Network Address Translation is an Internet Engineering Task Force (IETF) standard used to allow multiple PCs or devices on a private network (using private address ranges such as 10.0.x.x, 192.168.x.x, 172.x.x.x) to share a single, globally routable IPv4 address. A main reason NAT is often deployed is because IPv4—the current generation of the Internet—addresses are getting scarce.
NAT is used in gateway devices that form the boundary between the public Internet and the private LAN. As IP packets from the private LAN traverse the gateway, NAT translates a private IP address and port number to a public IP address and port number, tracking those translations to keep individual sessions intact. Internet Connection Sharing in the Windows XP and Windows Me operating systems, along with many Internet gateway devices use NAT, particularly to connect to broadband networks such via DSL or cable modems. The use of NAT is increasing dramatically as more homes and small businesses network their PCs and share a connection to the Internet.
