I presume by 'internal ip' you mean a masqueraded, private IP (such as 192.168.0.0/16 or 10.0.0.0/24) The easiest way to do this would via a split DNS - you have SOA records both inside and outside pointing to different IP addresses.

How to find your Router’s internal IP Address - wintips May 31, 2014 terminology - Are the terms "external IP address" and Yes, external and public IP address would be the same thing, and internal or private IP adress is the one you have inside your firewall/router. So for example, if you have a BT homehub, it will give your machine an IP address like 192.168.1.65.

Use NAT for Public Access to Servers with Private IP

Static route from external IP to internal IP Solutions

Hey , the ip assigned to me is 123.*.*.* , which isn’t a private ip , but when i visit sites to know my external ip , i get a different ip altogether. it is clear that the ip I’m getting is my external ip, visible outside my network. but how can i have such an internal or private ip .please explain!!

Apr 11, 2020 DNS resolution Windows Internal DNS to an External hostname/IP