Private IP addresses and NAT
One of the early attempts of handling the exhaustion of IP addresses was the implementation of private IP addresses. Private IP addresses are not globally assigned, which means that different organizations may use the same private IP addresses. Private IP addresses are not routable, and therefore they are not accessible across the Internet. Organizations using private IP address internally for network connectivity use a process called network address translation (NAT) gateway or a proxy server to provide connectivity to the Internet. Each IP address class has a range of IP addresses that are reserved as private addresses. Table 19-2 lists the ranges for private IP addresses.
Private IP address range
10.0.0.0 to 10.255.255.255
172.16.0.0 to 172.31.255.255
192.168.0.0. to 192.168.255.255