Network disconnects when Ethernet is connected.

Give this a try: Reset NVRAM or PRAM on your Mac - Apple Support - 2-3 times in succession.

If still a problem boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and test to see if the problem persists. Reboot normally and check again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Hi Dmsuydam,

Thank you for posting in Apple Support Communities. From our understanding, when you connect to an ethernet cable, you no longer have any network connection, do we have that right? When you connect the ethernet cable, is Wi-Fi turn off or on? Does that make a difference? Have you tried with a different ethernet cable?

You mentioned this just started after updating, has your Mac been restarted since noticing this?

Log out, sleep, wake, restart, or shut down your Mac

Also, does this occur in another user or safe mode as well?

Set up users, guests, and groups on Mac

How to use safe mode on your Mac

Hope that helps!

Dmsuydam,

Thank you for that information. Have you checked to see if there are updates available for the macOS? Also, were you able to test a different cable? You can also try changing the order of the network ports that your Mac uses to see if that helps. You can put your ethernet as the top connection and the Wi-Fi as the second.

Change the order of the network ports your Mac uses

Take Care!

One thing I have observed with Catalina and Big Sur, is when I connect an Ethernet cable to the computer, it can not and will not access and available Wi-Fi networks. If I unplug the Ethernet cable, then my Wi-Fi connection is automatic (if it is set up properly). I would try a couple of things to help isolate the problem. These assume the problem is external to the computer. Try using a different Ethernet cable to see if the cable is defective. Try connecting to a different Ethernet port on your router/modem if one is available. Try resetting the modem. Go online to the internet provider's web site and use their link to test and check the functionality of the modem. If none of these things fix the problem, then I would assume that there is an issue with the OS and would consider reinstalling it. Good luck.

How are your two networks—the wired and the Wi-Fi networks—interconnected?

If there’s an IP router in the middle of that connection, then those two networks need to be using different subnets.

That you need an Ethernet connection to get to the printer implies there’s already something a little odd here, as the Wi-Fi network should be routable to the wired network.

I’ll assume the printer is using DHCP. If the printer is not using DHCP but rather has a manually-assigned static IP address, it’ll need to be coordinated with the DHCP server. (Some DHCP servers can detect this case without manual address coordination with the DHCP address pool, but far from all.)

This is most definitely a problem in Big Sur. My ethernet disconnects about once every few weeks, and happens to both my Satechi adapter, and my Apple ethernet adapter. It never used to happen on Catalina.

Hello Apple Support Team! I have been using my Mac Book Pro since 2017. Before upgrading to Big Sur 11.2.2 everything was ok with my LAN Network Port connected directly to my Internet Router. No Network problem. No Hardware changes at all. After installation of Big Sur 11.2.2, once or two times per day, I am experiencing a full network disconnection from the Operating System. All other devices (including a Windows 10 Notebook) keeps working ok in the same physical network. The network issue only happens on my Big Sur 11.2.2 Operating System. I am 100% sure that Big Sur 11.2.2 has a network problem. I have collected my "/var/tmp/sysdiagnose_2021.04.02_15-40-22-0600_macOS_MacBookPro14-1_20D80.tar.gz" file if you need to involve Software Engineering on this case. I would seriously recommend to follow up the case.

RAUL SOSSA SOSSA

IT Infrastructure Specialist

Costa Rica.