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i dont know what A records do.

and are they necessary for a web server to host multiple domains and how are they related to DNS?

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+1 because I'm not a fan of "browse-by vote-downs." Most likely they voted you down because you can look at a variety of direct answers to this with a simple Google search. - The Question if they are necessary for multiple domains is however relevant and fairly original. –  Joshua Enfield Sep 28 '10 at 14:52

3 Answers 3

up vote 11 down vote accepted

An A record is a DNS record.

Specifically it's the DNS record that maps from a hostname to an IP address. Every URL that contains a domain name must go via an A record to find the IP address of the server that's hosting it.

See RFC 1034 and RFC 1035.

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This is a bit of a loaded question, but I'll try to give a brief conceptual description. An A record is a translation of a Domain name to an IP address. When a computer queries out to find a domain (google.com, yahoo.com, etc), it doesn't find it by the domain, but the IP; the DNS server gives the IP that it has in the A record when it receives the query for the domain and the computer then navigates to that address. It is of course a lot more complicated than that, but that is a high level description of what service an A record performs.

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a quick example

your-domain.org. IN A 123.456.789.012 ;this is the public ip

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