2.5.3 Domain Membership
Domain membership is the state of trusting a third party (the DC) for identity and authentication information. Any system can conceivably be part of a domain. Windows-based systems can easily be configured to be part of a domain and trust their DC for many tasks. Also, certain configuration changes are made, such as accepting the domain as the authoritative source of time.
Windows-based systems can have local groups that include members from a domain. This allows the member system to manage its resources in the manner most relevant to it and not be completely dependent on the decisions of the domain administrator. A domain administrator can create a domain local group for each resource that exists within a domain, such as file shares or printers, and then add the appropriate global groups from each domain to this domain local group. The domain administrator then assigns the appropriate permissions for the resources to the domain local group.
Joining a domain ultimately distills down to establishing an account on the domain that represents the system joining the domain, and to setting the password (or key) for the account on both the domain and the actual system. In Windows, this process is encapsulated in a domain join function (NetJoinDomain). Several tools, such as WinBind, exist for non-Windows operating systems to join a Windows domain.
All Windows-based systems have a component that manages their relationship with their DC. This component, called Netlogon, maintains the keys that are necessary for ongoing authentication of the member system to the DC. It also creates a general-purpose channel to the Netlogon instance on the DC.<8>
This channel is used by various authentication protocol implementations to redirect an authentication request to (or augment their activities with) their instance on the DC.