Could be an ISP issue with your external IP address. ISP networks often don’t provide real IPv4 addresses that can be port forwarded, but instead use something called CG-NAT (Carrier-Grade Network Address Translation).
In that case, enabling a VPN may work around it like @Saravanan_Kannan wrote
Alternatively, sometimes the ISP can accommodate you. Let me copy the usual response by Roon support for this issue:
If you only have one router in your setup or your modem is already in Bridge mode, please take a look through our list of known router and internet service provider solutions, as other users may have already encountered the same situation: ISPs and Routers: List of Known Solutions and Workarounds
You can reach out directly to your service provider to ask if they support port forwarding; this question will often enough to prompt them to explain whether or not the carrier-grade NAT they’ve implemented can function with ARC.
More specifically, you can pass along the following questions:
- Have you implemented carrier-grade NAT for my account level?
- Have you fully implemented IPv6, or do you have IPv4 addresses available?
- Can I request a static IPv4 address to support port forwarding?
- Are there any ports you have reserved at the ISP level I should be aware of?
If you’re unable to locate an existing solution in our #support:port-forwarding-resources subcategory, please reach out to the Roon support team and include the following information:
- What is the make and model of your modem and router?
- Do you have any additional network hardware, like additional routers or managed switches?
- Who is your internet service provider and what is your geographic region?
- Is your Modem configured in Bridge Mode so that it operates only as a modem or do you have the ports forwarded on both?