Types of Networks

The Internet is a constantly growing network of computer networks based on the TCP/IP protocol. A protocol is an agreement on a method of communication. Just like Morse code is a convention in which a series of long and short signals represent letters of the alphabet, TCP/IP is a standard for structuring electronic impulses so that both the sending and receiving computers interpret the signals in the same manner and can thus pass information between themselves.

Originally what is now known as the Internet was a U.S. government project. Today it is a loose affiliation of large commercial electronic communications companies that have agreed to connect to each other so that the respective customers of each company can communicate with customers of all the other companies.

An intranet is a computer network normally belonging to one organization that uses TCP/IP. The technology is the same as the Internet; it's just restricted to a much smaller group of computers. An intranet could be a standalone network that is physically isolated from the Internet and thus unable to communicate with any computers on the Internet. Such an arrangement would be highly secure but of limited value in today's electronically connected world.

Typically an intranet is connected to the Internet at one or more points. Usually this connection is through a security device called a firewall. A firewall controls the kind of information and the target destinations to and from which information is allowed to pass. The most common purpose of a firewall is to let employees reach the sites and information that they need on the Internet while preventing outsiders from using the Internet to access internal computers.

A firewall may also block employees from reaching non work related sites on the Internet. It might also allow the public or selected remote sites to access web servers or other computers the organization wants to make available. Often a firewall is a general purpose computer running firewall software but a firewall may be a specially built single purpose computer. A firewall may also be a combination of routers and computers that perform the functions just described.

A LAN or Local Area Network is a computer network that is restricted to a small physical area. A LAN might use a different protocol such as Novell's IPX for the computers on the LAN to talk amongst themselves. A LAN can also use TCP/IP as its protocol. In this case the difference between a LAN and an intranet is that the LAN does not implement important features that TCP/IP can support. Specifically a LAN is not normally considered an intranet unless it has one or more web servers for internal only use on the LAN.

Many small LANs are still not connected to the Internet but increasingly LANs are connected to the Internet and generally the larger the LAN the more likely it is to be connected to the Internet. If the LAN uses TCP/IP then the connection is typically through a firewall. If the LAN uses only a protocol other than TCP/IP then a firewall is not needed but hardware or software that converts the LAN's protocol into TCP/IP is needed to connect to the Internet.

An extranet doesn't have a precise definition but is two or more computers or LANs that are connected to each other via the Internet. Typically the extranet uses TCP/IP to communicate but has some additional layer of security software so that the computers and LANs that are part of the extranet can perform communications between each other that they cannot perform with other computers or LANs connected to the Internet.

A virtual private network (VPN) is similar to an extranet in that two or more computers or LANs are connected via the Internet. Where the definition of an extranet is somewhat vague that of a VPN is quite specific. The computers or networks that are part of a VPN use a common encryption scheme so that all transmissions that cross the public Internet are encrypted. The encryption may be performed by software or dedicated hardware. The intent is to use the widespread and relatively inexpensive connectivity of the Internet to avoid the expense of establishing a Wide Area Network (WAN) while keeping the communications within the VPN as secure as they would be in a WAN. Unless appropriate VPN technology is selected and installed by properly trained and experienced professionals, the VPN may contain significant security weaknesses that can be exploited by persons not authorized to access the VPN.

A WAN is two or more computers or networks that are widely separated geographically and connected with dedicated and presumably secure connections such as leased lines.

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