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IP NAT Overview, Motivation, Advantages and Disadvantages
(Page 2 of 5)
Indirect Internet Connectivity
One solution to the problems of IP
address space and security was to set up a system where a company's
network was not connected directly to the Internet, but rather indirectly.
Setting up a network this way is possible due to several important characteristics
of how most organizations use the Internet:
- Most Hosts Are Client Devices: The Internet
is client/server based, and the majority of hosts are clients. Client
devices generally don't need to be made publicly accessible. For example,
when using your local PC to access the World Wide Web, you issue requests
to servers and they respond back, but servers don't have any reason
to try to initiate contact with you. Most correspondence is begun by
clients and not servers, by definition.
- Few Hosts Access The Internet Simultaneously:
When you have a large number of hosts on the same network connected
to the Internet, at any given time usually only a small number of them
are trying to access the 'net. It isn't necessary to assume they will
all need to access servers at once. Even while you actively browse the
Web, you pause for a number of seconds to read information from time
to time; you are only accessing the Web server for the time it takes
to perform a transaction.
- Internet Communications Are Routed: Communications
between an organization's network and the Internet go through a router,
which acts as a control point for traffic flows.
The best way to explain why these
attributes matter is to draw an analogy to how telephones are used an
organization, because many of the same attributes apply there. Most
of the telephones in a typical organization are used to let employees
make phone calls out. Usually there is no need to have any way to call
employees directly; instead one system or person can handle all incoming
calls. Only a few employees are ever making a call to the outside
world at any given time. And all calls are routed through a central
point that manages the telephone system.
For these reasons, to save money,
organizations don't run separate public telephone lines to every employee's
desk. Instead, it sets up a telephone system where each employee gets
an extension, which is basically a local telephone number valid
only within the organization. A small number of outside lines is made
available in a pool for employees to share, and the telephone system
matches the inside extensions to the outside lines as needed. A voice
mail system and/or human receptionist handle routing of calls in to
(Yes, some companies have a direct
mapping between extension numbers and real telephone numbers. Don't
make trouble. J)
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Table Of Contents - Contact Us
The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
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