To solve the problem of the limited number of IP addresses, and of the absolute oneness of the same, the private IP addresses have been introduced. Some IP addresses portions have been destined to be used as private addresses inside the Intranet, by assuring that they aren't part of the public ones and so by avoiding an address duplication. The private addresses are defined in the RFC 1918 and they are divided in the 3 following blocks: 10.0.0.0 ÷ 10.255.255.254 allow to carry out a class A private network and relative subnets by using 24 bit to locate the network hosts 172.16.0.0 ÷ 172.31.255.254 allow to carry out a private network with 20 bits to locate the hosts, or 16 class B networks. 192.168.0.0 ÷ 192.168.255.254 allow to carry out a private network with 16 bits to locate the hosts or 256 class C networks. The private addresses can be duplicated in any number of Intranet. There are no problems of conflicts because there aren't paths in the Internet routers leading to these addresses. The private addresses can't be reached in Internet