RFC 1597 provides for a group of Internet Networks that will never be assigned. The private addresses will also not be routable through the Internet, preventing communication with networks on other subnets. The implementation of the Private IP address scope makes it the proper choice for use on company Intranets and for home/SOHO networks. These IP addresses have been specifically selected to use when it isn’t necessary or desired for computers on the Internet to connect to IPv4 based deviced on your network.
With use of a proxy server, firewall, or router, users and devices with non-routable IP addresses are allowed to access the Internet through a single IP address provided by their service provider. The devices achieve this through the process of Network Address Translation (NAT), allowing the nonroutable addresses to communicate with Internet-based, routable, Public IP addresses.
Reserved IP addresses for Private Networks are the following:
10.0.0.0 – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255
A complete and current list of all IP Address Allocations can be found at the Internet Assigned Numbers Authority’s (IANA) website: http://www.iana.org/numbers/