 35meters long, going from one room, out a wall, along about 15 meters of outside wall, back into another room (this is PVC coated, not Plenum). For over a year, I had no problems.

Starting 3 days ago, the nic one end is plugged into shows a Green 100MB light, and the switch its plugged into on the other end shows a 100MB link light as well (all normal). However, there is no data connection. Even simple pings no longer register. I've tested the cable by placing the same system on another cable 8ft from the switch and it works fine, but back onto the original cable and it doesn't (though according to both the switch and the nic, its healthy). The cable is not long enough to have both ends in the same room for testing (its about 15 feet too short), and removal from the wall would be rather burdensom (its rubber cemented in basically). Any ideas what may or may not be wrong with it? I visually inspected the length of the cable, both the inside and outdoors sections, and found no obvious signs of damage.

The only clue I have is that it runs about 4 feet from the electrical box of the house, but it hasn't been a problem before for the past year and half. Any ideas or suggestions would be most welcome.

S.G.

 

[MWM]

Without test equipment you are forced to verify things by substitution.

If I understood it correctly, you have a known-good setup with two machines directly off the switch. But when one of them is moved to the far end of a cable, you get link lights but no upper level response.

First a link light is only a sign of the most basic electrical connection, not a data connection. A link light does not require all pairs to be good.

Second, ping actually has more than one flavor: it can bring back more information that simply, "Timeout," or, "Host unreachable." You might check the web for some ping programs (like, Super Ping) that return more information.

Then you can know more. If, however, your pings are not returning at all ...

Did you verify the simple things, like IP addresses (otherwise, a ping will just go into thin air)?

Can you string a second, temporary cable in the hallway?

This sort of confusion is where test equipment pays for itself.

Yours,
Mike

 

[Guest_imported]

Yup, you got it right (actually, its 7 computers with only 1 on a bad wire, but numbers don't really matter).

On ping I'm just using basic ol' ICMP Echo Request. Haven't tried Super Ping or linux ping (udp) since I'm not getting anything back. I've verified configuration & settings in triplicate, so I'm positive the problem is the wire. I'm going to try the secondary wire in the hallway next.

I have a basic cat5 testing tool, but you need both ends in the tool. Sadly I don't have the tool that comes in two parts and is wireless to test each individual wire. I'll see if I can get my hands on one of those. Thanks for the suggestions!

 

[Guest_imported]

You say the two ends of your existing "bad" cable are short by 15ft if you try and bring 'em together... Check out a 5m patch cable with your tester and then link your bad cable to the patch with a straight through adaptor. Now you should have the two ends capable of meeting at your tester.

Check to see if the gold coloured RJ-45 plug contacts look tarnished. If yes, you could try cleaning them or maybe crimp a new RJ-45 on the end(s). Look very carefully again at the cable just to see if Mrs Mop hasn't inadvertantly sliced into it with the hoover! Could you have got a rodent problem in that wall?

Good luck!


ROGER - GØAOZ.

 

[Guest_imported]

Good idea Roger, that's exactly what I ended up doing

Funny thing is is that it tested all good. So then I tested it by pinging from the system on the affected wire to any other system on the switch. All lights on the switch showed activity. HOwever, when I tried to ping the system on the bad cable, all lights showed activity on the switch EXCEPT for the one with the bad cable, so I'm guessing its one of the wires or contacts on a receive wire. I tried recrimping, but that didn't do anything, so I'll probably try reterminating both ends and see if that helps.

 

[Guest_imported]

Has the "bad" cable suffered a lot of bending, twisting or perhaps been run over by a trolley or piece of equipment perhaps...? Not sure what sort of tester you have, but maybe it cannot easily determine incorrect impedance, for example. Could some of the wires within the cable have become untwisted, etc., due to constant movement? It is most unlikely that your electrical junction box could have any effect upon the cable at a distance of 4 feet, but has anything been attached to that wall, holes drilled into it, etc?

If re-terminating both ends doesn't cure it, I'm afraid it looks like you'll have to burrow into the wall and fit a new piece of cable...


ROGER - GØAOZ.

 

[rgroulx]

I've seen this problem before when the NIC and switch have problems negotiating auto & manual speed/duplex settings. Have you tried manually setting port configs on the switch?

 

[davemiller]

If your speed increased from 10 MBPS to 100 MBPS, and PINGs now fail, your wiring is quite likely the cause.

Regarding test gear be sure any tester you use can test not just CAT5E, but can test throughput at 100 MBPS, anything less isn't going to be complete.

100 MBPS requires complete spec components end to end, ie; modular wall jack(s), distance not to exceed 100 meters, wiring CAT5E minimum, closet and/or switch patch panel and cabling meet CAT5E minimum, and use of punch-downs at the wall jack or closet need to be properly twisted and terminated (avoid crosstalk). If the wire is shielded it must be grounded at one end.

Meanwhile setting your link speed back to 10 MBPS at one or both ends, starting with the PC, will get you back up and running until you resolve the cabling.

 

[davemiller]

Oh - and avoid running any wire near Fluorescent lighting
at all costs! Fluorescent lighting causes severe EMI.
When in doubt correct all possible conditions on your present scenario, and then turn off all lights and re-test the connection.

 

[Guest_imported]

I'll try the manual setting, but I'm not sure if I can (we're talking a home network using an 8-port Linksys auto-sensing switch, so I don't think it has any user-available settings to speak of). And actually the speed has always been the same, the only reason the speed increased was when I changed out the network card (original was a 10MB 3com ISA card, and I replaced it with a 100MB 3com PCI card, but both suffered the same problem).

I tried retermination (removing about 1 foot of cable from each end) and it didn't solve the problem. Doesn't seem to be near (within 5 feet) of anything that would cause interferance (except the electrical box of the house, which never caused a problem before). And I can't seem to find any section that has been subject to kinking, being stepped on, etc.

I guess I'll just have to try replacing the wire. Thanks for the suggestions & help though! I was certainly hoping it wouldn't require replacing, but it looks as if it may.

 

[askreno]

This post is probably too late but..

Have you tried swapping ports on the switch? Sometime switch ports fail or just become disabled. Another idea is to power off the switch entirely - just to reset all the port and the mac table.

Other possibility is to swap the actual computer on the "bad" cable to rule out a bad configuration. Perhaps an IP conflict of some kind is responsible.