1.3.3.3 Group Policy Extension Settings Retrieval
The last step of policy application is the actual retrieval of settings. In this step, the client uses its computed list of GPOs that contain different classes of settings to invoke a protocol sequence that is specific to each class of settings called a Group Policy extension (for example, the Group Policy: Registry Extension Encoding, specified in [MS-GPREG]). Such an invocation is done by using a unique client-side extension GUID (CSE GUID) in the GPO to identify the class. The Group Policy client then executes the plug-in code (which is associated with that CSE GUID on the client) that obtains the Group Policy extension's settings from the GPO through a protocol exchange with the Group Policy server and that interprets those settings in a specific manner. The Group Policy client itself has no knowledge of the internal details of specific Group Policy extensions.
These Group Policy extensions retrieve the settings of their specific classes that are stored in each GPO, typically by using LDAP to access the Active Directory storage portion of the GPO on the Group Policy server or by reading or writing the file system portion of the GPO on the Group Policy server, or both. After the settings are retrieved, the Group Policy extension plug-in on the client can interpret the settings and enforce the behaviors they specify.