Cannot access server when another computer on the same network turns on a VPN

[itsbvb_check]

Hello,

Like the title says, I have a Jellyfin server running on a Windows 11 laptop (native; no Docker) on my home network. It typically runs just fine; I have a reverse proxy set up through Caddy and works when I am not on my home network, but on another laptop connected to my home network, I tried turning on a VPN (using Mullvad), and my server becomes inaccessible from outside of my network. It does however work on my home network when I try accessing through the IP address.

Are there specific settings I need to be utilizing within Mullvad or with any VPN that will stop this from happening?

Thanks in advance!

[TheDreadPirate]

Is this only affecting remote accessibility for the laptop? Or all clients?

[itsbvb_check]

Thanks for the response! It is only affecting remote accessibility; I tested it with my mobile connection just to be sure. I let the Jellyfin server run for a couple of days without turning on my other computer that has the VPN on it, and it worked just fine. But as soon as I activate the VPN on my other computer, I am not able to access the server via remote access. Let me know if I can provide anything that would help with this.

[TheDreadPirate]

I don't see how turning on a VPN on another computer would affect any computer other than itself.

Are you using a domain name or DDNS? Is the laptop running Mullvad also running the DDNS update client?

[itsbvb_check]

I completely agree, I am puzzled by it myself.

I am using No-IP Dynamic Update Client to check my IP on the Jellyfin server laptop and have a domain name set up through No-IP. I am currently not running anything like that on the Mullvad VPN laptop.

For a bit of backstory, I originally had Jellyfin running on Laptop A. I have since moved Jellyfin to Laptop B, and then on Laptop A, I removed Jellyfin, removed Caddy, and removed the No-IP Dynamic Update Client, and then installed Mullvad VPN.

Is it possible that my ISP is disabling remote connections to my server because of the VPN now? That is my only thought here. I have tried to do numerous things (adjust port forwarding, DNS flush), but no resolution. I am not sure if maybe I need to re-adjust my port forwarding perhaps?

And also for more context too, Jellyfin will still allow remote connections even if Laptop A is online, but only when the VPN is not activated. So I can still surf the web, etc. on Laptop A, and Jellyfin will still be operating correctly on Laptop B, but as soon as I activate the VPN on Laptop A, then Jellyfin will not work for remote connections (again, I checked this through my mobile connection to ensure I am not connected to the WiFi).

[itsbvb_check]

I should also mention too just for clarify that I have the same exact set up for Jellyfin on the new laptop. So I have it installed natively on Windows 11, using Caddy as the reverse proxy, and using the DUC from No-IP.

[TheDreadPirate]

Does your No-IP domain include an AAAA IPv6 record? And port forwarding on your router has been updated? Some routers have separate port forwarding tables for IPv4 and IPv6.

[itsbvb_check]

The problem is solved! I took the following steps in case anyone else comes across this:

Flush DNS from both laptops
Removed every single folder, registry, and network adapter related to VPNs
Re-logged into and reset the DUC from NO-IP (deleted and re-added the domain)
Logged in and out of the DUC on my desktop

Been about 3 hours since I did this, and my server is still accessible remotely. I will respond tomorrow if everything is still working as it should.