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Internet
Basic Concepts
The
Internet
IP Addresses
Domains and Sub-domains
Servers
Resources
The
Internet
The Internet
is not the world wide web - nor is it web browsing. This is a
common misconception. Often people will say such things as, "OK,
I am finished with email. Now I want to use the Internet." Email
is something you can do over the Internet - as is web browsing
with Netscape or Internet Explorer.
In other words, the Internet is a collection of computers, networked
together throughout the world, and communicating with each other
through a common language called TCP/IP (Transfer Control Protocol/Internet
Protocol).
The various programs you use recognize TCP/IP, and if everything
is set up correctly, and the computer is correctly connected to
the Internet, all sorts of things can be done, including:
- Web
Crossing
- email
- the
World Wide Web (WWW)
- FTP
- Internet
news
- All
sorts of other services
IP Addresses
In order
to identify all the computers and other devices (printers and
other networked peripherals) on the Internet, each connected machine
has a unique number, called an "IP address". IP stands for "Internet
Protocol," the common language used by machines on the Internet
to share information.
An IP address is written as a set of 4 numbers, separated by periods,
as in
203.183.184.10
This
representation is sometimes referred to as dotted-octet representation
of an IP address.
Here
is some simple mathematics you should know! Each number in this
four-number address can range from 0 through 255. So there are
256 different possible numbers for each part.
Since
there are four parts, so there are a possible 256 X 256 X 256
X 256 = 256 to the 4th power = 4,294,967,296 different possible
machine numbers - over four billion different possible machine
numbers.
This sounds like more than enough addresses to go around, but
IP addresses are beginning to run out.
One single network, for example, might typically have all the
IP addresses starting with 203.183.184 (203.183.184.0 through
203.183.184.255). This has been a customary way of distributing
IP numbers - in chunks of 256 addresses. This is referred to as
a "Class C" network. If numbers are distributed as Class C networks
it means there are only a possible 256 to the 3rd power different
networks - or just 16 million networks - in the whole world.
When you say it like that it doesn't sound like so many networks,
because every office and many offices within offices have their
separate network of computers.
To make
matters worse, many networks don't even use all the 256 IP addresses
available to them, which means that although the IP addresses
are reserved by them they are going to waste.
To help solve this problem, networks have started being assigned
with just 8 or 16 IP addresses. Some special techniques using
local IP addresses that aren't visible to the outside world are
also helping alleviate the strain.
But basically
you should understand that you need a fixed, predefined IP address
assigned to each machine that acts as a server to the outside
world. You can get an IP address assignment from your network
administrator, who receives them in turn from your network's Internet
provider.
Domains
& Sub-domains
Each machine having its own unique IP address is great for machines
communicating with each other, but quite difficult for humans
to remember.
For example, the mail server at Web Crossing Harbor has an IP address
210.226.166.200. You could send email to doug@210.226.166.200,
but it isn't very convenient for a lot of reasons. For one thing,
it is difficult to remember. For another, we might need to move
the mail server to a different machine (with a different IP address)
someday. Then we would have to tell everybody our new IP address
in order to receive mail.
To solve
this problem a system of giving easy-to-remember names to IP addresses
was created. This system is called the domain system. There are
several top-level domains, and all other names fall under that
in a hierarchy of sub-domains.
There are two basic kinds of top-level domains - those based on
type of activity and those based on geographical location:
| Some
Activity Based Domains |
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.com
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Perhaps
the most well-known top-level domain. Originally it was
designated for use by companies and commercial activities.
Now it can be used by anybody for any purpose.
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.org
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Originally
designated for use by nonprofit organizations and individuals,
now it can be used for any purpose.
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.net
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Originally
designated for use by network organizations (such as Internet
providers). Now it can be used for any purpose.
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.gov
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For
governmental organizations in the United States.
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.mil
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For
military organizations in the United States.
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.edu
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For
four-year degree-granting colleges and universities only.
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| Some
Geographic Based Domains |
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.jp
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The
Japan domain
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.us
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The
U.S. domain
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.ca
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The
Canada domain
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.to
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The
Tonga domain
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Some geographic
domains, such as the .to (Tonga) domain, open up their domains
and make them available to anybody in the world.
One common
misconception is that ".com" is a domain for companies located
in the U.S. It isn't - any company in the world can use a .com
domain.
A "host" refers to a fully specified domain, specified completely
down to the specific machine and complete IP address. For example,
webxharbor.com is a sub-domain of the .com domain. www.webharbor.com
is the name of the web server machine in the webxharbor.com domain.
It has a corresponding IP address, but you do not need to know
it because the domain name system keeps track of it for you.
When
the Internet first started out there was just one big list with
all the hosts in the world and their corresponding IP addresses.
But the list quickly got too large and these days the same task
is accomplished with the use of a distributed DNS (domain name
server) system, components of which are located on most networks
throughout the world (including the Web Crossing Harbor office).
Servers
A
server is just a host that serves something. Some examples are:
- web
servers - computers that serve web pages. People connect to
web servers using browsers, such as Netscape Navigator or Internet
Explorer.
- FTP
servers - People connect to them for file transfer, using a
browser or a specialized FTP program, such as Fetch (on a Mac)
or FTP Explorer (on Windows).
- mail
servers - People connect to them to send and receive mail, using
such programs as Eudora, Netscape Mail, Claris Mail and Microsoft
Outlook Express.
- Web
Crossing - a server that lets users create and use online communities,
including forums and chat and other services
Resources
Recommended
Book
- DNS
and BIND, a book by Paul Albitz & Cricket Liu, O'Reilly
& Associates, 1992. Especially Chapters 1 - 4.
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