As an end-user reporting program, dcdiag is a command-line tool that encapsulates detailed knowledge of how to identify abnormal behavior in the system. Dcdiag displays command output at the command prompt.
Dcdiag consists of a framework for executing tests and a series of tests to verify different functional areas of the system. This framework selects which domain controllers are tested according to scope directives from the user, such as enterprise, site, or single server.
Dcdiag is built into Windows Server 2008 R2 and Windows Server 2008. It is available if you have the Active Directory Domain Services (AD DS) or Active Directory Lightweight Directory Services (AD LDS) server role installed. It is also available if you install the Active Directory Domain Services Tools that are part of the Remote Server Administration Tools (RSAT)