OS X Server: About the NAT Service
Summary
The NAT service is included in OS X Server (Mountain Lion), but it is not managed by Server app.
Products Affected
OS X Server (Mountain Lion)
The NAT service was provided by the natpmpd binary in Lion Server and the natd binary in Mac OS X Server v10.6. In Mountain Lion, natd is deprecated and natpmpd is used by Internet Sharing in the Sharing pane of System Preferences.
You can enable Internet Sharing to provide NAT services using the default IP address range of 192.168.2.2 to 192.168.2.254. Important: Do not enable Internet Sharing if you have configured custom settings for the DHCP service in OS X Server.