What is Active Directory?

We often come across the term Active Directory specially for those working with Windows OS. Here in this article we will discuss very basic concepts and details about Active Directory and why it is important for Windows Server Administrator. Before going into Active Directory let’s see

What is a Directory Service?

A directory service is a software application or system that stores and organizes information about network resources in a hierarchical structure. It is commonly used in computer networks to manage and provide access to various resources, such as files, devices, users, and services.

Directory services act as a central repository or database where information about these resources is stored. They provide a unified and standardized way to locate and manage resources across a network. Users and applications can query the directory service to find specific resources or to perform various administrative tasks.

One of the most widely known directory services is the Lightweight Directory Access Protocol (LDAP), which is commonly used in enterprise environments. LDAP provides a standard method for accessing and managing directory information, and it supports a wide range of applications, including user authentication, authorization, and directory-based searches.

Directory services offer several benefits, like:

  1. Centralized management: Directory services provide a centralized platform to manage and administer network resources. Administrators can control access, assign permissions, and update information in a unified manner.
  2. Scalability: Directory services are designed to handle large-scale networks with a vast number of resources. They can efficiently handle thousands or even millions of entries without sacrificing performance.
  3. Reducing redundancy: By centralizing information about resources, directory services eliminate the need for redundant data storage. This helps reduce data inconsistencies and duplication.
  4. Simplified access control: Directory services allow administrators to define access controls and permissions for resources based on individual users or groups. This simplifies the process of managing user access across the network.
  5. Interoperability: Directory services typically support industry-standard protocols, enabling interoperability with various systems and applications. This facilitates integration between different network services and simplifies the management of diverse resources.

So in conclusion we can think directory service as a central control panel for any organization.

What is Active Directory?

Active Directory is a directory service developed by Microsoft for managing and organizing resources within a networked environment. It provides a centralized database that stores information about users, computers, and other network objects. Active Directory plays a crucial role in controlling and securing access to network resources, enabling efficient administration, and facilitating seamless collaboration among users.

History Of Active Directory:

Active Directory (AD) is a directory service developed by Microsoft, primarily used in Windows-based networks. It was first introduced with the release of Windows 2000 Server in February 2000. The development of Active Directory was driven by the need for a centralized and scalable directory service to manage resources in enterprise environments.

Before Active Directory, Windows networks relied on a different directory service called Windows NT Domain System (NTDS). However, NTDS had limitations in terms of scalability, interoperability, and ease of administration, especially in large and complex networks.

Active Directory aimed to overcome these limitations and provide a more robust and flexible directory service. It was designed to support a hierarchical structure where resources, such as user accounts, computers, and printers, are organized in a logical and manageable manner.

The key features and advancements introduced by Active Directory include:

  1. Domain Structure: Active Directory introduced the concept of domains, which replaced the Windows NT domain model. Domains allowed for better organization and management of resources within a network. Domains can be further grouped into trees and forests, forming a hierarchical structure.
  2. Scalability and Replication: Active Directory introduced multi-master replication, enabling changes made to one domain controller to be replicated to other domain controllers in the network. This replication mechanism ensured data consistency and improved fault tolerance.
  3. Security and Access Control: Active Directory implemented a robust security model, providing granular access control to network resources. It introduced the concept of security groups, allowing administrators to manage permissions at a group level rather than individually for each user.
  4. Integration with DNS: Active Directory integrated with the Domain Name System (DNS) to provide name resolution services within the network. DNS was used for locating and identifying domain controllers, enabling clients to locate resources using friendly domain names.

Over the years, Microsoft continued to enhance and refine Active Directory with each new version of Windows Server. Features like group policies, trust relationships between domains, and the introduction of additional service roles, such as Active Directory Federation Services (ADFS) and Active Directory Lightweight Directory Services (AD LDS), further expanded its capabilities.

What’s in the Active Directory database?

The Active Directory (AD) database is a repository that stores various types of information related to network resources, user accounts, groups, permissions, and other directory objects. It serves as a central store for organizing and managing these objects within an Active Directory domain. The database is stored on domain controllers, which are the servers responsible for managing and replicating the Active Directory data.

Here are some of the key components that can be found in the Active Directory database:

  1. Objects: The database stores information about various objects, including user accounts, computer accounts, groups, organizational units (OUs), and other directory objects. Each object has attributes associated with it, such as the user’s name, email address, group membership, and security settings.
  2. User Accounts: User accounts represent individual users within the network. The database stores information such as the user’s username, password (stored in a hashed format), contact details, group memberships, and access permissions.
  3. Groups: Groups are used to organize and manage collections of users or computers with similar access requirements. Group information, including the group name, members, and group type (e.g., security or distribution), is stored in the database.
  4. Organizational Units (OUs): OUs provide a way to logically organize and manage objects within a domain. OUs can contain users, groups, computers, and other OUs. The database stores information about OUs, including their names, hierarchical structure, and associated objects.
  5. Permissions and Security Descriptors: Active Directory utilizes a security model based on access control lists (ACLs) and security descriptors. The database stores security descriptors that define the permissions and access rights assigned to objects, such as who can read, modify, or delete an object.
  6. Trust Relationships: The database stores information about trust relationships between domains in a forest. Trust relationships define how security information is shared and authenticated between domains, enabling users from one domain to access resources in another.
  7. Replication Metadata: Active Directory utilizes a multi-master replication model, where changes made to one domain controller are replicated to other domain controllers in the network. The database stores replication metadata, including timestamps and identifiers, to track and manage the replication process.
  8. Schema Information: The database contains the Active Directory schema, which defines the structure and attributes of objects that can be stored in the directory. Schema information, such as object classes and their attributes, is stored in the database.  Active Directory schema contains formal definitions of every object class that can be created in the Active Directory forest and every attribute that can exist in an Active Directory object. Active Directory comes with a default schema which is alterable to suit business needs.

It’s important to note that the Active Directory database itself is not directly accessible or modifiable by administrators or users. Instead, administrators interact with Active Directory through management tools and interfaces provided by Microsoft, which facilitate the creation, modification, and retrieval of data stored in the database.

Globally Unique Identifier (GUID) and the Security Identifier (SID) and it’s importance in Active Directory.

In the Active Directory (AD) database, two important identifiers are used to uniquely identify objects and ensure their security: the Globally Unique Identifier (GUID) and the Security Identifier (SID).

  1. Globally Unique Identifier (GUID): A GUID is a 128-bit value that serves as a unique identifier for objects within Active Directory. Each object in the AD database is assigned a unique GUID at the time of its creation. GUIDs are generated using a combination of unique factors, such as the network card’s MAC address and the current timestamp, to ensure their uniqueness across all AD domains and forests. GUIDs remain constant even if an object is moved or renamed within the directory.

GUIDs are used extensively within Active Directory to identify objects and maintain their integrity during replication. They provide a reliable way to track objects across multiple domain controllers and enable proper synchronization of changes made to the objects within the directory.

  1. Security Identifier (SID): A SID is a unique identifier assigned to each security principal within Active Directory. A security principal can be a user account, group account, or computer account. SIDs are used for access control and authentication purposes to determine whether a user or group has permission to access a particular resource.

SIDs are composed of a domain identifier (relative identifier or RID) combined with a domain’s unique identifier (domain SID). The domain SID is common to all security principals within the domain, while the RID portion uniquely identifies each individual security principal within the domain.

When a user logs in or requests access to a resource, their SID is used to determine their access rights based on the permissions and security descriptors associated with the resource. SIDs are an integral part of the security model in Active Directory, ensuring that proper authorization and authentication take place within the network.

Both GUIDs and SIDs play crucial roles in maintaining the integrity and security of objects within the Active Directory database. GUIDs provide a globally unique identifier for objects, enabling their proper tracking and replication, while SIDs ensure secure access control and authentication for users and groups within the network.


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