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Difference between A record and Subdomain

Posted on 2012-12-26
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So, I'm curious about the difference between a subdomain and an A record in DNS. I've never had any issues, but I'm curious about how/why "A record" and "Subdomain" seem to be interchangeable for some people.

For example,

example.com (domain)

www.example.com (www is an "A" record within example.com)

server.america.example.com (server is an "A" record within the subdomain of "america.example.com).

This makes sense to me. However, I'm finding some people who argue that in the example "www.example.com", that www is actually a subdomain and not an A record.

Is there actually a difference between the two or is the difference simply in implementation?

Thanks,
Tim
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Question by:timmr72
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by:davorin
davorin earned 125 total points
ID: 38721827
A record defines FQDN (full qualified domain name) of the host which belongs to a certain domain.
Subdomain does not define a single host (or computer/server). Hosts do part of (sub)domain.
(Sub)domain is just administrative entity.
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footech earned 125 total points
ID: 38722278
I don't think there's much to add to the answer, but sometimes restating info in a different way helps understanding.
When you get right down to it, an A record is a specific type of DNS record.  It references a FQDN to an IP.  CNAME records also reference FQDNs, and so do some others.  I think I've actually seen a web host/registrar (might have been 1and1) that when you were creating a record inside a domain it prompted you to specify the subdomain.  IMO, "subdomain" can be used informally in a few scenarios, but it doesn't seem to have a specific definition.  I'd call it more a term for an administrative unit than anything else.  A child domain (which you could also call a subdomain), is a domain in its own right, so denver.co.us.americas.gov could either refer to a (sub)domain or to a specific host - until you add some context to it it isn't clear and probably doesn't matter.
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by:timmr72
ID: 38722290
Thank you both.
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