I have a network split over several small offices. At one office, serving about 30 users, I'm seeing some machines getting much better network speeds than other. I have a patch panel plugging into two unmanaged switches, each of which connect to a port on a managed Cisco switch, which converts to fiber going back to my main office.

When I do a speed test on a PC plugged into port 230 on my patch panel, which plugs into Switch A, I get 90MB down. The PC on port 231, plugging into Switch B, gets inconsistent speed, ranging from 3-30MB down. Upload is similarly inconsistent. I've tried switching Port 231 into Switch A, but it gets the same results. Also, other ports from my patch panel are getting similarly split results, independent of the unmanaged switch that they plug into, some between 75-90 down, others spiking from 3 up to 30 and back. I've tried using one laptop in both the fast ports and the slow ports, and the laptop's results mirror the prior results.

I've tried doing a packet capture, but I don't really know what to look for on this problem.

Anyone have any idea of where I can look to figure out what the problem might be?

EDIT: Well, I went to trouble shoot and the problem stopped. So...the mystery remains, but the problem does not. If I wasn't short staffed, I'd spend more time looking into this, but unfortunately, I don't have the luxury. Thanks for the help, everyone!

  • Have you tried the laptop directly on the switch ports or on the client ports?
    – Zac67
    Commented Jul 7, 2017 at 17:39
  • Only on the client so far. I'll give a direct connect on the switches a try and see if I can recreate the problem from there.
    – Tim N
    Commented Jul 7, 2017 at 17:48
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin
    Commented Feb 19, 2018 at 5:50

2 Answers 2


This sounds like a cabling problem. The cabling seems to work, but it is just bad enough to cause a lot of retransmissions. You should look closely at the test results that your cable installer provided. You should be able to get the installer to fix any problems.

  • In addition, cable problems should surface as port errors, ie. indicators such as FCS error, giants, runts should be increasing.
    – Zac67
    Commented Jul 7, 2017 at 17:38
  • None of the cabling has changed; these work stations all had perfectly fine internet until earlier this week. I did have a fiber converter blow out, and I replaced it. But the converter in question is a midpoint, upstream from my Cisco managed switch. I'll try replacing that with a new unit, and check my fiber to make sure it isn't kinking anywhere.
    – Tim N
    Commented Jul 7, 2017 at 17:51
  • Did you look at the test results from your cable installer that installed the new fiber?
    – Ron Maupin
    Commented Jul 7, 2017 at 17:57
  • There wasn't any new fiber, just a new fiber/ethernet converter. My standard tests didn't show any abnormalities after installation. Clean packet transition on my p-cap and no errors reported on the upstream switch.
    – Tim N
    Commented Jul 7, 2017 at 18:03
  • I mean all the tests to determine if copper or fiber cabling passes the test suite for the category or fiber class. For example copper cabling requires a whole suite of tests, such as frequency, insertion loss, NEXT, PSNEXT, FEXT, ELFEXT, PSELFEXT, return loss, propagation delay, delay skew, balance, longitudinal conversion transfer loss, etc.
    – Ron Maupin
    Commented Jul 7, 2017 at 18:07

Check that duplexing is setup correctly on both switches.

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