Domain/Forest Functional Levels?


need some clarity on this subject, I have been googling and reading the technet stuff but i still cannot completely get my head around this topic?!!

Why would someone raise or lower the domain and forest functional levels? What is the difference between domain and forest? How does it affect the AD?

Can someone please provide me with some real-life examples so i can grasp this topic a little better?



  • srabieesrabiee Member Posts: 1,231 ■■■■■■■■□□
    Upgrading the domain and forest levels adds features that wouldn't otherwise be available. This document lists those features:

    Understanding Active Directory Functional Levels

    These videos may help you understand forests and domain levels a little better:

    Domain Functional Levels

    Forest Functional Levels
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  • kj0kj0 Member Posts: 767
    So I'm on a bit of a roll at the moment...

    A forest\Domain functional level is somewhat a baseline for what your domain controllers are able to do in your environment.

    I don't know in 2012 as I haven't looked into it, but in Server 2008R2, the forest functional level needs to be raised to Server 2008R2 to enable features such as Active Directory Recycle bin. If you do not raise the level, this feature is not available.

    Each Domain Controller is required to be at least Server 2008R2 or higher for this forest functional level.

    If your Forest Functional Level is set at Server 2000, you could potentially have 3 domains under that forest, one domain functional level could be Server 2000, the next 2003 and then 2008. Until you upgrade the Domain controllers in the Server 2000 domain to say 2003, the Domain functional level can not be raised. Once all the Domain functional levels have been raised to say 2008R2, then the forest functional level can be raised.

    The main affect that you will see with raising the levels is the new features that are brought on.

    If you raised the functional level (Forest or Domain) and you have a DC somewhere in there, it will be unable to talk with the domain/forest anymore as it will not be able to understand what is going on.

    Hope that helps clear it up. Anyone able to correct me?
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