Knowledgebase: DNS
What is DNS
Posted by Chris Atherton on 17 July 2012 12:07 PM

DNS stands for domain name service.  DNS works in a similar way to a telephone directory.  Think of your domain name as an entry in one of these directories, with different extensions listed under the domain for the difference services used, such as an extension for email, your website or any sub-domains.   Each ISP (your internet connectivity supplier) has their own version of this telephone directory.  When you navigate to, or to continue the analogy call a domain in your browser or email client, your ISP (or which ever DNS server your computer is set to use) will look up the number in the directory and pass it back to your browser.  Your browser then rings the number listed (IP address) to connect to the server where the content is hosted.

 

Your ISP holds a copy of this information which speeds up the process of finding your domain.  As such this speeds up the loading of your website or the delivery of emails. 

 

If your ISP doesn’t have a copy of the domain information it goes looking for it where the domain is registered.  It looks specifically for what is known as the ‘nameserver’, these are like mini directories just for your domain. 

 

When the ISP finds the details it is looking for, it stores a copy of the data.  Each record in this directory has a time limit until it expires, or to use the IT term; a ‘time to live’ (TTL).  When this time to live expires, the ISP goes looking for an update of your information once more, back to the nameservers.  Each nameserver record also has a time to live.  When this expires your ISP will go to the registry where your domain is registered and lookup the nameserver information once more.

 

As you can imagine all this activity occurs for every domain around the world.  So in order to not overload the systems most TTL’s are set between 15 minutes and an hour, sometimes more.

 

When you change a DNS record it takes time for all ISP’s around the world to be updated with the new details.  This is called DNS propagation.  DNS propagation can take up to 48 hours to fully complete.  Think of dropping a stone into a mill pond, it takes time for that ripple to reach all the parts of the pond.  The same is true with DNS propagation.

 

For more information on DNS please see our article on ‘What are DNS Records’:

 

http://www.ehosting.com/support/index.php?/Knowledgebase/Article/View/77/40/what-are-dns-records


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