If you can’t Bridge the ISP modem/router combo, then you have two active NAT layers in your network. There might be an additional layer of NAT put in place by your provider, called CG-NAT (this is the only reason you’d need a static/dedicated IP).
Here are your options:
Try connecting RoonServer via ethernet to the ISP modem/router instead of the TP-Link. The, try to autoconfigure ARC via UPnP.
Enter the web GUI for both the TP-LINK and your ISP router and create an identical port forwarding rule in both. This should be a TCP-format rule pointing to the RoonServer IP Address and Port Number listed in Roon Settings → ARC.
If you are still receiving a multipleNAT diagnostic in Settings → ARC with either of the above setups, then your ISP likely has CG-NAT and your only options will be to request a dedicated/static IP address or to bypass port forwarding using a VPN or alternative unsupported method in Tinkering.
I called my ISP and they DO NOT offer static IP addresses for the moment. I’m still getting the “multipleNAT” diagnostic in Settings. So, I don’t know what I can do.
I’m loving Roon and I really want to make it work before my Trial period expires, but ARC is essential to me, I need to find a way to make it work.
Is there any way we can connect in a zoom/teams call so I can show you my screen and we can try to fix it together live?
If your ISP doesn’t offer a way to bypass their CG-NAT, you can also inquire if they have native IPv6 available.
Unfortunately, there’s no setting within Roon that can bypass an implementation put in place by your internet provider. You’ll have to explore an alternative solution like TailScale or another consumer VPN in Tinkering. These unofficial methods to bypass the multipleNAT put in place by your ISP are well-documented by other users, but they’re not officially sanctioned in the Support section.
Please reach out if you need a trial extension to continue troubleshooting - we will happily sync with our accounts team to add more time so you can try ARC.