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I have a network admin problem, is there a simple and minimally disruptive way to identify for a given network cable where it goes into the switch?

I have a lot of unlabelled cables and unlabelled ethernet sockets which ultimately connect to various switches I would like to be able to identify which goes where.

I have a cable tester but using that would involve un-plugging every end at the device and plugging each switch end into the other part of the cable tester, trying to find the correct end, I have to do this on my own so this would be a very tedious task and distruptive to the users affected.

Is there a cable tester that will produce a certain sequence of flashes in the switch to shew that it is the correct one, or is there some other way to identify the cable with less disruption?

Also can anyone recommend a device for attaching labels to cables that wont easily fall off?

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4 Answers 4

up vote 3 down vote accepted

Many good cable testers come with a probe. You plug one end of the cable into the tester and the separate probe unit makes a beeping noise that gets louder when you get near to the cable in question. Trust me, it saves alot of time, particularly if you have a lot of cables or (in my case) a rats nest of cables.

Here's the one we use: bytebros.com/bb_tester/TVR101001000.htm

As for the labels, it depends. If you use a heat-shrink label it'll be great, but it takes a while due to needing a heat gun as well, and is a bit of a pain. I normally use a dymo 5200 to print the labels in a way they can be wrapped around the cable, then put normal sellotape on top as i found the exhaust fan warm air from servers have make them peel after a while. You can get extra adhesive label rolls for it, but I've not tried those yet.

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+1, but also worth noting that the better your cabling, the less effective these are. We have CAT6 cabling throughout our building, and our cable locator is only effective next to exposed pairs, as opposed to it working fine with CAT5 cabling. –  Bryan Jan 25 '12 at 13:34
    
interesting. Last time i used it was either on stp cat5 or cat6. will check. –  Sirex Jan 25 '12 at 15:37
    
It might well be that we have an inferior cable locator :) –  Bryan Jan 25 '12 at 15:56
    
@Sirex Thanks for the cable tester suggestion I didn't know there were cable testers that could send a tone, very useful. –  Tim the Enchanter Jan 27 '12 at 10:59

With a cable tester you will still need to unplug devices. Least disruptive would be to ping everything, disconnect one at a time and see what stops responding. If anything vitally can't be disconnected you could possibly identify it by spamming the connection to a known device and watching the activity leds but that depends on it not being too busy already.

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You didn't mention what kind of switches you have, but if they're managed switches, they can probably assist in providing most if the information you're looking for. When I need to identify an unknown network drop, I usually use one of the following methods:

  1. Many vendors support discovery protocols that can be used for this purpose. Cisco's CDP and the vendor-neutral LLDP are probably the best known, but there are other vendor-proprietary protocols as well. They are often enabled by default. An approach I frequently use is to connect my laptop to a port I need to identify, and use a network sniffer to look for CDP packets. Among other things, CDP packets include the name and port of the switch I'm connected to. A good CDP filter for tcpdump or windump can be found here. You can just as easily install a sniffer on a connected PC and do it from there if you want to.

  2. If you can't disconnect whatever is currently connected to the port, or you can't use or install any software on it, another approach is to look on the switch for the host's MAC address. As long as the host is talking on the network, it should show up on the switch, and most managed switches will provide a way to get this information.

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For Labels I can highly recommend the Panduit LJSL5-Y3. You can run them through your laser printer, or write on them, and they 'self laminate' when you put them on the cable.

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