Intranet
Internet is something that is wide spread and but what if it contracts and has information only about you and your firm and is accessible to only authorized members of your organization this is where an intranet comes into existence. An Intranet looks and acts like a website but the difference arise at point that there exists a firewall that fends off unauthorized access. Their main use arises for sharing of information and is much less expensive to build and manage than private networks based on proprietary protocols.

Advantages of Intranet
Ease of Publication: Intranet is very useful for publishing information in the organization internally.
Cost: In comparison to other Software packages Intranet is not expensive.
Usability: Many users already have Web Browsers and have the ability to access the internal web sites easily.
Maintainability: The maintenance factor in intranet plays a very important role as all the data is placed right there at one place and it does not create a hassle to update the existing information or to add new.

Extranet
Intranet is useful only for the members of one single organizations but if the reach of intranet extends to members outside then that refers to extranet. But ‘outside’ we mean an extranet provides various levels of accessibility to outsiders (suppliers, vendors, partners, customers). An extranet is accessible only if the user has a valid username and password. His identity determines which parts of the extranet he can view. Extranets can be viewed as a very popular means for business partners to exchange information.