I have inherited an Active Directory environment that is at the Windows Server 2003 forest and domain functional level.

The DNS domain name has no special characters--it looks like sampledomain.org. The NetBIOS domain name has an underscore in it and looks like sample_domain.

Some have told me that because of the underscore, this domain cannot be "upgraded" to Windows Server 2008 R2.

Documentation that I have seen on TechNet seems to simply state that a DNS domain name cannot have an underscore in it. I see nothing that states the NetBIOS domain name would prevent me from upgrading to 2008 R2 domain controllers and raising the forest/domain functional levels.

Which is correct?

3 Answers 3


It is entirely possible to have a NetBIOS name different from the first label of the DNS's full domain. At my old job, we had the following (changed):

  • NetBIOS: example
  • DNS: ad.it.example.com
  • AD Domain Name: ad

Logins could use either "EXAMPLE\username" or "username@ad" syntax for login prompts, and technicians could use either "example" or "ad" for the "Domain" line when domaining a workstation. Just before I left we managed to get it to the 2008 functional-level. You shouldn't have problems with an underscore-bearing NetBIOS name.

  • How do you make DNS different from AD Domain? I can't figure out what to google for. I'm starting fresh.
    – tladuke
    Commented Mar 23, 2012 at 23:53
  • 1
    @tladuke The same way you'd put an AD domain at 'example.com' named 'example'. The domain-name is the last DNS label, 'ad' in the above. Sub-domains in such a tree would be things like 'europe.ad' and 'swiss.europe.ad' and such like, all with 'it.example.com' tacked onto the DNS it uses. 'ad' is just the root domain of the AD tree, which is itself a DNS sub-domain of something else. AD Domain != DNS Domain, though they do look a lot alike.
    – sysadmin1138
    Commented Mar 24, 2012 at 0:01

I'd go with the docs on this one. Some scanning on my own of the technet fora likewise shows this to specifically not be a problem.

Worst case - try forestprep and domainprep and let them try to complain. No complaints -> no problems.

  • I agree that there's no problem with having an underscore in the NetBIOS name but the "worst case" approach you've suggested is, in my opinion, dangerous. While there have been few if any issues raised by schema upgrades for forest and domain prep, doing it in the live environment to just try is not the best way. If the proverbial did hit the fan, the OP would be in it up to his neck in no time if there were problems. I recommend uSlackr's approach, build a test env and document the procedure before implementing it in live, have very up to date backups and KNOW how to restore them.
    – Lewis
    Commented Apr 5, 2012 at 13:41

I recommend using a virtual machine to create an isolated AD DC with a similar config (keep it off the network.) Attempt to upgrade the VM.

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