Hi everyone,
My apologies for the delay in providing an official staff response to this question.
Depending on the implementation of carrier-grade network address translation, port forwarding might still work. Some networks have implemented a low-volume dynamic IPv4 address-sharing system in which ARC functions perfectly, provided that there aren’t local network issues disrupting the updated routable IP address from being communicated properly to the Core.
This unfortunately doesn’t appear to be the case with your provider, @Tekl, as you’ve already discovered 21 days ago (again, our apologies for the delay).
Many major providers in Germany have blanket IPv6 at this point for their residential-tier. While some longtime users with certain have grandfathered in their old static IPv4 external IP address, the general shortage of available IPv4 addresses has prohibited many users from even paying extra for a routable IPv4 address.
Vodafone Germany, for instance, has implemented an otherwise incredibly helpful form of dual-stack lite (DS-Lite); in their implementation, a local server can tunnel through the carrier-grade NAT, so to speak, provided that server has a static local IPv6 format address. Roon Cores don’t support IPv6 addresses at this time.
From what I can tell reading around and as you’ve already reported, 1&1 shares a similar dual stack implementation.
Here’s where Roon stands:
We’re fully aware that port forwarding is an increasingly outdated method for enabling mobile playback via a 4G or 5G device, and we recognize that a broad number of our users will ultimately hit a hard wall with the particulars of their ISP’s carrier-grade NAT, 5G routers, etc.
We’re actively researching alternative (and more up-to-date) solutions for mobile playback that will democratize access to ARC. We’re also working separately to allow for Cores to support IPv6 addresses, which would provide a solution to many users with the dual-stack implementation in your example case. I don’t have a timeline for either initiative, but rest assured we’ll be posting as soon as we do. I recommend you keep an eye on this thread in the meantime for more context, given the similarities to your situation:
There are several solutions broadly reported by Vodafone.de users we’ve aggregated in that thread that may apply to 1&1, as well.
We’ll be watching for your response, and we’ll be here to support as necessary. Thank you again for your patience.