I have an OpenVPN server running on my Synology NAS on local IP 192.168.9.36. I have an application on the NAS running on local IP 192.168.9.36:1234 and I have a reverse proxy that allows me to access my app over secure HTTPS (i.e. proxies https://myNAS.app to http://192.168.9.36:1234). I also have a DNS server on the NAS running on local IP 192.168.9.36 with a local DNS record that points myNAS.app to IP 192.168.9.36.
The problem resides when I am away from home and connect my mobile phone via an OpenVPN client to the OpenVPN server on the NAS to access my home network. In this situation I can access my app by its IP but NOT using its domain name (https://myNAS.app).
I believe OpenVPN is failing to push my local DNS server. In my VPN client configuration file (VPNConfig.ovpn) I have the following directives:
redirect-gateway def1 dhcp-option DNS 192.168.9.36 dhcp-option DNS 188.8.131.52
When connected to the VPN and querying my current DNS server, I am told that I am using Google (184.108.40.206) which should be the secondary and not primary DNS.
What am I doing wrong? Why is 192.168.9.36 not being pushed as my primary DNS to my mobile phone over the VPN connection?
Note: all addresses are fictional, not intended to be clicked.
From comment by OP
I am using an iPhone with iOS, cellular data when connecting to the VPN. VPN is running on Synology official VPN Server package but for DNS I'm using Pi-VPN running on the NAS in a docker container. If I remove the DNS entry for Google I am unable to reach any website by domain name, either local or public on the internet. (one note: in the OpenVPN config file it says I can have 2 entries, a primary and secondary).