You can only set the DFL to Windows Server 2012 when you create a new domain tree on a Windows Server 2012-based computer

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Remember in the Beta of Windows Server 2012 (then called Windows Server “8”) you couldn’t specify the Windows Server 8 Forest Functional Level (FFL) in the new Active Directory Domain Services Configuration Wizard when you created a new forest?

My fellow Directory Services MVP Mike Kline wrote a blogpost on this issue, where he explains choosing the Windows Server 8 functional levels resulted in the following error during the Prerequisites Check:

The specified value '5' is not valid for the argument 'Domain level'

Last week, Microsoft KnowledgeBase article 2747704 was written. This article suggests a new bug exists in Windows Server 2012, that prevents admins from choosing a Domain Functional Level different than Windows Server 2012 when they add a new domain tree to an existing forest.

The screenshot below shows the inability to choose anything else from within the Active Directory Domain Services Configuration Wizard:

Isn’t that ironic?

The workaround given by Microsoft is to either:

Use a Windows Server with an earlier release of Windows Server (for instance Windows Server 2008 R2 with Service Pack 1) to create the new domain tree.
Use the Install-ADDSDomain PowerShell cmdlet to create the new domain tree in Windows Server 2012 and specify the required value for the domain functional level with the –DomainMode switch. Possible values for this switch are:

Win2003
Win2008
Win2008R2
Note:
More information on the Install-ADDSDomain Cmdlet can be found here.

As an example, here is a PowerShell one-liner that will create an Active Directory domain tree, called domain2.local with the Windows Server 2008 R2 Domain Functional Level in the Location1 site of the domain.local forest, equipped with both the DNS Server and the Global Catalog role:

Install-ADDSDomain -NoGlobalCatalog:$false
-CreateDnsDelegation:$false –Credential (Get-Credential)
–DatabasePath "E:\Windows\NTDS" -DomainMode "Win2008R2"
-DomainType "TreeDomain" -InstallDns:$true
-LogPath "F:\Windows\NTDS" -NewDomainName "domain2.local"
-NewDomainNetbiosName "DOMAIN" -ParentDomainName "domain.local" -NoRebootOnCompletion:$false -SiteName "Default-First-Site-Name"
-SysvolPath "F:\Windows\SYSVOL" -Force:$true

I’m sure you can modify this PowerShell one-liner to your needs.

a blog by Sander Berkouwer