Key difference: The Internet is the massive global system that connects computer networks around the world together. Millions of private, public, academic, business, and government networks worldwide connect with each other over the internet to share massive amounts of information, resources and services. Intranet is an internal network. It is used by companies to connect their computers on a network. Only the members of the corporation with authorized access may log on and access the network and the data on the network. Extranet, on the other hand, is an internal network that can be accessed externally. The extranet can be thought as an extension of the company’s intranet. People from outside the company can have a limited access to the company’s internal network for business or education related purposes.

The Internet is the massive global system that connects computer networks around the world together. Millions of private, public, academic, business, and government networks worldwide connect with each other over the internet to share massive amounts of information, resources and services. Internet is what we use to access web pages, send e-mails, listen to music or watch videos online. It hosts an extensive range of information, one that we generally take for granted today.

The Internet uses the standard Internet protocol suite (TCP/IP) to allow us to connect to the net. It has numerous information resources and services, such as the web pages of the World Wide Web (WWW), games, videos, images, e-mail, social networking, etc. It has even spawned new services such as Voice over Internet Protocol (VoIP) and Internet Protocol Television (IPTV). The Internet is currently being used by billions of people worldwide.

The Internet carries information from all streams; traditional, such as newspaper, book and other print publishing; and modern such as blogging and web feeds. It also enabled new forms of human interactions through, instant messaging, e-mail, Internet forums, and social networking. It has gained so much popularity that in fact almost all forms of business communication as well as personal happens online through e-mail, instant messaging and social networking. With phone calls and text messaging (SMS) coming is second.

Intranet, on the other hand, is an internal network. It is used by companies to connect their computers on a network. Webopedia defines intranet as “a network based on TCP/IP protocols (an internet) belonging to an organization, usually a corporation, accessible only by the organization's members, employees, or others with authorization. An intranet's Web sites look and act just like any other Web sites, but the firewall surrounding an intranet fends off unauthorized access.”

The intranet is based on TCP/IP protocols, however, it is inaccessible from the outside. Only the members of the corporation with authorized access may log on and access the network and the data on the network. Like all networks, the Intranet is mainly used to share data, information, resources, company programs, software applications, as well as facilitate communication between people or work groups within the company. Intranet improves the data sharing capability and overall knowledge base of the company’s employees.

While, anyone can setup an intranet; it is mainly used by corporations as it is a secure network and is much less expensive to build and manage than private networks based on proprietary protocols. In fact, Intranets are considered to be one of the fastest-growing segments of the Internet.

Extranet is basically an internal network that can be accessed externally. The extranet can be thought as an extension of the company’s intranet. People from outside the company can have a limited access to the company’s internal network for business or education related purposes. The access may be granted to the organization’s partners, vendors, suppliers, current and potential customers, etc.

Webopedia defines extranet as “a buzzword that refers to an intranet that is partially accessible to authorized outsiders. Whereas an intranet resides behind a firewall and is accessible only to people who are members of the same company or organization, an extranet provides various levels of accessibility to outsiders. You can access an extranet only if you have a valid username and password, and your identity determines which parts of the extranet you can view.”

Webopedia also states that the extranets are becoming a very popular means for business partners to exchange information. However, the extranets require security and privacy, so that the information on the network is not wrongly accessed or misused by external parties. In order to protect the network, the extranets can incorporate firewall server management, the issuance and use of digital certificates or similar means of user authentication, encryption of messages, and the use of virtual private networks (VPNs) that tunnel through the public network.

SearchEnterpriseWAN lists some of the uses of the extranet:

• Exchange large volumes of data using Electronic Data Interchange (EDI)
• Share product catalogs exclusively with wholesalers or those "in the trade"
• Collaborate with other companies on joint development efforts
• Jointly develop and use training programs with other companies
• Provide or access services provided by one company to a group of other companies, such as an online banking application managed by one company on behalf of affiliated banks
• Share news of common interest exclusively with partner companies

The main difference between the Internet, an intranet and the extranet is that the Internet is open to all, whereas the intranet is a limited network and is only open to those with appropriate access. Intranet is the network that is limited for use on the organizations computers, whereas the extranet is an extension of the company’s intranet. The extranet makes available some of the information of the intranet to people not directly connected to the intranet. The Internet is open to all and everyone has equal and complete access to it. Whereas, the intranet can be accesses by the organization’s staff and the extranet provides limited access and to a limited group of people outside of the organization.

Image Courtesy: internet-turbo.com, milestonetechnocrat.com, etutorials.org