Roon ARC strange behavior

[Axel_Lesch]

I’m afraid you can only figure it out systematically and with a lot of patience.

Again I had a look at AVM’s Knowledge-base, “Checking accessibility of the FRITZ!Box in the internet”, giving the information that:

Mobile network providers usually block incoming connections

Checking accessibility of the FRITZ!Box in the internet | FRITZ!Box 6850 5G

As far as my own system with a German Telekom SIM card is concerned, this never was the case.
However, I remember another case where it was exactly like this.

I can't get ARC to work

I had a thing initially where the Roon ARC settings also said Ready (and I had a proper IPv4) but it didn’t work with the Vodafone home internet from my phone because all ports were blocked when accessed from the outside through the Vodafone cell network. It worked when the phone was in the Telekom cell network. This was caused by a misconfiguration either in the Vodafone cell network or in Vodafone’s cheap router that I was using at the time. It went away as soon as I switched to a private Fri…