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I currently have a forest between two forests both running at 03 Forest functional level and domain functional level.<br />
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I would like to upgrade one of the forest and domains to 08 domain and forest functional level. &nbsp;Will this create an problems with the trust. &nbsp;Must I upgrade them both??
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I currently have a forest between two forests both running at 03 Forest functional level and domain functional level.

I would like to upgrade one of the forest and domains to 08 domain and forest functional level.  Will this create an problems with the trust.  Must I upgrade them both??

Forest Trust beween 08 Forest functional level and 03 Forest functional level

Windows Server 2008 and Windows Server 2008 R2, based on the Microsoft Vista codebase, is the last 32-bit server operating system released by Microsoft. It has a number of versions, including including Foundation, Standard, Enterprise, Datacenter, Web, HPC Server, Itanium and Storage; new features included server core installation and Hyper-V.

Windows Server 2008

Windows Server 2003 was based on Windows XP and was released in four editions: Web, Standard, Enterprise and Datacenter. It also had derivative versions for clusters, storage and Microsoft’s Small Business Server. Important upgrades included integrating Internet Information Services (IIS), improvements to Active Directory (AD) and Group Policy (GP), and the migration to Automated System Recovery (ASR).