I am posting this on Ubuntu, since Linux Mint is quite related to it and I think this behaviour is the same on both.
I am using the Networkmanager GUI in Cinnamon.
My Linux Mint box connects to WLAN hotspot, which acts as DHCP server and propagates itself as DNS server. So far, so good.
However, when I connect to a VPN, the DHCP server of the VPN tunnel assignes an IP address to my client (which works) and a DNS server - which is ignored. Even entering the DNS server statically is ignored.
How can I tell Networkmanager/DNSMasq to use another DNS server when connected to the VPN? I cannot find anything related on the GUI, neither in the docs how to configure it in a config file.
Note, this DNS server must only be used in the VPN, because it is a company-wide DNS server which resolves a local TLD (.loc). It is not done by replacing the standard DNS server (the WLAN hotspot) with a public one.