IPv4 - NAT - Interface - Properties Page - NAT Tab

Private interface connected to private network

Specifies that this interface is a private interface that is connected to the private network. The NAT protocol translates IP packets sent from this network to the public network by mapping them to the single public IP address and an arbitrary port number. The RRAS server maintains a table with these mappings so that the reply from the server on the public network can be forwarded back to the originating host on the private network.

Public interface connected to the Internet

Specifies that this interface is the public interface that is connected to the Internet.

Enable NAT on this interface

Specifies whether the router performs TCP port and UDP port translation in addition to IP address translation. If you only have a single public IP address, you must select this check box. Otherwise, network traffic from hosts on the private network cannot be properly translated to Internet traffic. This check box is enabled only when you select Public interface connected to the Internet.