Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 5
Internet, Intranets, and Extranets

We all know what the Internet is—at least I hope so. An intranet is a TCP/IP based internet used for a business’ internal network. Intranets can communicate with each other via connections to the Internet, which provides the backbone communication; however, an intranet does not need an outside connection to the Internet in order to operate. It simply uses all the TCP/IP protocols and applications to give you a “private” internet.

When a business exposes part of its internal network to the outside community, it is known as an extranet. You may have used this extranet when browsing through a web page at General Electric or ordering some diskettes via a reseller’s Web page. You will not have complete access to a corporate network, but merely a part of it that the business wants you to have access to. The company can block access on its routers and put firewalls (a piece of software or hardware that allows you access to resources based on a variety of parameters such as IP addresses, port numbers, domain names, etc.) into place that force you to have access only to a subset of its intranet.