What is DNS?
By Stephen Bucaro
Have you ever wondered what happens
when you enter, or click on, a web address in your
browser? How does your computer connect to the Web
site you requested? Part of what makes that happen
is the Internet's Domain Name Service (DNS).
Similar to how every telephone has a
unique number, every Web site, or "domain" on the
Internet has a unique Internet Protocol (IP) address.
IP addresses are 32 bit numbers represented by four
bytes separated by dots. Each byte can represent a
number from 0 to 255, therefore the highest IP address
People have difficulty remembering 12
digit numbers, so web sites are are identified by
names like www.sitename.com instead of their IP address.
DNS is a database of domain names and their corresponding
In the beginning, every computer on
the Internet had a list of all the domain names and
their corresponding IP addresses. But that quickly
became unwieldy. Now the domain name database and
domain name to IP address translation is performed
by computers assigned as DNS servers.
Each DNS server has data only about
the domains it is serving. When a computer makes a
request to its DNS, it is possible that the DNS server
doesn't have the data required to answer the request.
Special "root name" servers hold a list of DNS servers
for top-level domains, like .com, .org, .edu etc.
For example, the top-level DNS for .com lists the
DNS servers for domain names ending in ".com".
If a DNS server doesn't have the data
to answer a request, it makes a request to a root-name
server. The root-name server will return the address
of a DNS server where the data can be found.
Each domain name on the Internet is
required to be listed on a minimum of two DNS servers.
This is so if one of the DNS servers goes down, requests
for the domains address can still be answered.
DNS also performs IP address to domain
name translation. This makes it possible for servers
to log accesses and for administrators to perform
certain administrative and security tasks.
Information communicated over the Internet
is broken into "packets" by Transmission Control Protocol
(TCP). TCP attaches the IP address of the requested
domain to each packet so that they can be routed to
the domain. TCP also attaches the IP address of the
requesting computer to the packets so that responses
can be routed back.
When you enter, or click on, a web address
in your browser, the Internet's Domain Name Service
(DNS) translates the web address to the web sites
IP address. This is only part of the story of how
your computer connects to the Web site you requested.
In a future article you'll learn about the amazing
process performed by routers.
Copyright(C)2002 Bucaro TecHelp.
About the Author:
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