A client-side extension (CSE) is an integral component of enterprise group policy administration that applies Group Policy to users or endpoint systems.
In Windows 2000 and later environments, Group Policy is designed using server-side and client-side elements. The server-side elements include a user interface for creating each Group Policy Object (GPO). When a client system logs into the environment through Active Directory (AD), the client-side elements -- typically implemented as a series of .DLL files -- receive and interpret the appropriate GPOs in order to make corresponding changes to the client system.
Each CSE is identified by a unique 128-bit number called a global unique identifier (GUID). As the server initializes Windows Server, the list of GPOs is passed to each endpoint's CSE. The CSE, in turn, uses the GPO list to apply appropriate policies. GUIDs are also recorded by the CSE into event logs, so any problems or issues with GPO processing can be isolated and reviewed by its GUID.
GUIDs for CSEs are typically recorded as a series of 32 hexaadecimal characters. For example, a CSE such as A2E30F80-D7DE-11d2-BBDE-00C04F86AE3B indicates Internet Explorer settings. Other common CSEs include script, security, software installation, folder redirection and other components, and each one will have its own GUID.
As third-party programs and other Microsoft services install other CSEs, the GUIDs are registered in the system's registry. Parameters for each GUID are recorded as registry values. Thus, systems administrators tasked with troubleshooting group policy problems must often investigate registry errors or verify registry entries to locate GPO problems.