Research DYNDNS to see if that can be used.
I'm using FireZilla Server behind an NAT router on port 21. As I intend to use this remotely, I need my router to ensure that the port points to my computer at all times (or at least when it's connected).
I can do a manual port forwarding, but there isn't a feature for static DHCP on the router, and I cannot use static IP configuration on my computer because I also intend to carry it around with me.
I can forward a different port to a different IP address and make FireZilla bind to each of these IP addresses (one will be correct), but this would be extremely infeasible and insecure.
I can periodically map port 21 to my computer using a program on the computer itself, but the few programs I have found which maps uPnP ports do not do it automatically (detects when you reconnect to a router) or periodically (say, every 10 minutes).