I recently saw a post on this and so it got me interested in where this data is stored and where on the MSDN site I could find it. 

I have found that if you ask a company what forest and domain functionality level they are at you will probably get a different answer from each person you ask…so why not get it from the source, query the rootDSE and get the attributes that correspond to the forest and domain levels.

If you are using the Active Directory module for Windows PowerShell in Windows Server 2008 R2 then you can also get this information by using Get-ADDomain and Get-ADForest and it will give you the ForestMode and DomainMode.

Using this same Directory module for Windows PowerShell in Windows Server 2008 R2 you can also use Get-ADRootDSE and look at the forestFunctionality and domainFunctionality.

Here is the blog article that got me looking Permanent Link to Active Directory – Domain and Forest Functional Levels

Here are the links to MSDN’s reference on these values

http://msdn.microsoft.com/en-us/library/cc223273(PROT.10).aspx

http://msdn.microsoft.com/en-us/library/cc223274(PROT.10).aspx

http://technet.microsoft.com/en-us/library/dd378809(WS.10).aspx

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