Hi @meldano,
Please see the staff post here for more context and for a lost of known workarounds for Vodafone Germany users encountering their blanket residential IPv6.
Note that the Roon Labs team is actively researching additional methods of accessing ARC outside the home that will strike a balance between security, required infrastructure for both users and Roon, and the existing service provider landscape. We recognize that carrier-grade address translation in certain forms will require users to take extra steps to enable mobile playback. With certain carriers, ARC won’t function at all in its initial implementation. Vodafone Germany’s blanket IPv6 implementation and particular dual-stack lite is an example of one of these. It’s a frustrating situation and a compromise some users had to stoicly endure for the initial release, although our goal remains for ARC to be an out-of-the-box feature despite the wild diversity of networking conditions among our user base. We’ll get there; we’re just not there yet.
Please see the thread @Ian_MH linked above for the most up-to-date list of solutions and workarounds for circumnavigating the dual-stack lite implementation on Vodafone residential-tier accounts: Vodafone Germany w/ ISP-Supplied Modem/Router (Fritz!Box or Touchstone): 502/504 Errors - #56 by connor