The public IP addresses are assigned by the InterNIC and they are guaranteed as unique addresses. It is therefore possible to obtain the IP addresses for the Intranet computers, normally directly by the Internet Service Provider to which we are connected, and use these addresses with no problems of conflicts with other Internet hosts. In this case the router has to be programmed to allow the circulation inside the Intranet of the packets with IP addresses of the Intranet itself, and to send towards the connection to Internet the packets with different IP packets. The high number of carried out Intranet has led to the requirement of a very high number of IP addresses, by saturating the availability of the same, so we can't think that each host of an Intranet has a unique IP address for the whole Internet. Besides, normally, inside an Intranet, not all the computers need to connect directly to Internet. As a matter of fact we can structure the Intranet with the presence of a proxy server carrying out the interface tasks towards Internet for all the Intranet hosts. Each time that a host needs to open a Web page from a remote site, sends this requirement to the proxy server, that later mails it to the remote server.