An extranet is an intranet with a twist. An intranet is an online network belonging to an organization, usually a corporation, which is accessible only to the organization's members, employees and other authorized users. Intranet Websites look and act just like other Websites but include a firewall that prevents unauthorized access. Intranets are used to share information within the company. Secure intranets are now the fastest-growing segment of the Internet because they are much less expensive to build and manage than private networks, which require expensive cabling and dedicated connections.
Intranets use the Internet as their connection medium.
An extranet is an intranet that allows various levels of accessibility to authorized users. Your valid username and password determine which parts of the site you can view. Extranets are becoming a very popular means for business partners to exchange information. Setting up an internal corporate intranet is a relatively easy task for a qualified networking consultant but until recently, allowing access beyond the office walls involved expensive, high-speed digital connections. IIS is a free add-on to Windows NT Server.