Custom iMac capping ethernet speeds to 100Mbps on 1gigabit network

[InVision]

I would have agreed with you if I did not see it with my own eyes. Figuring I don't understand the implementation of 10GB on the iMac but literally less than 100mbs on cat 5e 10ft cable and 980MBs on 200 ft cat 6a cable. Same everything else. Mind you I am using Cisco in our comm closet and looking at connections. My take if it is working don't fix it

M

 

[Bill_D]

I have seen the same problem, first with a 2011 Mac mini connected to an Apple Extreme router, and now with a 2018 Mac mini connected to a TP-Link AX50 router. The network connection speed would sometimes inexplicably drop from 1000baseT to 100baseT. Restarting the router or the Mac would temporarily correct the problem. I tried a couple of cat 5e cables, same result.

In both cases, connecting the Mac through an Ethernet switch eliminated the problem for good. If it is working ...

 

[VivienM]

That is pretty strange, I wonder if there’s something wrong with the 10Gb ethernet on the newer iMacs.

The 10 gigabit Macs, or at least the Intel ones, use the Aquantia 10GbE controllers. And Aquantia (now owned by Marvell) is basically the only option for a 'modern' end-user PCIe controller that supports 1000BaseT, NBaseT and 10GBaseT on copper. The super-high-end 'enthusiast' PC motherboards with 10 gigabit Ethernet onboard, the recent add-in 10G cards for NAS systems like Synology, etc also all use Aquantia. So do the rare non-server-focused PCIe 10G cards from the likes of TP-Link, Asus or Gigabyte. (For 2.5 gigabit, there's an Intel option and a Realtek option. And those are the two controllers you'll see everywhere.) 10 gigabit over copper is just this weird niche thing - people who do serious 10+ gigabit networking have been doing it for a decade over SFP+, but there's this small ecosystem all powered by Aquantia of 10 gigabit copper ports being thrown on a motherboard as a quiet upgrade to gigabit (and this ecosystem is so small that... good luck finding a reasonable switch for the other end).

But if you go and look in, say, the home lab community, you will see that Aquantia controllers seem to have a bad reputation. Not sure why. But when I've looked, I've gotten the impression that there is a clear preference for used Intel/Mellanox/etc SFP 1/10G-only cards over brand new Aquantia ones.

 

[ZMacintosh]

do you have a system report of your iMac (screenshots)? and one with the OWC dock connected? what kind of ethernet cables are you using? also, what internet bandwidth do you have? just because the iMac has 10-gigabit, doesn't mean your network speed will match....

 

[InVision]

Just a FYI

Well my 2020 iMac with the 10GB ethernet started acting up again on my 1GB backbone network. So far I have manually set ethernet settings, changed cables with new expensive ones. I basically am getting 100mb connection. I added a USB-C 10GB Ethernet and set to 1GB. Blazing fast. Best $12 I have spent. Time Machine to my Synology DS 220+ is fantastic.

M