Hi, have similar issues as many here, I looked at the post, but wasn’t able to solve the problem.
Core on iMac, 2019, 3.6/64RAM
Fiber Internet via “Glasfaser Stadtwerke Flensburg” - Wall mediaconverter “FiberTwist P2420” and router Fritzbox 7530. Core connected via ethernet
Thanks for taking the time to write in! As a next step, please connect your core directly to your main modem and see if you run into the same error message.
If so, there is a chance your ISP is running CG-Nat, in which you’ll need to reach out to them to request a static IP address.
I have no access to the fibernet wall box - after speaking with the provider, they say its not a router but just a “mediaconverter” with no remote access. They can’t offer me a static IP as a private person (only business customers), so as long as the setup of ARC is configured like this, I cannot use it.