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Dear people who understand the Domain Name System, please would you be so kind as to explain a few things to me.

Let's assume I have a single publicly accessible web server, with a single IP address and a single DNS address mapped to that IP address. For this example I'll use and

I host multiple clients on this web server, and I accord each client a DNS address in the form On incoming HTTP requests, I use the HTTP host header to determine which client is being accessed.

Let's say I would now like to create, except that I would like to point that particular client at a different IP address (a different server) with the address Is that possible? How should I do this? I believe this is called a sub-domain, is that correct?

EDIT 1 : I should point out that the server is hosted by an Internet Service Provider and they set up the DNS for me originally. I think I would have to go through tech support to make changes. Should I be hosting my DNS records somewhere else?

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3 Answers 3

up vote 1 down vote accepted

I'm adding a second answer to comment on your second question, after your edit.

If your web host is managing your DNS then that is fine; you may need to request they add the A record for you or you may find they provide a web-based facility for you to administer your DNS zone.

However, should you decide to manage your own DNS you can find reliable service at, including an amount of free quota.

If you change your DNS server from the web host you will need to be sure to edit your domain name records with your registrar so the authoritative name server is updated. Plus, be sure to remove the old records from your web host (so you don't end up with stale records that are out of date.)

share|improve this answer is working quite nicely for me thanks! –  Patrick J Collins Nov 9 '09 at 10:45

You'll get some argument about the use of the term "subdomain" with different people. >smile<

What you're asking for, basically, is to create "A" records in a DNS zone for various hostnames (myclient1, myclient2, myclient3, etc) that all refer to the same IP address. Later, you might make additional "A" records (myclient99, myclient100, etc) that refer to a different IP address.

That's all just fine. That's a very typical application of DNS, and won't cause you any problems at all. All you're doing is assigning a different IP address to some of the "A" records you're making. Every "A" record can refer to one (or more, but you don't need that functionality in this case) IP address, and that address doesn't have any relation to what addresses other "A" records refer to.

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It is not a sub-domain (at least not moreso than your existing web sites) because the domain is still (as opposed to say,

If I understand you, you are saying you host multiple web sites that are of the form with IP and now you want to have a different web site,, with IP

This is entirely possible, and is almost trivial (which I mean with no disrespect, but once you know how to do it you will be pleased with the hitherto-unknown power you now have.)

You will need to do two things.

First, edit your public DNS record to add a new A record for pointing to address

Second, be sure you configure your internal firewall so you NAT the external IP address, which I'm guessing is your example, to the internal address ( say.)

What you want to do is certainly a common and regular thing.

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The OP doesn't mention any NAT so it's probably not required. is a subdomain of –  Dan Carley Jul 9 '09 at 10:34

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