I've connected a MBP 2017 (Big Sur) with an Alienware 17 R5 (Windows 10), both of which support Thunderbolt 3. I'm using a "Thunderbolt Bridge" connection.
The cable is an intel certified CalDigit Thunderbolt 4 cable which is backwards compatible with Thunderbolt 3:
Mac connection:
PC connection:
I have run connection speed tests on both the mac and the PC using LAN Speed Test. Here is the LAN Speed test results on the mac:
And on the PC:
The LAN test client on the mac is connecting to LAN Test Server on the PC. On the PC it's doing a file write to a shared folder on the mac. In both speed tests data transfer from the pc to the mac is very slow, but reasonably fast in the other direction.
I've configured a static IP address for each connection.
I've tried:
- Rebooting both machines after the cable has been connected
- Setting net.inet.tcp.tso=0 hinted at here and here
- Disabling all firewalls on both Mac and PC
- Making sure PC BIOS and drivers are all up-to-date
- Disabled all other network connections on both PC and mac
- Set the priority of the Thunderbolt Bridge higher on the mac
Update: I tried a third PC, an Intel NUC. The thunderbolt connection worked between the Alienware and the NUC, and the Mac and the NUC. For some reason the connection doesn't work between the Alienware and the Mac. Have double-checked for software updates, and everything seems to be up to date.
1 Answer
It appears this issue was introduced with Windows 1903 when connecting to some devices. A workaround is to enable "Allow other network users to connect through this computer's Internet connection":
After enabling this I then had to re-enable DHCP for my main internet connection. References:
