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Intranets
Chapter 7
How the Domain Name System (DNS)
Works
CONTENTS
The heart of intranets and the Internet is the Domain Name System
(DNS), the way in which computers can contact each other and do
things such as exchange electronic mail, or display Web pages.
The Internet Protocol (IP) uses Internet address information and
the DNS to deliver mail and other information from computer to
computer.
You may not realize that every IP address on the Internet is actually
a series of four numbers separated by periods (called dots), such
as 163.52.128.72. It would be impossible for you to remember these
numeric addresses when you wanted to send e-mail or visit a site.
Also, because sometimes numeric IP addresses change, you would
never be able to know every time those numeric addresses change.
The DNS solves these problems.
The DNS creates a hierarchy of domains or groups of computers
and it establishes a domain name (also known as an Internet address)
for each computer on an intranet or the Internet, using easily
recognizable letters and words instead of numbers. Major domains
also have the responsibility for maintaining lists and addresses
of the domains that are underneath them. That next level of domains
is responsible for the following level down and so on.
An Internet address is made up of two major parts separated by
an @ (pronounced at) sign. The first part of the address-to the
left of the @ sign-is the user name, which usually refers to the
person who holds the Internet account, and is often that person's
login name. The second part of the address, to the right of the
@ sign, is the host name or domain name, which identifies the
specific computer where the person has an Internet mail account.
Often, the domain name will be the name of the intranet.
The rightmost portion of the domain section of the address identifies
the largest domain and kind of organization where the person has
his or her address. Common domains in the United States are com
for commercial; edu for education; gov for government; mil for
military; net for network (companies and groups concerned with
the organization of the Internet); and org for organization. Outside
the United States, only two letters are used to identify the domains,
such as au for Australia; ca for Canada; uk for United Kingdom;
and fr for France.
Typically, an intranet will have its own domain, often the name
of the company that owns it. Mail to be delivered begins with
a request to an intranet nameserver first. If the host receiving
the mail is on the intranet, the nameserver will be able to translate
the Internet address into the numeric IP address, and so the mail
can be delivered. If the host isn't on the intranet, the nameserver
may have to contact an Internet nameserver. It does this by contacting
an Internet root domain name server, which then tells it which
Internet name server to contact. That Internet nameserver will
be able to translate the Internet address into the numeric IP
address, and again, the mail will be able to be delivered.
- When a particular URL needs to be contacted, the address with
the URL must be matched to the true IP address. Your Web browser
first goes to a local DNS server on the company intranet to get
this information. If the IP address is a local one, the DNS server
will be able to resolve the URL with the IP address. It will send
the true IP address to your computer.
- Your Web browser now has the true IP address of the place
you're trying to locate. It uses that IP address and contacts
the site. The site sends you the information you've requested.
- If the information you have requested isn't on your intranet-and
if your local DNS server doesn't have the IP address-the intranet
DNS server must get the information from a DNS server on the Internet.
The intranet DNS server contacts what's called the root domain
server, which is maintained by a group called the InterNIC.
The root domain server tells the intranet server which primary
nameserver and secondary nameserver has the information about
the requested URL.
- The intranet DNS server now contacts the primary nameserver.
If the information cannot be found in the primary nameserver,
the intranet DNS server contacts the secondary server. One of
those nameservers will have the proper information. It will then
pass the information back to the intranet DNS server.
- The intranet DNS server sends the information back to you.
Your Web browser now uses the IP address to contact the proper
site.
When someone on an intranet wants to contact a location-for example,
to visit a Web site-they will type in an address, such as www.metahouse.com.
In fact, though, the Internet doesn't truly use these alphanumeric
addresses. Instead, it uses IP addresses, which are numerical
addresses, in four 8-bit numbers separated by dots, such as 123.5.56.255.
A DNS server, also called a nameserver, matches alphanumeric addresses
to their IP addresses, and allows you to contact the proper location.
Contact
reference@developer.com with questions or comments.
Copyright 1998
EarthWeb Inc., All rights reserved.
PLEASE READ THE ACCEPTABLE USAGE STATEMENT.
Copyright 1998 Macmillan Computer Publishing. All rights reserved.
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