What is DNS?

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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 255.255.255.255.

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 IP
addresses.

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.
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