> well, as long as there is a single machine that wants to listen on that port, at least Well yes, most networks have more than one machine and multiple users

> well, as long as there is a single machine that wants to listen on that port, at least Well yes, most networks have more than one machine and multiple users might want to run the same service. > you'll also need some kind of network address translation at the edge. Not at all, each machine gets two addresses - one routable from the ISP and one non-routable from the router. Internal services simply use the non-routable ones.