Trying to understand...
If L2TP is used to connect via a tunnel to your ISP, how will it use your ISP for its DNS look up, that is to travel through the tunnel that is not open yet?
I can understand when the base is say DHCP that then returns the IP for DNS. Then DNS looks up target server, that returns L2TP server address, then open the tunnel.
Again sorry for confusion. This setup is something that is not used in my immedate area.