I’ve been using Thunderbolt 3 Dock TBT3-UDZ for the last 18 months with my older Intel MacBooks and Dell Precision 5540 running both Windows and Linux with no issues. Ethernet speeds using the built-in Ethernet port on the dock were receiving 920-940 Mbps (measured using iperf3 to my router).
HOWEVER, when I recently tried using the dock with newer MacBooks (MacBook Pro M1, M2, and MacBook Air M1) I started seeing terribly slow Ethernet speeds of 450-500 Mbps, also measured using iperf3 to my router.
As soon as I switch back to one of my laptops with Intel CPU, everything is working great. But with Apple’s M1 and M2 MacBooks, the Ethernet is actually slower than Wi-Fi.
Same setup, same Thunderbolt 3 cable (the cable that came with the dock), same Ethernet cable and port, and nothing else plugged into the dock (no video or other USB/Thunderbolt devices).
Any ideas what’s going on? Would a firmware update help?
Rebooting the MacBooks does not help. Rebooting the dock does not help. Rebooting router, switch, and other network devices does not help.
Details for OS and hardware of MacBooks experiencing slow Ethernet using TBT3-UDZ dock:
MacBook Pro M1 Pro running macOS Sonoma 14.5
MacBook Air M1 running macOS Sonoma 14.5
MacBook Pro M2 Pro running macOS Ventura 13.6.7
The dock works well on these laptops:
MacBook Pro Intel (2019) running macOS Monterey 12.7
Dell Precision 5540 running Microsoft Windows 11 version 23H2
Dell Precision 5540 running Linux 6.8.0 (Ubuntu 22.04)
Thank you for contacting Plugable support! Sorry to hear about this issue. I’d be more than happy to assist you.
To be fully up front, and unfortunately, at this time there is no solution for this behavior and a firmware update will not help in this case. The root of the performance difference occurs when using this dock with Apple M series processor based systems. These systems use an Apple provided Ethernet driver (built into macOS) that controls the Realtek RTL8153B Ethernet chipset in the TBT3-UDZ docking station. This problem should affect any product using this Ethernet chipset as well to my knowledge, so it is unfortunately a widespread issue across the industry.
The Apple provided Ethernet driver being used is not optimized for newer M series systems, the driver is an emulated driver vs a native driver. So for example, older Intel Macs (and x86/x64 Windows or Linux based PCs) do not experience these kinds of issues because the driver was written for that platform, but for the newer M series processors the driver is being emulated to work on the new M series platform (Arm) and this can cause performance losses to occur. At this time Realtek does not offer a stand-alone driver to install that is optimized, currently only the Apple provided driver is available.
You should be able to verify this by going into the Mac System Report → Hardware → Ethernet and look at the driver field for the Ethernet chipset (“USB 10/100/1000 LAN”). You should see for the Realtek Ethernet in the TBT3-UDZ it’s using the emulated driver:
Typically in cases where users encounter speed issues the best workaround would be to bypass the TBT3-UDZ Ethernet with a external USB Ethernet adapter (connected to one of the dock USB ports) that does have a native macOS M series driver available. As an example, the newer Realtek RTL8156B 2.5Gbps Ethernet chipset runs from the native driver (com.apple.driver.usb.cdc.ncm) and offers full performance - an example of this would be: https://plugable.com/products/usbc-e2500
It is also possible that Realtek or Apple may be able to release an updated native driver for the RTL8153B chipset, but I do not have any estimate for if or when that may occur. My apologies.
Please don’t hesitate to let us know of other questions.
Thanks again for contacting Plugable support and best wishes!
Thanks for the detailed response. Kind of what I was afraid of.
I was able to confirm that with another USB-C Ethernet adapter plugged into the hub, I’m able to receive high transfer speeds over the Gigabit Ethernet port.
You’re most welcome for the help and my apologies for the bad news.
I am at least glad to hear you are able to see higher speeds using a separate Ethernet adapter. If you need anything else of course please do let me know.
