Technical data
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Private and public addresses
There may be cases where you can not use or do not want to use public IP addresses
on your internal network, instead you can use private IP addresses (RFC1918). These
IP addresses will not work on an Internet connection, the solution is then to use NAT
(Network Address Translation).
Internal network
with private IP addresses
Router
with NAT
10.0.1.1 10.0.1.2 10.0.1.3
10.01.4 60.20.10.10
Internet
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
60.20.10.10 i.e. the IP address on the “outside”. In this way an internal IP address can
communicate with other computers on the Internet. It does not matter when another
internal IP address communicates at the same time as the router manages which ses-
sion belongs to which internal IP address and ensures the right traffic goes to the right
computer on the internal network.
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 - 192.168.255.255
B A C K