I want to access the pihole admin interface over VPN (Fritzbox) by typing the local IP in the web browser(Firefox) of my phone.
Fritzbox 7530 is the DHCP server and the Raspberry is used as the DNS server
Actual Behaviour:
I only get a response if I type in the ip withput /admin.
On local devices in the network the admin interface works fine.
I can also access other devices in net network over VPN, only PiHole interface doesn't work. I can also see that the traffic of my phone gets displayed in the PiHole Query Log.
Already tried reconfiguration with out success.
Do you see the Pi-hole landing page when you enter it's LAN IP?
Is there any text or error shown when trying to access /admin, or an error in the browser console?
Did you try a different browser or a different device?
An idea I have is the CORS check that is implemented into the admin panel, although it shouldn't fail when accessing via VPN, but only when a proxy is involved which changes related request headers. You'd see a related error message.
If DNS resolution for pi.hole fails via VPN, but you can resolve local hostnames, your VPN client could be using your FritzBox as DNS server.
You should check your VPN software's DNS settings on your VPN client.
You also mention that you can observe your VPN phone client's DNS traffic in your Pi-hole's Query Log.
That may still happen when your VPN client is using FB for DNS, if you'd configured your FritzBox to use Pi-hole as its upstream DNS server (in addition to distributing it as local DNS server via DHCP).
If that's the case, you may have to exempt your Pi-hole's hostname (and possibly other local name definitions) from your FritzBox's DNS rebind protection.
Note that this should not be necessary if you manage to set your VPN clients to use Pi-hole for DNS directly.
Strange, as both is served with the same webserver. What do you mean by "no response"? What is the HTTP response code, or is it a connection timeout?
Which VPN server are you using currently and on which machine is it running? WireGuard then? If you want to access LAN hosts via their local hostnames, then I agree with Bucking_Horn that using the router (IP) as DNS in the VPN client configs and Pi-hole as upstream for the router should be the easiest setup.
If there is a general issue with LAN host connections via VPN (regardless if you use local hostname or IPs) then verify that IP forwarding is enabled on the VPN server system and allowed by iptables FORWARD chain in case.