There may be cases where you cannot use or do not want to use public IP addresses on your internal network, instead you can use private IP addresses. These IP addresses will not work on an Internet connection, the solution is then to use NAT (Network Address Translation).
A router or “firewall” with support for NAT translates private addresses to public addresses:
When the computer with address 10.0.1.2 needs to access the Internet, 10.0.1.4 is addressed which is the “Default Gateway” or “way out”. When data from address 10.0.1.2 passes through the router NAT translates the internal IP address 10.0.1.2 to 220.127.116.11 i.e. the IP address on the “outside”. In this way an internal IP address can communicate with other computers on the Internet.
IANA (Internet Assigned Numbers Authority) has reserved the following three address blocks for IP addresses in private networks:
10.0.0.0 - 10.255.255.255 172.16.0.0 -
172.31.255.255 192.168.0.0 -