I have a doubt regarding the relationship between domains inside of networks and website domains. Websites domain have to be purchased, one goes to one domain registrar, looks to see if the desired domain is available and if available it is possible to purchase the right to use it for a certain period of time. So if one is building a website and wants the website to be found as www.mycompany.com it goes there and purchases the domain mycompany.com.

Now I'm starting to study about Windows Server and Active Directory and there is the idea of domains also. As I understood, forests are security boundaries that isolates AD objects and domains are namespaces inside those forests. So the root domain is used to identify the forest.

Now I've seem people naming those domains like website domains. So for example: mycompany.com could be used. Now this raises some questions:

  1. To use a domain in a forest one needs to purchase the right to use it at a registrar?

  2. One needs to check the availability of the domain on the internet before using it on the forest? What happens if I use the domain mycompany.com and it is already used?

So what is the relationship between those website domains we purchase at registrars and these forest domains we use internally at a network?


When building an Active Directory server, you can name the domain whatever you like. There's no actual requirement to match it up with a web domain; nor are you required to purchase that web domain.

The conflicts that potentially arise are a matter of DNS lookups. For example, if you build an Active Directory domain and call it apple.com (yes, you could actually do this), and someone within the domain tries to go to www.apple.com, then their computer will look for a web server within the local network that is named "www". Computers on your domain assume that all the other computers are called computername.apple.com. When it can't find "www" within the domain then it assumes it doesn't exist. To deal with that you would have to manually add "www" to the DNS which points at the actual internet www.apple.com.

The same thing can happen even if you own the web domain. If you own companyname.com, and you use that with your Active Directory domain, then you'll have to add a DNS entry of "www" to point at your own company's external website.

There may be some debate on the matter, but I think that it's best to have your local domain use something like .internal (some people use .local, but that conflicts with Apple's Bonjour protocol). This will prevent the conflicts mentioned above.

  • 2
    Nah, don't use .internal. Use a domain with a "real" TLD and then delegate a subdomain to your AD DNS services. ad.example.com or the like. – EEAA Apr 25 '15 at 2:56

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