|NAT||NAT (Network Address Translation) is an IETF standard that enables LANs to use one set of private IP addresses for internal traffic an another set of IPs for external traffic. Typically, a NAT device makes all IP address translations where the LAN meets the WAN.
NAT permits a large number of LAN users to share one external IP address, and adds some network security, since private IP address ranges are not routable outside the LAN.
The following 3 blocks of the IP address space have been reserved by the Internet Assigned Numbers Authority (IANA) for private Intranets:
10.0.0.0 - 10.255.255.255 (class A, 10/8 prefix)
172.16.0.0 - 172.31.255.255 (class B range, 172.16/12 prefix)
192.168.0.0 - 192.168.255.255 (class C range, 192.168/16 prefix)
Resources: NAT-RFC1631, Private IPs - RFC1918