Greetings, Bennet. This is so long ago that I don’t even have an RV016 any longer. But here is my stab at your question. If your ISP only issues you a single IP address, then you can only use traditional NATing i.e.: one external (WAN; the IP provided by your ISP) to multiple internal (LAN: the IP addresses on your home network. In this configuration, an inbound request from the Internet on a particular port such as HTTP can be directed to a single address on your LAN via port mapping.

However, what do you do if you have multiple machines on your LAN that you want to respond to that port (e.g.: multiple HTTP servers on port 80)? That’s where one to one NAT would come in. Your ISP would have to provide you with multiple IP addresses assigned to your single MAC; the router would detect each IP address and direct it to a different LAN IP, so you could have multiple HTTP servers (for example), each responding to a different inbound IP address.

As I recall, the RV016 can perform either function: traditional, or one to one. Obviously, if your ISP only gives you the single IP address, you only have one choice.