After updating my iMac to Sonoma, I cannot get to the internet using my ethernet connection

Not on OS14 now, but have tried to interpret my old advice from Sys Prefs to Sys Settings...

System Settings>Network, click on the little gear at the bottom next to the + & - icons, (unlock lock first if locked), choose Set Service Order.

The interface that connects to the Internet should be dragged to the top of the list.

System Setttings>Network>choose interface>Advanced>Proxies Tab, make sure none are set, like for HTTP & HTTPS.

System Setttings>Network, unlock the lock if need be, highlight the Interface you use to connect to Internet, click on the advanced button, click on the DNS tab, click on the little plus icon, then add these numbers...

8.8.8.8

8.8.4.4

1.1.1.1

9.9.9.9

Apply.

I had pretty much the same problem. For me, starting and stopping the firewall service cleared the fault. Restarting the router, reconnecting the ethernet etc had no impact. Everything was working on the ethernet port except DNS name resolution, which was stopping any internet traffic working correctly (unable to resolve names to IP addresses).

I had a similar issue. Try disabling and reenabeling the firewall service in settings. Cleared the issue for me.

I had this problem as well with my M1 Mac mini. Solution seemed to be turning the firewall service off then on again.

This actually worked for me. Don't know why, but starting then stopping the firewall was the key.

I have exactly the same problem. Nothing has helped so far :( This problem appeared when I updated to the Sonoma version of MacOS. Until then everything went and is going just fine (when I downgrade back). In between as I write this message it crashed 3 times... I have tried everything as you write but nothing has helped. If you manage to fix it, please let me know.

Sometime strange things happen on third party cheap router or older ISP routers, sometimes the firewall service stops1 If this firewall is three or more years old consider replacing it with something more modern! Once the firewall was issue that router could be on last year so consider getting newer one might be order if it is three or more years old!

Then that is still a bug 8) I’ve close the support case I had with Apple and updated them with my solution, but looks like the Ethernet port after upgrade is causing problems, there’s at least one other thread on here with the same issue.

Me too. Ethernet through thunderbolt dock. On one of them (Plugable), it works for 5-10 minutes and then dies. On the other (CalDigit TB3+), it drops for about a minute every half-hour. It makes time machine backups impossible, and remote work a bummer. Wi-Fi works without interruption. I've tried multiple cables, connecting directly to the router, even moving to an otherwise working ethernet setup at my wife's office. Works on her machine on Ventura, but not on mine with Sonoma.

Yeah, not sure what happened, but great to hear my friend! :)

Thanks.