Private IP Subnets

link: http://networking.ringofsaturn.com/IP/subnets.php

Private IP Addresses
RFC 1918 requests that organizations make use of the private Internet address space for hosts that require IP connectivity within their enterprise network, but do not require external connections to the global Internet. For this purpose, the IANA has reserved the following three address blocks for private internets:
10.0.0.0/8
127.0.0.0/8
172.16.0.0/12
192.168.0.0/16
IP's above 224.0.0.0 are used for both multicast and experimental purposes.