NOTE: This only applies to OpenVPN version 2.39 and higher.
From the GUI in the lower right task bar right click.
Pick the connection you want to use and right click on it.
Select Edit Config
After the lines that start with the word “remote” create a blank line.
In that blank line paste
block-outside-dns
Save and exit.
Do this for all the other connection you use.
OpenVPN will now prevent outside DNS from being used.
EXAMPLE:
Original config (top of file)
client
dev tun
proto udp
remote exampleserver1.server.com
remote exampleserver1.server.com
mssfix 1300
resolv-retry 60
nobind
auth-user-pass
Modified config (top of file)
client
dev tun
proto udp
remote exampleserver1.server.com
remote exampleserver1.server.com
block-outside-dns
mssfix 1300
resolv-retry 60
nobind
auth-user-pass