Simply add a Port Forwarding on your router.
A few links to get you started:
http://en.wikipedia.org/wiki/Port_forwarding
http://en.wikipedia.org/wiki/NAT
And probably this one:
http://en.wikipedia.org/wiki/UPNP
Example:
- Your router (public IP) receives a connection on port 80 (or any other port you configured)
- Your router knows, that all requests on port 80 should be forwarded to a specific computer in your network (depending on your router you might have the option to choose from either MAC-Adress, static IP or computer Name)
- Your router will forward that connection request to the pc you configured.
This setting is usually accessible via the web-interface of your router
To configure it you have to know a few things beforehand:
- Internal IP of your server (100.10.10.12)
- Protocol (UDP and/or TCP)
- Port or Portrange (80, 443, 8001-8009, etc.)
Important!
You will (most certainly) not be able to test that connection from within you network.
To test it from outside you can use this site for example:
http://ping.eu/port-chk/
It will try to connect to a specified port and tell you if it was able to establish a connection.