The meaning of the term SNAT varies by vendor. Many vendors have proprietary definitions for SNAT. A common expansion is source NAT, the counterpart of destination NAT (DNAT). Microsoft uses the acronym for Secure NAT, in regard to the ISA Server. For Cisco Systems, SNAT means stateful NAT. For Watchguard Systems, SNAT means static NAT.
Microsoft's Secure network address translation (SNAT) is part of Microsoft's Internet Security and Acceleration Server and is an extension to the NAT driver built into Microsoft Windows Server. It provides connection tracking and filtering for the additional network connections needed for the FTP, ICMP, H.323, and PPTP protocols as well as the ability to configure a transparent HTTP proxy.
Read more about this topic: Network Address Translation