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AD 2003 to AD 2012 migration

I have a single Domain forest with three DCs 2003 functional. Need to migrate to AD 2012 R2.

DC01 is Domain Naming, PDC, RID
DC02 is Schema, Infrastructure
DC03 no FSMO but see problem 1 below.

Problem 1 = DC03 is hosting Exchange 2007. It has no FSMO roles. What is the best way to fix this before proceeding? Do I migrate (and upgrade) current exchange 2007 to 2013 on another server, or Demote current exchange server?

Ok, after that problem is fixed, what are next steps?

Your answer needs to assume I have three 2012 R2 member servers, without any configuration whatsoever on them.

Your answer needs to be specific as to what server I need to run what command:

DC01, DC02, DC03 are current 2003 AD DCs

DC04, DC05, DC06 are the 2012 R2 (currently member servers)

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1 Solution
I hope you don't have 2003 Exchange..

Do not migrate directly to 2012 R2 AD

Please Go step by step

Introduce TWO 2008 R2 as domain controllers 1st in domain and then introduce Exchange 2013 SP1 in existing Exchange 2007
Exchange 2007 Should be UR 10 on top of Exchange 2007 SP3
Once you transition Exchange 2007 to 2013, then remove Exchange 2007 server from 2003 domain controller and then demote DC role from server
If you remove AD 1st from server, it will break Exchange

Important: Do not install Exchange 2013 on any domain controller, its not recommended and not required.

Now you can demote rest of 2003 Domain controllers from domain and then introduce 2012 R2 domain controllers
There are some issues from 2003 AD to direct upgrade 2012 R2 recently published

Also I preferred to upgrade 2008 R2 DCs to 2012 R2 (I know you can run directly from 2012 R2 GUI) step by step because then only you would know if face any errors \ issues.
 Instead of directly starting ADDS wizard on 2012 R2 (dcpromo is deprecated with 2012), Logon to 2008 R2 FSMO holder server as domain admins, schema admins  and enterprise admins member, and manually upgrade AD schema with adprep from elevated command prompt. U need to insert 2012 R2 DVD on 2008 R2 DC server and navigate to support\adprep folder I guess to get adprep tool
 Commands could be:
 adprep /forestprep
 adprep /domainprep
 adprep /domainprep /gpprep
 adprep /rodcprep

Once you done above part and AD schema gets replicated to all DCs, you can deploy 2012 R2 DCs without any issues

AHECAuthor Commented:
Please confirm my understanding:

Run in place upgrade on 2007 to 2013 exchange on existing DC, then demote after upgrade?

Otherwise thank you for the nice write up.
AHECAuthor Commented:
Also, the issue you presented on going from 2003 to 2012 is only if both are in existence, if I demote the 2003 and only have 2012 R2 DC's, I am good, no?
You cannot in place upgrade from Exchange 2007 to Exchange 2013
Upgrade is not supported, you must prepare AD schema for Exchange 2013 and then only it can be installed on separate box.

Also you can't demote domain controller that is also Exchange server, it will break Exchange
You need to uninstall Exchange server 1st

For your 2nd comment, you cannot simply demote domain controller where exchange is also installed, it will break Exchange
You need to move Exchange server 1st to another box if you wanted to demote that 2003 DC
What I mean, you need to install another member server and install on top of that one more Exchange 2007.
Then move your send receive settings (Mail flow) to new Exchange server and then you can uninstall the exchange from domain controller
Once you done that you can have 2012 R2 DCs, however still your Exchange 2007 must be running Exchange 2007 SP3 RU13 or later builds

Check below supportability matrix

I think my earlier comment is best suited

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