A global catalog is a domain controller that stores a copy of all Active Directory objects in a forest. It stores a complete copy of all objects in the directory for its host domain and a partial copy of all objects for all other domains in the forest, which are used in typical user search operations. See Microsoft documentation for information on setting up a global catalog.
If you are using a global catalog, use one of these methods to configure your Active Directory user directories:
Configure the global catalog server as the external user directory (recommended).
Configure each Active Directory domain as a separate external user directory.
Configuring the global catalog instead of individual Active Directory domains allows EPM System products to access local and universal groups within the forest.