What is DNS?

"DNS" stands for the "Domain Name System". Sometimes, this acronym is used to mean the "Domain Name Service".

A domain name is one of the familiar names that you type into your web browser, such as "www.microsoft.com", or "www.cnn.com". These names are familiar and easy for a human to remember. When you type in one of these names into your web browser, your web browser attempts to connect to the website you specified. To make this connection, your web browser first needs to obtain the IP address of the target website.

An IP address is like a phone number for a computer. It takes the form of four numbers separated by periods (e.g. Every computer on the Internet has at least one of these IP addresses. For example, www.microsoft.com has several IP addresses,,, and www.thehungersite.com has the address

When you type "http://www.microsoft.com" into your browser, your browser needs to look up the IP address of www.microsoft.com. It needs a "directory service" to look up the IP address from the name, just as you would use the phone company's 411 service to look up someone's phone number from their name.

The Directory service that your computer uses to look up IP addresses from domain names is called the "Domain Name Service", or "DNS". When you type in "http://www.cnn.com" into your web browser, your machine contacts a DNS server, asking it to find the IP address for www.cnn.com. The DNS server then contacts other DNS servers on the Internet. These servers determine which DNS server is "authoritative" for www.cnn.com, and then ask one of the authoritative servers to answer the question: What is the IP address of www.cnn.com?

When the System Administrators at cnn.com setup their website and email, they (or their ISP) also setup four authoritative DNS servers. These DNS servers are the "authority" for any questions regarding the domain name to IP address mappings for cnn.com.

These authoritative name servers for www.cnn.com can also answer the following questions:

  • Which hosts are responsible for receiving the email for cnn.com (What are the MX records for cnn.com)?
  • Which name servers are authoritative for cnn.com (What are the NS records for cnn.com)? (You can also use Whois to determine this).
  • Convert a cnn.com domain name into an IP address. For example, they can tell you that europe.cnn.com has the IP address This is called an A record. An "A Record" converts a domain name into an IP address.
  • They can convert an IP address into a domain name. For example, they can tell you that IP address has the name www8.cnn.com. This is called a PTR record. A "PTR Record" converts an IP address into a domain name.
  • They can give you administrative information about the domain, such as the email address of the administrator of the domain. This is called a SOA (Start of Authority) Record. A "SOA Record" contains the email address of the administrator, the serial number of the zone, and several timeouts that are used to manage the cnn.com zone.

Note for Techies: You tell your machine which DNS server to use when you configure your TCP/IP settings, or your machine is told which DNS server to use by a DHCP server. You can see which DNS servers your machine is using by typing "ipconfig /all" at a command prompt.

Problems, Comments, Suggestions? Click here to contact Greg Thatcher

Please read my Disclaimer

Copyright (c) 2013 Thatcher Development Software, LLC. All rights reserved. No claim to original U.S. Gov't works.