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I've looked into this on various internet sites and I am still confused.
What is a domain name server? What do they do? Why do some large companies host their own?
I understand that the OTHER DNS (Domain Name System) tells a browser that is requesting a certain domain name what IP address to go to. Is a Domain Name Server a server that answers these requests? If so, aren't they run by an authority?

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This is a bit basic/broad for the SF community. However, a DNS server is any server that provides DNS service, which at the most basic explanation, translates host names such as google.com to IP addresses. – Cheekaleak Aug 4 '12 at 0:20
The wikipedia article is pretty comprehensive. – MDMarra Aug 4 '12 at 0:23

closed as not constructive by Greg Askew, Cheekaleak, MDMarra, Michael Hampton, Mircea Vutcovici Aug 4 '12 at 0:32

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This really doesn't belong here, but I'm feeling nice, so I'll answer.

There are two types of DNS servers: authoritative and recursive resolvers.

An authoritative DNS server is authorized to hand out authoritative answers for a domain. If you have the authoritative DNS server for example.com, it is the one that ultimately tells all other DNS servers what the IP address(es) of example.com is (are). Unless they are configured to behave otherwise, they are not able to cache and recursively resolve DNS queries for zones that they are not authoritative for.

A recursive resolver is what translates a name to IP and caches the response for other computers to access later on. These responses are usually caches, so that the authoritative server(s) for each domain doesn't need to be contacted each time that site is accessed. Having your own local DNS servers is a requirement for Active Directory, and most mid-large companies have their own internal DNS servers so that they can have control over their availability and how they operate, since it's a fundamental link in the chain for internet access.

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