Upgrading domain controllers - compatibility

Question

I am trying to track down official documentation for domain controller compatibility. We are behind the ball and still have some 2008R2 DC's, I want to make sure that i can go to 2019 both with just the OS compatibility and also the functional level upgrade, what are the oldest client OS for workstations and servers that each functional level can support. We have some applications that vendors are still requiring older OS's so I need to make sure i don't end up kicking anything off the domain as we upgrade.

I have been trying to find a document that shows each functional level with the oldest OS each one supports but my searches have not tracked something down yet.

Answer 1

Hello,

Thank you for posting here.

Here are the answers for your references.

Q1: I want to make sure that I can go to 2019 both with just the OS compatibility and also the functional level upgrade, what are the oldest client OS for workstations and servers that each functional level can support.

A1: From the link below, we can see:

1.Functional levels determine the available Active Directory Domain Services (AD DS) domain or forest capabilities. They also determine which Windows Server operating systems you can run on domain controllers in the domain or forest. However, functional levels do not affect which operating systems you can run on workstations and member servers that are joined to the domain or forest.

2.For Windows Server 2019, There are no new forest or domain functional levels added in this release.

So currently, the highest domain/forest functional level is Windows server 2016 (not Windows server 2019). And no matter what the forest or domain functional level is, we can add machines with any oldest client OS or server OS to the domain.

The link below can help you understand the issue of functional level and operating system version better.
https://learn.microsoft.com/en-us/windows-server/identity/ad-ds/active-directory-functional-levels#windows-server-2019

Q2: We have some applications that vendors are still requiring older OS's so I need to make sure i don't end up kicking anything off the domain as we upgrade.

A2: You can try to migrate the applications to new version of the clients or servers if possible.
The version of the application you use is related to the supported OS version by the application itself, so if you are using a Microsoft application, we can check the corresponding support version, and then do the migration appropriately.
For other brands of applications, you are advised to consult the corresponding developers or engineers.
so if it it is possible, you can download the corresponding version of the application on the new version of the workstation to avoid the situation where the applications cannot be used.
Because as you know, the old clients OS (such as Win 7 or earlier OS) or servers OS (such as 2008 R2 or earlier OS) are not supported by Microsoft.

Hope the information is helpful.

Best Regards,
Daisy Zhou