I've got a NAS that serves multiple services through multiple ports. System administration goes through 8080, bittorrent goes through port 9000, etc. When I'm a t home, I'd type the server's IP and the port to access it, like 10.x.x.x:8080. When I'm away, provided that I forward those ports to the server's IP in the router, I can access the stuff through 123.x.x.x:8080, or 123.x.x.x:9000. If I set up a domain name, I can go mydomain.com:8080, mydomain.com:9000. That's really useful.
Now suppose that where I am (work, of course), everything is blocked but http. This means that if I wan to access the system administration portion of the NAS, I have to forward http communication from 80 to 8080 into the NAS's IP. That limits my access to one service only. I would like to access them all, but I don't have multiple IP addresses (actually, I barely have one, I use dyndns to track my dinamic IP).
I'm guessing you know where I'm trying to get. I would like to be able to set subdomains like admin.mydomain.com, www.mydomain.com, torrent.mydomain.com and have them all coming through the http port. I believe what I'm looking for is a proxy, or a reverse proxy, I don't know yet, cause I'm not very savvy in this sort of thing. Dyndns does no allow me to set subdomains and even if it did, I could not specify ports for it, only IP addresses. The solution must then be internal, but I don't see my NAS offering any sort of "internal DNS" or internal proxy server.
It does have a virtual host option with the webserver, and I've seen in this post http://serverfault.com/questions/140125/port-to-subdomain a solution that seems to be what I'm looking for, but I'm not sure.