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Some remodeling was done while I was away from work, and I'm left with several unlabeled cat5 cables that are terminated with RJ45 keystone modules. On the other end, all of the cables are terminated at the patch panels in the server room.

Some of the cables are connected to the switches and are active data lines. I can verify the lines are active by plugging a laptop into the keystone modules. The DCHP server assigns an address and I'm in.

During my attempts to trace the lines using a toner and probe, I noticed that the lines that are active have a very weak tone signal. It is so weak, I can't trace it. The other lines, however, I was able to trace without any issues. Anyone know why the signal is so weak? Is it because the line is active and data packets are watering down the toner's signal?

masegaloeh
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    Do you use managed switches? If so then forget about using the toner for active lines. Plug your laptop into them and look for it's MAC address in the switches MAC address table and then trace the cable from that port. – joeqwerty Jan 06 '15 at 20:37
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    @joeqwerty likewise, you can compare your MAC address against your DHCP entries and resolve a hostname. Boom. all ports mapped. – Get-HomeByFiveOClock Jan 07 '15 at 01:50
  • Run a script to export all devices MAC from domain and switches, then do a comparison. Done. – Root Loop Feb 13 '16 at 04:28
  • That's all well and good... until you're trying to fix a bad wire and you have no idea where it is in the closet because the two middle wires are good. The correct answer below is by @Gabriel-King, where you swap two of the toner wires. – Brain2000 Mar 08 '18 at 17:34

4 Answers4

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During my attempts to trace the lines using a toner and probe, I noticed that the lines that are active have a very weak tone signal. It is so weak, I can't trace it. The other lines, however, I was able to trace without any issues. Anyone know why the signal is so weak? Is it because the line is active and data packets are watering down the toner's signal?

Most of the cheap tone generators/tracers won't be able to properly tone out a cable that is "active" (plugged into a switch with an active connection).

Some of the nicer ones will, such as the Fluke IntelliTone Pro 200.

From their site:

Modern network devices use aggressive termination schemes for cables connected to their ports. While this termination reduces noise and crosstalk in the cable, it can also absorb an analog toner signal, making the connected cable impossible to detect with an analog audio probe.

Otherwise, you could see if your toner allows the generator to change cable pairs (some with wire clips would allow this, but you'd have to cut and reterminate the cable after).

My suggestions for the ones that you want to trace that are plugged in if you don't have a more advanced toner like the Fluke one would be to plug your laptop in and out while a co-worker watches the front of the switch. Simple, effective.

For tracing a live server back to the switch, like Joe said, if it's a managed switch just check which port it is connected to in the mac forwarding table. If it isn't a managed switch then figure out some downtime and do like I said above. :)

TheCleaner
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Another quick and dirty solution is to get a partner to take a laptop and repeatedly plug and unplug into keystone of the cable you are trying to trace. While he is doing that, look at the switch(es) for the link light that keeps going on and off.

If you don't have a partner, take a picture of the link lights with the laptop unplugged with your cell phone. Then, plug in the laptop and compare the lights to the picture you took to see which one is lit.

One other suggestion if you are using managed switches. Many switches will give you uptime statistics for each port. Plug in a computer to the cable you are trying to trace and log into the switch(es) to see which port has an uptime of a minute or two.

pooter03
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If you use split pairs on your toner, it can trace through an active switch port. For example, put one of your toner leads on blue/white-blue, and the other on brown/brown-white, and you will get a tone. That is because the electrical circuit is not completed on the blue pair. Works like a champ.

Gabriel King
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  • This is the correct answer. I modified the toner connector to go on the side pins instead of the middle pins. Works beautifully now!!!! Can I upvote you 10 times? – Brain2000 Mar 08 '18 at 17:33
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Fluke makes a toner that will trace live lan cables plugged into a switch. It's called intelliprobe lan 200. However it only works on home runs and not thru hubs, poe's or small switches in a home run.

Randall
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