ASKER
Active Directory (AD) is a Microsoft brand for identity-related capabilities. In the on-premises world, Windows Server AD provides a set of identity capabilities and services, and is hugely popular (88% of Fortune 1000 and 95% of enterprises use AD). This topic includes all things Active Directory including DNS, Group Policy, DFS, troubleshooting, ADFS, and all other topics under the Microsoft AD and identity umbrella.
TRUSTED BY
[1] Create a cross-forest trust (assumes Windows Server 2003 forest functional level on both sides) and leave each forest as a separate entity.
[2] Migrate the users/resources from abc into bcd or from bcd into abc, using ADMT (free migraton tool from MS) or a paid migraton tool from someone like Quest.
[3] Create a brand-new forest with an entirely new naming context, like efg, and migrate both abc and bcd into the new forest using the migration tools listed in [2].