Extranets can be also used to connect an intranet to Internet so that remote offsite access can be made in a company's intranet by an authorized individual. This can facilitate through an extranet.
Essentially, it uses smart cards and passwords to log in to a gateway server which checks requester's security credentials. If user checks out, she or he is allowed access into company's intranet structure.
A number of URL address are set aside for extranet and intranet use. Basically since intranets are self-contained networks, same set of addresses can be used by all intranets without conflict. Extranet addresses are designed such as to recognize intranets they connect and correctly preface every intranet address with an identifier. This enables two interconnected intranets to retain 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, because an intranet is a self-contained system, it just needs one class A network to designate main network. Sub networks use reserved class B and class C addresses. There are total of 16 class B addresses, from 172.16.0.0 to 172.31.255.255 and 256 class C addresses that range from 192.168.0.0 to 192.168.255.255.