Welcome to the EZSiteMove Resource Article section.
What is DNS? How does it affect me? If you've had a Web site before and have moved or if you have ever bought a domain name, you've probably heard "Your site will be down for 24-72 hours while the DNS propagates." If you are like most people, you've probably thought, "What is this DNS thing? and why does my site have to be down?". Well, we hope the this article will help you understand the basics of DNS. DNS, or domain name server, is a large database of addresses for domain names. Whenever you point your domain to a hosting company, your domain gets listed in a DNS database and your server's address is also listed in that database. Whenever someone wants to go to your Web site, they can look up the server's address in the DNS database. A real life DNS example can be seen in the following interaction between three people, John, Billy, and Steve.  As you can see, John was able to contact Billy, who then was able to get Steve's address so that John could go see him. Now, what would happen if John were to forget Steve's address? He would ask Steve again right?  Even though John forgot Steve's address, he was able to contact Billy, and get Steve's address again. Now, what if Steve moves?  In this case, Steve has moved and John does not know his new address. Billy is too busy to call Steve to get his new address so John has to wait for Billy to call and get Steve's new address. 24 HOURS LATER  24 hours later, John has given Billy plenty of time to call Steve and now John is able to get Steve's new address. DNS in the real world In the real world, DNS also works similar to our example illustrated above. You want to visit a Web site, but you don't know the IP address of the server that is hosting the Web site so you contact your Internet Service Provider's DNS database server. The first time you contact the DNS server, it does not know the IP address of the server for your site so it has to find the IP address for that server. Once the DNS server gets the IP address for the server, it then sends it on to you so that you can get to the Web site. A couple of days later you want to see the Web site again, so you ask the DNS server again for the address. The DNS server thinks, "It's takes a while to get the address and I am busy so let me give you the last address I had for the site, it's probably the same." This assumption by the DNS server is called "caching". DNS servers use caching to save time and resources. It is normaly for you ISP to tell the DNS server wait 24-72 hours before trying to get addresses again. If the address for the Web site is still the same, you will be able to see the Web site. But what if the server has changed it's IP address? You try to go to the Web site, and suddenly there is nothing there. You go back to the DNS server and say, "The Web site moved. It has a new address, can you get it for me?". The DNS server, however, is very busy, so it tells you, "Sorry, I am very busy right now, I can give it to you later. Wait a couple of hours and then ask me again." After some hours you ask the DNS server for the address and the DNS server checks again and then gets you the new address and you again are able to get to the Web site you wanted to see. (This simple tutorial is intented to give a VERY basic overview of propagation issues Web hosting users face when moving Web sites between different servers. It is not intended to offer a complete tutorial on DNS servers and global propagation.) |