Adomain controller (DC) is aserver[1][2] that responds to security authentication requests within a computernetwork domain. It is anetwork server that is responsible for allowinghost access to domain resources. It authenticates users, stores user account information and enforcessecurity policy for a domain.[3] It is most commonly implemented inMicrosoft Windows environments (seeDomain controller (Windows)), where it is the centerpiece of the WindowsActive Directory service. However, non-Windows domain controllers can be established viaidentity management software such asSamba andRed HatFreeIPA.
The software and operating system used to run a domain controller usually consists of several key components shared acrossplatforms. This includes the operating system (usuallyWindows Server orLinux), anLDAP service (Red Hat Directory Server, etc.), a network time service (ntpd,chrony, etc.), and a computer network authentication protocol (usuallyKerberos).[4] Other components, such as apublic key infrastructure (Active Directory Certificate Services, DogTag,OpenSSL) service andDomain Name System (Windows DNS orBIND) may also be included on the same server or on another domain-joined server.[5]
Domain controllers are typically deployed as acluster to ensure high-availability and maximize reliability. In a Windows environment, one domain controller serves as the Primary Domain Controller (PDC) and all other servers promoted to domain controller status in the domain serve as a Backup Domain Controller (BDC).[6] In Unix-based environments, one machine serves as the master domain controller and others serve as replica domain controllers, periodically replicating database information from the main domain controller and storing it in a read-only format.[7]