Originally Posted by Kustom42
How is that possible if the IP is dynamic and changing? I disagree with this but I have been wrong before. If you can give some resources to explain this it would be appreciated as it goes against everything I know and have been taught.
The changing IP makes no difference. Incoming connections are directed to the router itself, the router has the public IP. It's then up to the router to decide what to do with the incoming connections. The most common scenario is to use port forwarding to selectively send incoming connections to various local machines based on the port, or filter them out with the firewall.
The only effect that a dynamic IP has is that you need to remember to connect to a different IP whenever it changes, and you might need to reboot the router whenever the IP changes on the modem (most ISPs in my experience only change the IP after you cycle power, which probably will only happen after a power outage, in which case the router is being power cycled anyway).
My home setup has a single dynamic IP with port forwarding set up. Incoming connections on port 45631, 3389, and 14081 are directed to one machine (air video server, remote desktop, and torrent), incoming connections on port 21, 22, and 80 are directed to a different machine (ssh, ftp, http), and incoming connections on another port are directed to a networked webcam.
The individual machines need to have static IPs on the local network, but the changing public IP isn't a problem.