What is Active Directory and its Logical Structure

Active Directory

The Active Directory directory service is a distributed database that stores and manages information about network resources, as well as application-specific data from directory-enabled applications. Active Directory allows administrators to organize objects of a network (such as users, computers, and devices) into a hierarchical collection of containers known as the logical structure. The top-level logical container in this hierarchy is the forest. Within a forest are domain containers, and within domains are organizational units.

Benefits of Logical Structure

• Increased network security. The logical structure can provide security measures such as autonomy for individual groups or complete isolation of specific resources.
• Simplified network management. The hierarchical nature of the logical structure simplifies configuration, control, and administration of the network, including managing user and group accounts and all network resources. 
• Simplified resource sharing. The logical structure of domains and forests and the relationships established between them can simplify the sharing of resources across an organization.
• Low total cost of ownership. The reduced administration costs for network management and the reduced load on network resources that can be achieved with the Active Directory logical structure can significantly lower the total cost of ownership. 

Domain

Domains are container objects. Domains are a collection of administratively defined objects that share a common directory database, security policies, and trust relationships with other domains. In this way, each domain is an administrative boundary for objects. A single domain can span multiple physical locations or sites and can contain millions of objects.

Domain Tree

Domain trees are collections of domains that are grouped together in hierarchical structures. When you add a domain to a tree, it becomes a child of the tree root domain. The domain to which a child domain is attached is called the parent domain.

A child domain might in turn have its own child domain. The name of a child domain is combined with the name of its parent domain to form its own unique Domain Name System (DNS) name such as software.pcprompt.net. In this manner, a tree has a contiguous namespace.

Forest

A forest is a complete instance of Active Directory. Each forest acts as a top-level container in that it houses all domain containers for that particular Active Directory instance. A forest can contain one or more domain container objects, all of which share a common logical structure, global catalog, directory schema, and directory configuration, as well as automatic two-way transitive trust relationships. The first domain in the forest is called the forest root domain. The name of that domain refers to the forest, such as pcprompt.net. By default, information in Active Directory is shared only within the forest. In this way, the forest is a security boundary for the information that is contained in that instance of Active Directory.

OU

Organizational units are container objects. You use these container objects to arrange other objects in a manner that supports your administrative purposes. By arranging objects in organizational units, you make it easier to locate and manage them. You can also delegate the authority to manage an organizational unit. Organizational units can be nested in other organizational units.

You can arrange objects that have similar administrative and security requirements into organizational units. Organizational units provide multiple levels of administrative authority, so that you can apply Group Policy settings and delegate administrative control. This delegation simplifies the task of managing these objects and enables you to structure Active Directory to fit your organization’s requirements.