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Tracing a network cable that is already connected to the system

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?

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.

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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.

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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. :)

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