My previous DSL modem had a function called "DMZ Host" (which in other platforms seems to be named Default Host). When you select a computer in your network to be the DMZ Host, it forwards every non-manually forwarded port to that computer as well as assign via DHCP the modem's external IP to that computer (dmz host).
So, effectively, it is duplicating the external IP and giving it to the internal computer. For a variety of reasons, this was handy, particularly for picky programs (random ports) or gaming.
But now that I've changed to optic fiber, the modem does not have that functionality. I am planning to create a Linux-box for routing purposes. Is there any way to recreate the same functionality with iptables?
Hints involving other platforms/software are very welcome.
I'm attaching a diagram for better clarity (an edit of the picture from this question: Accessing the DNAT'ted webserver from inside the LAN ) in here:
Thanks a lot in advance! I've been trying to find information about setting this up but I've been unable to. Maybe i'm using the wrong search terms.