The title of this sidebar may be a bit confusing and look a bit informal with the odd capitalization, but it’s for a very good reason. While internet is a truncated version of internetwork, a lot of play has come from the root of these words. Let’s examine the word internetwork first, just to make sure we understand where all the variants come from. As you know, a network is a conglomeration of devices tied together with a common technology. Well, once you establish two or more of these networks, work can be started on bringing them together. The interconnection and intercommunication between these autonomous networks is known as an internetwork or just internet. We know we have an internet when we use routers or other layer 3 devices to interconnect the networks. What kind of fun can we have with these words?
First of all, just by capitalizing the word internet to form Internet, we get the proper name of the global commercial internetwork that is tied together by TCP/IP (actually, all of these entities are) and that has a scope of the planet we call home. If those Mars rovers have IP addresses, the scope suddenly gets a bit grander. That’s the flexibility of TCP/IP for you. What if we analyze the meaning of inter? An internet is connectivity and communication across network boundaries. Does that mean, then, that an internet is connectivity and communication within a network? Gotcha. An intranet is more an opposite of the Internet, in terms of scope. If the Internet spans many administrative boundaries, encompassing many disparate networks, then and intranet, while often an internet (how’s that for a catch?), encompasses only networks under a single administrative domain, a large corporation’s internal internetwork. Did you catch that? An intranet can be an internet, but not the Internet. Fun, huh?
Well, the, that just leaves extranet. Think of an extranet as an intranet becoming a very controlled internet. That is, if an intranet is mode up of all networks under a single administrative control, then an extranet is the expansion of that to include one, two, or just a few a additional outside networks. Said differently, an extranet is an intranet interconnected and intercommunicating with networks that are under separate administrative control. This isn’t nearly as unruly as the Internet, because this interconnectivity arose from some sort of partnership or affiliation between the parties. Let’s say, for instance, that a manufacturing company wants to have vendor monitor its inventory so that whenever materials that the vendor supplies reach a minimum threshold, an order can be generated automatically, without personnel from the manufacturing company getting involved. That would require some sort of limited vendor access to internal manufacturing company resources’. While the manufacturing company resources. While the manufacturing company wants the vendor to have access to all that they need to help automate the supply process, they don’t want the vendor accessing sensitive financial, personnel, or possibly engineering information. By tweaking the firewalls just so, the vendor’s trusted network assets can be allowed access to the manufacturing company’s inventory control system but nothing else. That’s an extranet. While there’s a bit=g difference between them all, they are all very similar. They are all generally TCP/IP internetworks.