Simple CAT5 data run just will not work?

By robo_dev ·
I think I know the answer to this question, I'm just here whining......

I ran a simple 75 foot CAT5 data run, punched it down to a Leviton CAT5 module on each end, using 568A pair sequence, and it just does not work.

Got link light on both ends, but Windows XP status shows packets sent, but no packets received. So DHCP won't work, obviously and neither does PING or anything else.

Open pair, right?

I hooked up my Test-UM LanRover cable tester, it shows PASS and the capacitance measurement is normal. I double checked it with the cable tester, even trying to wiggle the cables in case it is a bad connection. Nope. This cable is perfect.

So my cable tester shows that it's good, from end-to-end, including the patch cables. Tried swapping patch cables, of course.

I get link light at both ends, have tested NIC and swapped ethernet router at other end.

The PC can ping a device on a switch attached directly to the PC, but not the router on the other end, which is pingable. Of course the PC cannot get a DHCP address either.

I plan to just re-terminate the CAT5 jacks....maybe something is not punched down cleanly???

This is a standard network, so I doubt I did anything stupid. Windows firewall is turned off, very plain-jane PC (security DVR).

If all else fails, I pulled a second run of CAT5 cable at the same time, so maybe there is cable damage from installing the cable???

I know, I know, I should have used wireless LAN!

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All Answers

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have you tried 568B ?

by CG IT In reply to Simple CAT5 data run just ...

while every cable guy will say 568A works, and it does, everything has to be wired 568A. So the biggest problem is all premade patch cords are 568B. so you hook up a 568A to a 568B what do you get? cross over cable. while there's link, maybe, and it will test fine with the lan tester, cross overs don't work on PC to switchports.

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Reponse To Answer

by DavidMBlackwell In reply to have you tried 568B ?

If both ends of a link are 568A, or both ends are 568B, then you have a straight-through. Doesn't matter if you use two straight through links, one using 568A and the other using 568B. The electrons don't care if the plastic around the wire is orange or green. You only get a crossover if one end of the same link is A and the other is B.

To address the original problem, EMI, faulty termination on the cable run, wire fault somewhere in the cable maybe it was damaged during installation? Since the equipment (I assume including the patch cables, otherwise add that to the list) all tested out before being connected to the cable run that is where I would be looking for the fault. It could have been damaged during the installation I've seen that happen many times in different ways.

Is this gigabit ethernet? If so, it uses all four wire pairs rather than just two. I've seen a few problems there that allow the initial negotiation to succeed but cause faults during transmission, or some devices that just won't step down to the slower speeds.

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Reponse To Answer

by CG IT In reply to have you tried 568B ?

As I said, all premade CAT5e patch cables you buy at a store are 568B. They are not 568A. If you make a home run 568A from a wall jack to the patch panel and use a 568B patch cable [premade bought from a store or dealer] you just created a cross over cable. I've seen it happen where the data cable guys cable the office 568A and the IT guys use premade patch cables and then scratch their heads on why it doesn't work. The contractor says they tested all runs ok, so not their fault, but failed to say they wired the entire office 568A so all those 568B patch cables the IT guys bought won't work.

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Reponse To Answer

by The DOBC In reply to have you tried 568B ?

Who is the idiot that keeps saying that one run punched 568A and a patch cable wired 568B will make a crossover? I think you need to re-read the books!

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Reponse To Answer

by CG IT In reply to have you tried 568B ?

I am...

a cross over is:
568A hook under/ right to left: brn/brnwht/org/bluwht/blu/orgwht/grn/grnwht on one side.

568B hook under/ right to left: brn/brnwht/grn/bluwht/blu/grnwht/org/orgwht.

you wire up the office 568A and buy your standard patch cable from the store and use it which is 568B wiring...what do you get?

that's a cross over cable:

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Reponse To Answer

by brucemc123 In reply to have you tried 568B ?

You're right... a crossover cable is 568A on one end and 568B on the other end. And a straight-through cable has the same wiring scheme on both ends so that all pin numbers are connected to the same pins on the other side (pin 1 to pin one, pin 2 to pin 2, etc.).

Computers transmit on the pair connected to pins 1 & 2 and receive on the pair connected to pins 3 & 6. Because of this, hubs and switches need to be wired to receive on the pin 1 & 2 pair and transmit on the 3 & 6 pair. But if you want to connect 2 computers directly to each other with one cable you need a crossover cable (568A on one end and 568B on the other) so both computers won't be trying to transmit on Pins 1 & 2 and receive on pins 3 & 6. The crossover cable connects the transmitting pair on one end to the receiving pair on the other end.

Most patch cables are 568B but I've seen 568A used (on both ends) and it works the same because as long as both ends are the same it's wired straight-through. And if you connect 2 straight-through cables (even if one is 568A straight-through and the other is 568B straight-through) you still send the signals straight through because what goes in on a particular pin number still comes out on the same pin number at the other end.

When in doubt... check Wikipedia. :)

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duplicate post

by CG IT In reply to Simple CAT5 data run just ...
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Does another computer work on same cable?

by greg.goss In reply to Simple CAT5 data run just ...

Does another computer work on the cable?
If not, verify a computer works plugged in at the very beginning of the run.
Keep moving back down the cable run (plugging in at each connection/junction point) until it no longer connects.

Are there florescent lights along the run? Motors? fans?

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Try A Crossover Cable

by brucemc123 In reply to Simple CAT5 data run just ...

Are you connecting two devices that need a crossover connection? Most modern hubs and switches are auto-sensing (automatic MDI/MDI-X configuration) but some have a special "uplink" port or even a manual switch when crossover is necessary and some have no crossover capability at all so a crossover cable is required. It's an easy thing to try just in case. A good explanation can be found on Wikipedia at:

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Reponse To Answer

by robo_dev In reply to Try A Crossover Cable

Thanks, At the far-end I've tried it with both the NIC itself and a switch that does auto-crossover. Since I get link on both ends and my cable tester says my pairing is correct, I think it's just a bad punchdown, damaged cable, or interference.

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