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
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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