The Internet is a global interconnection of computers and servers around the world; it covers everything. An intranet is a smaller interconnection of computers and servers within a defined area, such as a company's secured website. An extranet would be an interconnection of computers and servers that are outside the intranet.
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Similarities
In the current times, intranet can be considered more of a business tool which keeps an organization connected in a structured manner. It is, however, to be always remembered that intranet is a part of internet. Thereby, intranet does share some very basic features with the internet. Some of them are listed as under:
Intranet uses the internet protocols including TCP/IP and FTP.
Though the access is limited, intranet can work on any of the web browsers. Some organizations do have a customized web browsing environment as per their requirement.
Organizations that have intranet services often have their own instant messengers or communicators. These can be compared to Yahoo Messenger or Gtalk applications.
Security features like firewall and encryption-decryption policies are applied using same or similar features that internet has. A number of organizations have different encryption techniques so that any undesirable breach of data is not possible because of patterned studies.
Difference:
Internet
Internet is wide network of computers and is open for all.
Internet itself contains a large number of intranets.
The number of users who use internet is Unlimited.
The Visitors traffic is unlimited.
Internet contains different source of information and is available for all.
Intranet
Intranet is also a network of computers designed for a specific group of users.
Intranet can be accessed from Internet but with restrictions.
The number of users is limited.
The traffic allowed is also limited.
Intranet contains only specific group information.