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Is it possible to create a new windows root domain named subdomain.domain.local in the same forest where the root domain domain.local already exist? Please note I am not saying to add a child domain to domain.local, but to create another root domain in the same forest.

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Don't know the answer, but wouldn't this violate the "principle of least confusion"? Sysadmins (and probably parts of code, even non-MSFT code) would assume that it is in fact a subdomain in AD, which might cause all sorts of trouble down the line. – rmalayter Feb 1 '12 at 17:12
100% agree, I would never support this configuration, this configuration comes out from a discussion with my boss – Danilo Brambilla Feb 1 '12 at 17:17
up vote 2 down vote accepted

An Active Directory forest cannot have two root domains.

From a DNS perspective, you can certainly delegate to a separate root at that name, if that's what you're looking to achieve. You can also set up a cross-forest trust between the separate roots, if that's what you're aiming for. But, a single forest only has one root domain.

Can you give some more details about what your goal is? We may be able to provide some alternative recommendations.

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agree, my mistake. The new domain would not be a root one. At the moment this Company has a single 2003 domain forest named say domain.local. They asked as to upgrade to 2008 R2. My opinion is to keep a single domain architecture as Microsoft best practice, add a couple on new 2008 R2 DC after schema upgrade, then move the Operation Masters and finally remove old DCs. As Company also wants to achive 'isolation' between server farm and clients, my boss suggested to create a second domain called subdomain.domain.local and move servers there, leaving client hosts on the old structure. – Danilo Brambilla Feb 1 '12 at 17:31
but the idea is to create this new domain not as child domain but as a new one into the same forest (?!?). I know, it sounds a bit confusing. I think a single domain would be fine, and a good OU organization would fit Company needs – Danilo Brambilla Feb 1 '12 at 17:33
This is why bosses shouldn't be allowed to design AD forests. – RobM Feb 1 '12 at 17:48
@DaniloBrambilla Gotcha - well those are pretty much the options; new forest, or child domain. – Shane Madden Feb 1 '12 at 18:10

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