Why use AD DNS?

My recent article on the need for (and use of) PTR Records in DNS have sparked quite a few questions on using DNS with Exchange Server in general.  The biggest one I get is “Do I need to use Active Directory DNS in order for Exchange Server to work?”  The answer to that one is a bit complicated, but in its simplest form, it boils down to, “No, but you really, truly should.”

Exchange Server 2000 and up required some form of DNS in order to function correctly.  This is mainly because the Windows Internet Naming System (WINS) was “depreciated” starting with that version of Exchange.  What that means is that MSFT officially asked the community to stop using it whenever possible, because it could be removed completely soon.  As it turns out, WINS was phased out in Exchange 2007, though it may still be required for certain Outlook functions.  That’s a topic for a whole different series of blog posts though.

As for DNS integration, it’s quite possible to install Exchange 2000-2007 without having Active Directory DNS configured in your domain, though it isn’t a best practice.  As long as your DNS system can handle Server Name Records (SRV type records), you can successfully use a 3rd-party DNS for your Exchange environment.  There are, however; some good reasons to go with the native Windows Active Directory Integrated DNS solutions:

1 – Exchange can natively talk to Active Directory DNS, and therefore can do some interesting tricks with that DNS platform that it can’t do with 3rd-party DNS.  Things like AutoDiscovery when you move a user to different mailbox servers, or after a recovery operation with Database Portability just don’t work the same way if you’re not using Active Directory DNS.

2 – Many 3rd-Party tools leverage AD DNS to figure out where Exchange resources are.  Note, I’m far from unbiased on this topic, so please see the disclaimer at the end of the blog.  Since many Windows-based tools will natively use AD DNS API calls (like DNSCMD and the newer variants in PowerShell), you may need to make manual updates to your 3rd-Party DNS, or may have to give up functionality.

3 – Many other non-mailbox objects are stored in AD DNS, and must be mapped manually in other DNS systems in order for Exchange to work properly.  You will have to track your Global Catalog servers, Domain Controllers and other resources in order for Exchange to function.

So, as you can see, there are some very good reasons to use Active Directory DNS if you plan on using Exchange Server.  While you may have external DNS records hosted with an ISP or other provider; internally you will be better off with the native DNS solutions in Windows unless you are ready and willing to fine tune your DNS systems and stay on top of it. 

If you are in doubt, you can use the Exchange Best Practices Analyzer to test your environment before you begin to install Exchange.  This tool will test for many things that Exchange needs, including properly configured AD or 3rd-Party DNS systems.