A. This is by design. Single label domains have always been frowned on and their use strongly discouraged for many reasons, including application compatibility and general usability problems.
The Server 2008 DCPromo wizard gave a warning if you tried to create a single label domain, but it would let you create it. Server 2008 R2's DCPromo wizard, however, will block you, and this will be the policy going forward for future versions.
Note that this doesn't stop you from adding new domains on Server 2008 R2 as child domains to an existing single label domain, because your new domain wouldn't be single label! This is confirmed on Microsoft's site.Related Reading:
- Q. If I add a new writable Windows Server 2008 domain controller (DC) to a hub location, do I need to do anything to redistribute replication connections to my Read Only Domain Controllers (RODCs) in spoke/hub locations?
- Windows Server 2008 Password Policies
- Q. I need to run the Windows Server 2008 R2 domain and forest preparation program, but my existing domain controllers (DCs) are all 32-bit and Server 2008 R2 is 64-bit only. What can I do?
- Q. Do I need to prepare the domain and forest for a Windows Server 2008 R2 domain controller (DC)?
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