[Server 2012R2/2016] Do i need to use adprep or not?

Hans Hard
Hans Hard used Ask the Experts™
Hi, this is my first post.

I plan to upgrade a network with multiple windows server 2012R2 to windows server 2016 like this:

- First I add 2016 servers (which will then be at the 2012R2 AD level) and move functions to them.
- I make some of the 2016 servers to DC (still 2012R2 level).
- I'm demoting and phasing out 2012R2 servers that no longer have any functionality.
- When all 2012R2 servers are disconnected, I raise the AD level to 2016.
- My question is: Now that I'm going to install my first 2016 server and make it to DC, do I need to run "adprep" on it? If so, how?

Exactly what function does "adprep" have? What does it do?

Grateful for any the answers.
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Adprep is used before the first 2016 machine is promoted.

A good guide is here:


Follow those simple steps and you’ll have no issues.


Thanks for the reply.

- I have 4 DC servers today, all 2012R2.
- I add a new 2016 server and make it DC.

So what I don't understand is that:

Will my old 2012R2 servers:
1. Stop managing logins?
2. Continue to manage logins with the 2016 AD level?
3. Explode in a cloud of smoke.
Hi again,

The ADprep will prepare for the 2016 servers, but won’t adversely affect the 2012R2 servers.

When you promote a 2016 DC the 2012 ones will continue as normal (obviously you can set which servers are responsible for which sites/ip ranges as you wish).

When you are happy everything has replicated and your dcdiag tests show everything is happy, you can demote the 2012 servers and raise your domain level to 2016 once the last 2012 server is demoted.

Don’t forget to move your FSMO roles, and ensure DNS, DHCP etc are moved and correctly configured too.
Network Engineer
Adprep makes changes to the AD schema needed by the newer DCs, and makes other changes. It is now run automatically as part of the process of adding in newer DCs. Since Windows 2012 is has been included automatically as part of the domain controller installation process.


Be sure that your domain is using DFSR before you add in any 2016 DCs.
Top Expert 2012

You do not need to run ADprep...it will be executed by Domain Promotion wizard automatically in background. (You may run if the wizard fails during adprep)

ADPrep basically adds the extra attributes to the AD Schema needed for windows 2016

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