Network speed inconsistencies

Discussion in 'Mac OS X Server, Xserve, and Networking' started by kimjohnsson, Jun 12, 2017.

  1. kimjohnsson macrumors member

    Aug 13, 2013
    I have an irritating speed issue in my home network.

    My network has gigabit switches like this:

    Switch 1 <- Switch 2 <- iMac 1, iMac 2
    Switch 1 <- Switch 3 <- Mac Mini 1, Airport Extreme
    Switch 1 <- Mac Mini 2

    All Macs are manually set to 1000BaseT in their respective network settings, and that seems to be working.

    To test the network speed, I’m running Speedy Net on the four Macs, and any traffic not crossing the Switch 1 / Switch 3 boundary goes up to about 700 Mb / sec. If I cross the boundary between those two particular switches, I only get 87 Mb / sec. Copying large files from Mac Mini 1 to Airport Extreme "within" Switch 3 is consistently quick as well.

    Switch 1 is in the basement, Switch 2 is in the study and Switch 3 is in the living room. The cable between Switch 1 and Switch 3 is shorter than between Switch 1 and Switch 2. Mac Mini 2 is upstairs and has the longest cable between it and the switch. Even the longest cable isn’t particularly long, 20 m tops.

    I’ve swapped out both Switch 1 and Switch 3 for a couple of other ones and tried different cables and ports (not all combinations). Currently I’m using three brand new NetGear switches, but my previous Switch 3 was a Zyxel, and according to its led color, the port connected to Switch 1 was only operating at 100, so that seems to be the problem, although I can't understand why.

    What could be wrong here?


  2. belvdr macrumors 603

    Aug 15, 2005
    No longer logging into MR
    If switch 3 is only connecting at 100Mb, and they are both gigabit switches, then you have a cable issue. Gigabit uses all 8 wires (4 pair) so if there's a short or broken wire, it could downgrade to 100Mb as it only uses 4 wires (2 pair).

    There are products that will test an Ethernet cable and tell you what's wrong, but they are fairly expensive. You could also attempt to redo the ends of that cable or jack that leads to switch 3.
  3. kimjohnsson thread starter macrumors member

    Aug 13, 2013
    OK, thanks for the info. However, I just did some experimenting; I bypassed Switch 3 entirely and connected Mac Mini 1 directly to the wall where Switch 3 was previously connected. Now I get gigabit speeds to the other Macs, so the problem is not in the wall, apparently. So I guess this narrows things down to either the switch or the cable between the switch and the wall, but both of these have been swapped out for alternatives, so I don't think it's either of those.

    That leaves a bad wall contact, I suppose, and the currently connected cable just happens to connect the way it should.

    I'll try to keep it connected and rearrange the other cables and see what happens.


    --- Post Merged, Jun 12, 2017 ---
    OK, it works now. Don't know if it was a bad cable contact or just a bad cable, but now it works and I'm not going to touch it to find out.



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