External DNS to Internal lan servers

I’m running IPFire core update 153
I have Nginx Proxy Manager set up at my lan to acces lan webservers.
When i resolve an external domaine name at cloudflare ex. test.domaine.com pointing at my router IP (IPFire), forwarded to Nginx Proxy Manager, I get the corresponding webserver.
That is actually what I want, but that did’nt work when I was running DD-WRT. Then I had to set up a split dns, for my internal lan network.
How is that posible?