Archive for March 11th, 2010

DNS: The Basics

March 11th, 2010

DNS stands for Domain Name Server, which is an internet server that tells your web browser where to find the pages you request.

To understand how DNS works, you need to know one simple concept: humans like words, computers like numbers.  For example, if you type either of the following into the address bar of your web browser, you’ll get to the same place:

  • 208.17.81.60
  • www.salon.com

208.17.81.60 is the IP address for the online news site Salon.com.  When you type www.salon.com into your browser, the browser queries a DNS server (“do you know where this is?”).  The DNS server will either tell the browser where it is, or forward the request to another DNS server (“I dunno, go ask that guy”).  Within a few hops, your web browser will learn that “www.salon.com” means “208.17.81.60″, and bring up the page for you.

This is how sites “spider” onto the internet.  If your primary DNS server doesn’t know a particular address, it sends the request along to other DNS servers; in most cases, when the query is finally answered by a DNS server that knows what you’re looking for , the servers that sent the request along will overhear the response that your browser receives, and record the record in its own database.  This way, if anyone else asks for it, the server will be able to offer up the information without having to pass the request along.

If DNS servers didn’t operate this way, it could take a very long time for you to reach ANY websites.  Imagine what would happen if only one DNS server in the world knew how to get to Google!  You’d have to stand in a very long line to check your Gmail.

If you have a home internet connection, your ISP is providing you with a DNS server or two (or three).  Some companies provide public DNS servers — Google, for example, provides 8.8.4.4 and 8.8.8.8.  If you mysteriously find yourself able to get to some websites but not others, and you know where in your network your DHCP servers are set (usually in your router), you can try replacing your primary DNS server with a public DNS server to see if it fixes the issue.

For quick and easy DNS tests, you can go to DNSsy.com.