Networking Basics - What is DNS?
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.