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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 123.123.123.1 and mysite.net.

I host multiple clients on this web server, and I accord each client a DNS address in the form myclient1.mysite.net. 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 myclient99.mysite.net, except that I would like to point that particular client at a different IP address (a different server) with the address 123.123.123.99. 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

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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 ZoneEdit.com, 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 Plus, be sure to remove the old records from your web host (so you don't end up with stale records that are out of date.)

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zoneedit.com 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 mysite.net (as opposed to say, server1.myclient1.mysite.net.)

If I understand you, you are saying you host multiple web sites that are of the form xxx.mysite.net with IP 123.123.123.1 and now you want to have a different web site, myclient99.mysite.net, with IP 123.123.123.99.

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 myclient99.mysite.net pointing to address 123.123.123.99.

Second, be sure you configure your internal firewall so you NAT the external IP address, which I'm guessing is your 123.123.123.99 example, to the internal address (192.168.1.1 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. myclient99.mysite.net is a subdomain of mysite.net –  Dan Carley Jul 9 '09 at 10:34

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