Server 2025 promotion fails

Question

When I try to promote a Server 2025 running the latest updates I get the error:

Verification of replica failed. The forest functional level is not supported. To install a Windows Server 2025 domain or domain controller, the forest functional level must be Windows Server 2016 or higher.

But when I log into a current domain controller, it states the functional level is 2016.

Answer 1

Hi Daniel Kaliel,

The error message you're encountering—“Verification of replica failed. The forest functional level is not supported”—typically indicates a mismatch between the reported and actual forest functional level, even if the domain controller shows Windows Server 2016.

Please verify the forest functional level using the Active Directory Domains and Trusts console or by running the following PowerShell command:

powershell

Get-ADForest | Select-Object ForestMode

Ensure that both the domain functional level and forest functional level are set to at least Windows Server 2016. If either is below that level (e.g., 2012 R2), promotion of a Windows Server 2025 domain controller will fail.

If the forest level is confirmed to be 2016 and the issue persists, we recommend checking for replication delays or schema inconsistencies across domain controllers. You may also want to ensure that all existing DCs are running supported OS versions.

Let us know if you need help raising the forest level or reviewing your AD environment.

Best regards,

Quinnie Quoc.