Active Directory Domain Functions

Active Directory (AD) is a directory service developed by Microsoft for Windows domain networks. It provides a variety of network services and plays an integral role in the administration and security of Windows-based network environments. Among the many features offered by AD, domain functions and security boundaries are particularly important.

Domain functions in Active Directory refer to the functional levels of Active Directory Domain Services (AD DS). These functional levels determine the available capabilities of the domain or forest, including advanced features that were introduced in newer versions of Windows Server. By raising the domain or forest functional level, organizations can utilize these enhanced features, which can include things like improved replication, finer-grained password policies, and additional Active Directory object types.
It's important to note that once a domain or forest functional level is raised, it cannot be lowered without restoring from a backup. Furthermore, raising the functional level can restrict which versions of Windows Server can be used as domain controllers, as older versions may not support the newer features.

In Active Directory, a security boundary is defined as a construct or container where a certain security policy, or set of policies, can be enforced and cannot be overridden. The primary security boundary in Active Directory is the forest.
A forest is a collection of one or more AD domains that share a common schema, configuration, and global catalog, and are linked with two-way transitive trust relationships. Since the forest represents the security boundary, objects such as users, computers, and groups cannot access resources in another forest unless explicit trust relationships are established.
Domains within the forest do not serve as security boundaries, but administrative boundaries. While domains can be managed independently with their own policies and administrators, these configurations can technically be overridden by administrators with forest-level permissions.
It's crucial to properly design and manage your Active Directory structure, taking into account these aspects of domain functions and security boundaries. This will help ensure a secure and efficient network environment.

Domains can be structured in a forest to provide data and service autonomy and to optimize replication with a given region. This separation of logical and physical structures improves manageability and reduces administrative costs because the logical structure is not affected by changes in the physical structure. The logical structure also makes it possible to control access to data. This means that you can use the logical structure to compartmentalize data so that you can control access to it by controlling access to the various compartments.
The data that is stored in Active Directory can come from many diverse sources. With so many different data sources and so many different types of data, Active Directory must employ some type of standardized storage mechanism so that it can maintain the integrity of the data that it stores. In Active Directory, objects are used to store information in the directory, and all objects are defined in the schema. The object definitions contain information, such as data type and syntax, that the directory uses to ensure that the stored data is valid. No data can be stored in the directory unless the objects that are used to store the data are first defined in the schema.
The default schema contains all the object definitions that Active Directory needs to function. However, you can also add object definitions to the schema. While the directory is exposed to you through a logical structure that consists of elements such as domains and forests, the directory itself is implemented through a physical structure that consists of a database that is stored on all domain controllers in a forest. The Active Directory data store handles all access to the database. The data store consists of both services and physical files. These services and physical files make the directory available, and they manage the processes of reading and writing the data inside the database that exists on the hard disk of each domain controller.