We've a Cisco 2960e that services our VoIP phones and other things. I inherited it.

The question I have is the cut cables: there are about four network connectors that are cut about 1cm away from the end - making it nothing more than a physical connector. These connectors are paired with a working cable either on above or beneath.

I feel certain these connectors are some sort of flag; they can't be loop-backs as there is no cabling to do so (the connectors are cut and nothing else). There's no electrical connections: the only indicator the switch might realize is there is a physical presence in the jack - and I doubt that too.

The free ports are ominously quiet (of network traffic) as well: is this related? Are these connectors marking active ports?

UPDATE: I thought I was very clear; I don't know how I could have explained it any better. In any case, here's a picture:

Connections on Ethernet Switch

  • Can you post a picture? It's possible these were [at one time] just delivering power, not traffic. Something like this. – jscott Feb 23 '12 at 3:24
  • They don't look like that; it's nothing more than a connector with a stub of a cable left over from having been cut. The entire thing isn't much larger than a grape. There's no cable to speak of. – Mei Feb 23 '12 at 3:30
  • What do you mean "These connectors are paired with a working cable either on above or beneath"? Also, what do you mean by "The free ports are ominously quiet (of network traffic) as well"? An empty port won't show any network activity... naturally. – joeqwerty Feb 23 '12 at 13:00
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    Doing this on a PoE switch is just.. just... oh god – pauska Feb 23 '12 at 16:38
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    You may have thought you were clear, but when you describe something that is rather insane and has no best-practices reason for being what you're describing,...I'd ask for a picture if someone was saying they had a foal born with a golden spiraling pointy bone sticking out of its forehead. Just because it couldn't be what they're describing. Jus' saying... – Bart Silverstrim Feb 23 '12 at 16:40

Test the ports thoroughly before trying to use them. I can't speak for your predecessor, but one reason I've seen that done (with cut ends or empty crimped ends) is to "mark" bad or sketchy/lossy ports on a switch; it's a great way to see at a glance that a port should not be used.

  • A better way would be to label the dead ports "NFG" or simply "DEAD." – Ward - Reinstate Monica Feb 23 '12 at 6:06
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    ...why not just do what we do with cars that have those annoying little oil and engine lights? Black electrical tape over them? – Bart Silverstrim Feb 23 '12 at 16:41
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    If these ports weren't dead before plugging a cut cable in could certainly finish them off. I typically mark dead ports with an empty RJ45 head (one crimped with no cable attached) to avoid funky shorts upsetting the switch -- I would advise that over the "cut cable" plugs, ESPECIALLY ON A PoE SWITCH :) – voretaq7 Feb 23 '12 at 16:41
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    @BartSilverstrim I've seen that done - in "warmer" datacenters the glue melts off the tape and now you don't know which ports are dead and you have sticky bits of tape to clean up. (yuck!) – voretaq7 Feb 23 '12 at 16:42
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    Datacenters warm enough to melt the glue? NEED MOAR AC! – Bart Silverstrim Feb 23 '12 at 16:46

It looks like the cut connector is being used to identify that as a port that shouldn't be used. I use a similar method but always use a non terminated connecter and affix a label or tag to the connector.

In addition, just to be clear, the physical ports (and cables connected to them) aren't "paired" together. They may be configured as a LAG, but their physical adjacency is not an indicator that they're "paired" together in any way, shape or form.

One final note, plugging a host into an empty port and seeing no activity lights on the port is not a guarantee that there is no activity on that port or that the port is disabled, shut down, faulty, etc. The only guarantee would be to run a packet capture on the host connected to that port and verify whether there's traffic or not.

  • Actually, that's what I did: tcpdump (packet capture) on the specified port. No traffic. Oh - and I didn't expect the "pair" to necessarily be significant. It's probably just dead or flaky ports. – Mei Feb 23 '12 at 16:59
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    @David The ports are probably dead (either they were dead when they were plugged, or they died when that pigtail of wire shorted something it shouldn't have). I would replace these with blind plugs ASAP to avoid potential problems in the future though. – voretaq7 Feb 23 '12 at 17:05

I've done something similar in the past.

I've taken an empty RJ45 plug, and crimped it without installing a cable (otherwise you might damage the port on the switch)

This was done on a switch that had a shared port, (i.e. a logical port that had both a fibre and copper port). There was a fibre installed in the fibre port which was the uplink to the rest of the network.

This was done because a while ago, somebody (who shall remain nameless), once plugged something into the port, reconfigured the port to the required VLAN, and then wondered why the switch suddenly disappeared off the network.

The most important thing here (which I'm guessing your predecessor didn't do) is to document why you've done it.

All our admins review changes to the systems documentation, and the blank plug serves as a physical reminder, just in case.

  • +1: for documentation. At our organization we used crimped ends ("blind connectors") to fill disabled ports on switches the public can get their grubby little hands on such as in conference or training rooms. That way when they call complaining they "can't get the internet" - we can ask them if they removed a small plastic plug from the port first... – user62491 Feb 23 '12 at 21:36

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