Fun Fact About OS X Networking
Running Mac OS 26.5.2 I’ve been using WiFi mostly on my Mac mini. Decided to connect a LAN cable to experiment with network speed and get two simultaneous input vectors going, LAN and WiFi.
(No multi NIC cards in the Mac mini)
EX: Trying to use AirDrop / Bluetooth / WiFi while running a heavy LAN process through the wired connection.
Using the router I’ve got two different VLANs running. One for WiFi and one for the wired LAN in the Home-Lab.
Very useful to keep guests out of the Home-Lab network.
The problem: To my surprise as soon as I plugged in the LAN cable both interfaces went dark.
This is very strange. Unplug the LAN and the WiFi comes back on-line.
Plug the LAN back in, WiFI goes dark, Ethernet goes dark again.
Repeat, again… OK, doing the same thing over and over again expecting a different outcome… we all know what that implies, right?
A little research reveals Apple’s thinking: “macOS is designed to automatically deprioritize or disconnect Wi-Fi to save battery and prevent network conflicts”
Nice save energy, run longer on batteries, save the world. That’s great, but my Mac mini is plugged into the wall, it is not on batteries.
Resolution: Under the system settings Network you need to adjust the interface order, supposedly.
(Three little dots at the bottom of the network list.)
System Settings -> Network
- Ethernet
- Wi-Fi
- Firewall
- Other Services
Then at bottom right you will see the “… v”. Menu button
Find the “Set Service Order…” menu item.
Then:
- Move the WiFi up above the Ethernet item.
- I had to reboot.
That still did not help get the interfaces back on-line. It should have. - Definitely a conflict in the DHCP or IPV6 settings.
- You could try switching IPV6 “OFF” or to “LOCAL” see if that helps.
- I ended up moving the plist files to the trash and let the Mac recreate them with both interfaces plugged in during the reboot.
Flush Corrupted Network Files:
Turn off WiFi and unplug the LAN cable
Go to directory: /Library/Preferences/SystemConfiguration/
Drag these three files into the trash:
- com.apple.airport.preferences.plist
- NetworkInterfaces.plist
- preferences.plist
Reboot
I plugged the LAN back in and activated WiFi before rebooting.
The system came up with both WiFi and Ethernet active.
Looking at the search order again in Networking “…v”
I now see the order as:
- Ethernet
- Thunderbolt Bridge
- WiFi
It appears the listing order was not the issue. The system must have been confused in the plist files.
Moving the plist files into the trash cleared things up upon rebooting.
The other bridge listings that were in the “…v” listing are gone. They should recreate as needed.
Conclusion:
I now have two working connections on my Mac mini:
- home-lab – vlan
- home network – vlan
Speedtest:
- between 886 Mvps – 984 Mbps
- Modem to ISP: 1.03 Gbps Download .03 above spec.
- Latency 15ms to the ISP.
- Upload speed 40.3 Mbps .3 above the service spec. Nice!