Static NAT

Registered addresses are necessary for advertised kinds of resources, such as publicly accessible servers on your network, because these machines must be at well-known, fixed addresses. Static NAT is frequently used to provide public access to HTTP or FTP servers that use private addresses. These servers must use static NAT reverse rules so that other hosts can use the same registered addresses to reach them, so the reverse rules must be generated by you.

Static NAT maps a specific unregistered address to a specific registered address. Static translations can also map a range of unregistered addresses to a range of registered addresses, which requires the number of addresses in each range to match.