check list and preparation plan before raising domain forest functional level from 2003 to 2008

Hello Experts,

I have a customer who recently upgrade their AD from Windows server 2003 to 2008. The only remaining task , is to raise the forest and domain functional level to Windows 2008. My client wants to no PROS/CONS to raise domain and forest functional level but focus on their internal applications

Client wants to prepare a check list, or action items with the main things to check and validate that their applications are compatible with Windows 2008. I advised them to contact  different vendors and prepare this checklist, but they want from a MS point of view, a second opinion or action plan;

What can be affected that applications stop working?

Where to look at server applications? code, databases, authentication methods, application type and so on?

Can you please enumerate main things to review for each application and validate that MS supports that?

Any known issues or gotchas when you migrate from 2003 to 2008 ?

Please, do not recommend to open an advisory case, I know that you guys have the expertise to provide as much information as you can on this regards

Please, I would like to read thoughts from different teams, AD, Windows server and Consulting teams
Thanks in advance
Jerry SeinfieldAsked:
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Will SzymkowskiSenior Solution ArchitectCommented:
Raising the forest/domain functional levels only affects the domain controllers specifically. It allows you to open new features that were included in the domain or forest functional level release. This will not affect how other applications authenticate to AD etc.

Before you raise the functional levels you need to ensure that your Active Directory is clean from errors in the Event logs and ensure that replication is working as expected, using the following commands.

- repadmin /replsum
- repadmin /showrepl
- repadmin /bridgeheads
- dcdiag /v (checking overall health of the domain)

- you get new features which can help administration

- you cannot promote any older DC's into the enthronement that is less than your functional level (meaning if you have a Forest/domain functional level of 2008 R2, you cannot promote any DC's that are 2000/2003/2008. They all have to be 2008R2 or later.
- this change is irreversible

Another side note is, it is always a best practice to raise the functional level of the Domain first, than the Forest. If you Raise the forest first, All domains beneath get raised to the forest functional level.

Also the link below provides a list of all of the features for each Forest/Domain Raise.


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