In part 2 of the series we’ve successfully lowered the Forest Functional Level (FFL) and Domain Functional Level (DFL) to Windows Server 2008. The demonstration was completed in a forest where the Active Directory Recycle Bin was not enabled.
In this final part of the series, I will first raise the functional levels back to Windows Server 2016, enable the Active Directory Recycle Bin, and then lower the functional levels. As determined in part 1 of the series, we should be able to lower the functional levels to Windows Server 2008 R2 but not Windows Server 2008.
The Forest Functional Level is set to Windows Server 2008 and the Domain Functional Level of the root domain (root.contoso.com) and a child domain (child1.root.contoso.com) is also set to Windows Server 2008. The remaining child domain (child2.root.contoso.com) is set to Windows Server 2016.
Forest and domain functional levels viewed using Windows PowerShell
Raising the Domain Functional Level (DFL) and Forest Functional Level (FFL)
We’ve determined that the FFL cannot be lower than the DFL of any domain in the forest, which means the DFL of the root and child domain needs to be raised to Windows Server 2016 first. Let’s see what happens when we attempt to raise the FFL to Windows Server 2016 first.
In Windows PowerShell I run the following command:
Set-ADForestMode -Identity root.contoso.com -ForestMode Windows2016Forest -Server root.contoso.com -Confirm:$false
The result is no confirmation or error message which we already know means that the command completed successfully. How is this possible when we haven’t raised the DFL of all the child domains? Let’s confirm this using Windows PowerShell:
The results in PowerShell indicates that while raising the FFL to Windows Server 2016, the DFL of all the domains were automatically raised to Windows Server 2016.
Be careful not to raise the FFL by mistake when planning on changing the DFL of a single domain. This may result in unknowingly raising the DFL of all your domains in the forest.
I should also note that this will fail if all the Domain Controllers are not on the required Operating System version. In the following example I attempted the same action, but a Windows Server 2012 R2 Domain Controller still existed in a child domain. I received an error message:
Set-ADForestMode : The functional level of the domain (or forest) cannot be raised to the requested value, because there exist one or more domain controllers in the domain (or forest) that are at a lower incompatible functional level.
The FFL is raised to Windows Server 2016 and now we can enable the Active Directory Recycle Bin to determine the outcome of lowering the functional levels with the recycle bin enabled.
Enable the Active Directory Recycle Bin
Windows PowerShell can be used to verify if the Recycle Bin is enabled or not.
Get-ADOptionalFeature -Filter ‘name -like “Recycle Bin Feature”‘
We can see from the PowerShell results that the required FFL to enable the Recycle Bin is Windows Server 2008 R2. The EnabledScopes attribute indicates whether the Recycle Bin is enabled or not. The current value is blank which means that the Recycle Bin is not enabled in this forest yet.
The following command is used in PowerShell to enable the Recycle Bin. Replace -Target with the forest root domain Fully Qualified Domain Name (FQDN).
Enable-ADOptionalFeature ‘Recycle Bin Feature’ -Scope ForestOrConfigurationSet -Target root.contoso.com
You will be prompted to confirm your actions. Take note of the warning that this action is not reversible. The Recycle Bin cannot be disabled after it is enabled. No confirmation message is provided to confirm that the Recycle Bin was successfully enabled. Again, no error messages are good.
This should also prevent lowering the Forest Functional Level to Windows Server 2008, because the recycle bin was only introduced with Windows Server 2008 R2.
I will run the Get-ADOptionalFeature command again to verify that the Recycle Bin status in PowerShell again.
The EnabledScopes attribute is no longer blank. This is the indicator that the Recycle Bin is enabled in the forest.
Downgrading the functional levels: Active Directory Recycle Bin enabled
The FFL will now be lowered. The first attempt was to set the FFL to Windows Server 2008 which failed as shown in the screenshot. We then attempt lowering the functional level to Windows Server 2008 R2 which resulted in no error or success message, which indicates the FFL was lowered successfully.
Set-ADForestMode : The functional level of the domain (or forest) cannot be lowered to the requested value
Verify that the FFL is lowered to Windows Server 2008 R2
The DFL of the child domain (child2.root.contoso.com) will now be lowered.
The first attempt was to set the DFL to Windows Server 2008 which failed as shown in the screenshot. The second attempt set the DFL to Windows Server 2008 R2.
Verify the Domain Functional Level. The DFL of the child domain was successfully lowered to Windows Server 2008 R2.
I’ve successfully demonstrated that the Active Directory functional levels can be lowered from Windows Server 2016 functional level, to Windows Server 2008/2008 R2 functional levels, depending on whether the Active Directory Recycle Bin is enabled or not.
The rollback can be completed from any functional level since Windows Server 2008, just keep the Active Directory Recycle Bin in mind when raising the functional level from Windows Server 2008.
If you are planning on upgrading your Active Directory infrastructure, whether this is from Windows Server 2008/2008 R2 or Windows Server 2012/2012 R2, you should now be able to complete this with more confidence. Raising the Active Directory functional levels should be an easier step, knowing you have the option of rolling back to the previous functional level should you experience any unexpected issues.
- Downgrading Active Directory Domain and Forest Functional Levels (Part 1)
- Downgrading Active Directory Domain and Forest Functional Levels (Part 2)
- Downgrading Active Directory Domain and Forest Functional Levels (Part 3)