Reference Manual

The NAT32 Interface Selection dialog box lists all Network adapters known to Windows. When an adapter has an X in front of its name, NAT32 has detected a problem with it and displays a red warning message in the Adapter Details field. Such adapters should normally not be selected for use by NAT32.
 

The sample at left shows a system with two LAN adapters and several NdisWan adapters, one of which is used for incoming RAS Connections. The second Realtek adapter has been selected as the Private LAN adapter and one of the other adapters should be selected as the Internet adapter. To facilitate the selection of NdisWan adapters, the desired RAS Connection(s) should be dialed before configuring NAT32. Each connected NdisWan adapter will then have an IP address and a Connection Name, which will be displayed in the dialog box.

Further details can be found in the NAT32 Help files.