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?