Your AD DS forest currently has a Windows Server 2008 R2 forest functional level. You need to perform an in-place upgrade of the domain controllers in east.contoso.com to Windows Server 2025 with minimal administrative effort. What should you do first?

To perform an in-place upgrade of a domain controller to Windows Server 2025, the Active Directory forest and domain functional levels must be at least Windows Server 2016. Since the current forest functional level is Windows Server 2008 R2, you must first raise the domain functional level of the root domain (contoso.com) to Windows Server 2016. This is a prerequisite for raising the forest functional level, which is then required before you can introduce Windows Server 2025 domain controllers. Raising the domain functional level of east.contoso.com to Windows Server 2025 is not possible until the forest functional level supports it. Raising the forest functional level directly to Windows Server 2025 is not possible from 2008 R2; it must be raised incrementally, typically to 2016 first. Extending the schema is part of the process of introducing a newer OS version DC, but it happens automatically when the first new-version DC is promoted, after the functional levels are met.