Intranets are basically 'small' Internets. They use the same network facilities that the Internet does, but access is restricted to a limited sphere. For instance, a company can set up an intranet within the confines of the company itself. Access can be tightly controlled and limited to authorized employees and staff. There is no connection to the Internet or any other outside network. Functions like web sites, file uploads and downloads, and e-mail is available on intranets within the confines of the network. Since frivolous sites are no longer available, there is no employee time lost due to accessing them. There is, of course, the limitation of the networking area. The very benefit of restricting access to all of the facilities available on the Internet also restricts communication to other desirable locations. This is where the extranet steps in.


An Extranet is network that connects a number of intranets into a truly mini-Internet Access is extended to all the intranets connected through the extranet, but, again, not to the Internet.  Extranets requires a constant Internet connection and a hypertext transfer protocol (http) server. Extranets can also be used to connect an intranet to the Internet so that remote offsite access can be made into a company’s intranet by an authorized individual. This can facilitate through an extranet.

Basically, it uses passwords and smart cards to log in to a gateway server that checks the requester’s security credentials. If the user checks out, he or she is allowed access into the company’s intranet structure.

A number of URL address are set aside for intranet and extranet use. Essentially because intranets are self-contained networks, the same set of addresses can be used by all intranets without conflict. Extranet addresses are designed to recognize the intranets they connect and correctly preface each intranet address with an identifier. This allows two interconnected intranets to retain the same set of address values and keep them from being mistaken. One class A address, ranging from 10.0.0.0 to 10.255.255.255 is reserved for intranet usage. Again, since an intranet is a self-contained system, it only needs one class A network to designate the main network. Sub networks use reserved class B and class C addresses. There are 16 class B addresses, from 172.16.0.0 ti 172.31.255.255 and 256 class C addresses, which range from 192.168.0.0 to 192.168.255.255.