Dec 27 2010

DNS - The Air That We Breathe

Posted by Mike Brunt at 6:46 AM Web Servers | .NET | DataBase | Caching | ColdFusion | JRun-J2EE

 

 

How often do we think about air, the air that we breathe?  Hardly at all, unless of course it becomes scarce or non-existent.  It is the same with Domain Name Services (DNS), hardly thought of at all, yet vital to the operation of the Internet and World Wide Web.  In fact many times when it seems we have overall Internet connectivity issues, it can often be DNS.  A tell-tale clue is if services not dependent on DNS are still working; Skype for instance.

DNS serves to translate domain names foo.com into IP Addresses much in the same way that phone books will allow us to find phone numbers from names.  The difference is that no two domain names can be exactly the same.  

In the early days of the Internet, domain names were maintained in local files on each computer system, “host files” as they were called.  As more and more domains were added and more and more servers were added, this system became unwieldy and unmanageable.  So the DNS system we use constantly, began to emerge, in essence a number of distributed databases;  these are called authoritative name servers.  DNS was created in 1983 and in 1984 a Unix based implementation called The Berkeley Internet Name Domain system or “BIND” was created.  In the early 1990’s this was also made available on Windows NT.

In order to ensure that DNS is always available there are multiple servers located all around the Internet and the world, in an interlinked network.  As individual users “clients” we are pointed to the nearest local DNS server and records for every domain and server serving these domains are available to us from there.  As there are very many records to query, a system of caching is used which has a “time to live” value.  The can sometimes cause DNS changes to take time to propagate around the world, hence changes are not initially available everywhere, simultaneously.

Here is a very detailed explanation of the DNS system.

Recently there have been concerns about censorship or control being enforced by Western governments by their seizing domains.  Here is an article relating to that.

 

 

 

 

 

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