Multiple NAT means that there are two ‘routers’. This could be because you have two routers on your local network (e.g. an ISP supplied modem/router and one that you have added - possibly as part of a mesh WiFi system) or if could be your router and a gateway (a powerful router) used by the ISP as part their CG-NAT solution.
The diagnostic text gives the external (WAN side) ip address of the router to which your Roon Server is connected. This ip address is:
In a different subnet to your Roon Server (as you would hope)
In a non-routable ip address range reserved for local networks which should not be issued by an ISP.
Whilst not eliminating the possibility of the ISP using CG-NAT (and thus a gateway/router), it does strongly indicate that you have two routers in your local network.
As a first step, you should address this issue. I recently posted guidance to someone else with the same issue. You may be able to use the information in that post to help you.
If you either eliminate the double router issue or set up double port forwarding match and you still have ARC connectivity issues, then the ISP may be using CG-NAT as well.
Alternatively, you can just go the Tailscale router and ignore port forwarding completely - including all of the status issues you have quoted above.
Great to see you on the community again! @Wade_Oram is spot on with the above response, let us know if you’re able to give it a read, and let us know your results!
