Public or private network?

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 needs to access the Internet, is addressed which is the “Default Gateway” or “way out”. When data from address passes through the router NAT translates the internal IP address to 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: - - - 

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