Active Directory Components
Last updated
Last updated
Organizational units help group objects on a smaller scale within the domain. The most common way is to group objects that have similar security and administrative requirements together.When deploying a domain controller, it creates a default OU structure to segment the most common object types, such as users, computers, and domain controllers. The administrator can add, remove, and delete an OU as required.
Once an object is assigned to an OU, it inherits the security settings and permissions that are applied to the OU level. If the same object is moved to a different OU, then it will apply the settings from the new OU, and discard the settings that were applied from the previous OU. OUs also help to delegate administrative control to individuals for specific tasks. Domain administrators have privileges that allow them to manage any object within the domain. But it's possible to create administrators and assign them to manage objects and resources on an OU level. For these administrators, the OU will be the security boundary. They will not be able to modify any other object outside that particular OU.
OUs can also contain object types, such as users, groups, contacts, computers, organizational units, and printers
At a high level, a domain trust establishes the ability for users in one domain to authenticate to resources or act as a security principal in another domain.
Essentially, all a trust does is linking up the authentication systems of two domains and allowing authentication traffic to flow between them through a system of referrals. When 2 domains trust each other they exchange keys, these keys are going to be saved in the DCs of each domains (1 key per trust direction) and the keys will be the base of the trust.
When a user tries to access a service on the trusting domain it will request an inter-realm TGT to the DC of its domain. The DC wills serve the client this TGT which would be encrypted/signed with the inter-realm key (the key both domains exchanged). Then, the client will access the DC of the other domain and will request a TGS for the service using the inter-realm TGT. The DC of the trusting domain will check the key used, if it's ok, it will trust everything in that ticket and will serve the TGS to the client.
It's important to notice that a trust can be 1 way or 2 ways. In the 2 ways options, both domains will trust each other, but in the 1 way trust relation one of the domains will be the trusted and the other the trusting domain. In the last case, you will only be able to access resources inside the trusting domain from the trusted one.
A trust relationship can also be transitive (A trust B, B trust C, then A trust C) or non-transitive.
Different trusting relationships:
Parent/Child – part of the same forest – a child domain retains an implicit two-way transitive trust with its parent. This is probably the most common type of trust that you’ll encounter.
Cross-link – aka a “shortcut trust” between child domains to improve referral times. Normally referrals in a complex forest have to filter up to the forest root and then back down to the target domain, so for a geographically spread out scenario, cross-links can make sense to cut down on authentication times.
External – an implicitly non-transitive trust created between disparate domains. “External trusts provide access to resources in a domain outside of the forest that is not already joined by a forest trust.” External trusts enforce SID filtering, a security protection covered later in this post.
Tree-root – an implicit two-way transitive trust between the forest root domain and the new tree root you’re adding. I haven’t encountered tree-root trusts too often, but from the Microsoft documentation, they’re created when you when you create a new domain tree in a forest. These are intra-forest trusts, and they preserve two-way transitivity while allowing the tree to have a separate domain name (instead of child.parent.com).
Forest – a transitive trust between one forest root domain and another forest root domain. Forest trusts also enforce SID filtering.
MIT – a trust with a non-Windows RFC4120-compliant Kerberos domain.
The global catalog server holds the full writable copy of objects in its host domain, and the partial copy of the objects in other domains in the same forest. The partial replica contains a copy of every object in the forest and the most commonly used attributes in queries.
Applications and users in one domain can query for the objects in another domain (in the same forest) via the global catalog server.
All domain controllers in the domain will not be global catalog servers by default. When installing the first domain controller, it will become the global catalog server, and other domain controllers can be promoted as global catalog servers according to the business requirements. Not every domain controller in the domain needs to be a global catalog server.
The Active Directory site defines a physical topology of the network. Sites can be separate buildings in a campus network, with the branch office in a separate city or even in a separate country.
In Active Directory, there are two types of objects:
Container objects can store other objects in the Active Directory. The domain itself is an example of a container object. The organizational unit is also a container object.
Leaf objects cannot store other objects in Active Directory. A service account is an example of a leaf object.
Every time we create an object in Active Directory, it will be assigned with one or two unique values.
If it is a user or group object, it will receive a globally unique identifier (GUID) and a security identifier (SID). The GUID value will be saved in the objectGUID attribute in each object and the SID value will be saved in the objectSid attribute in each object.
In order to view the GUID and SID values for the user account, the following PowerShell command can be run from the domain controller:
ObjectGUID is a 128-bit value, and is applied to each and every object in Active Directory. This value is not just for the particular Active Directory domain. It is valid globally as well. Once a GUID is assigned to an object, it will be there until the object is deleted from the directory. Modifying or moving objects will not change the value of the GUID. The ObjectGUID attribute value will be published to the global catalog servers. If an application in a domain needs to search for a user object, the best method will be to query using ObjectGUID , as it will give an accurate result.
The SID value for an object is unique within its domain. The SID values associated with the user will be changed if the user object is migrated to another domain. An SID value assigned by one domain will not be accepted by another domain. As soon as a user object is migrated to another domain, a new SID value will be generated. Then, the old SID value will be saved in the sIDHistory attribute. This attribute can contain multiple values. When the system creates a Kerberos ticket for user authentication, it will consider a new SID value and all other SID values listed in the sIDHistory attribute.
This ACL uses the SID values. So, if an object moves to a different domain without sIDHistory , it will lose its access to resources until the ACL is modified. But if the system considers sIDHistory when granting an access token, and if the old SID value is moved over to the new domain, the user is still allowed to access the resources they were assigned.
Can also be used to uniquely identify an object.
There are three types of Active Directory naming attributes that have been used to generate distinguishing names:
organizationName (O) or organizationalUnitName (OU): Organization represents the root-level domain. The OU is where the object is located.
domainComponent (DC): This is the naming attribute for the domain and the DNS. If the DNS name for the domain is rebeladmin.com , the domain components for it will be DC=rebeladmin,DC=com.
commonName (CN): This refers to the objects and containers within the directory.
example:
Here, DC=rebeladmin,DC=com represents the domain name, CN=Users represents the user container, and at the end, CN=Dishan Francis represents the actual object name.
Relative distinguished name (RDN) is a unique value within its parent container. For the preceding example, the RDN for the object is CN=Dishan Francis . Active Directory allows you to have the same RDN for multiple objects within the directory, but all of them need to be in separate containers. It is not permitted to have the same RDN for the object within the same container.
Changing values in the object will not modify the SID value. But if the hierarchical path was changed for an object, the Distinguished Name (DN) will be changed. For example, if you move a user object from one OU to another, the DN value for the user object will be changed.
There are five main Active Directory server roles:
Active Directory Domain Services (AD DS)
Active Directory Federation Services (AD FS)
Active Directory Lightweight Directory Services (AD LDS)
Active Directory Rights Management Services (AD RMS)
Active Directory Certificate Services (AD CS)
Each of these server roles can be installed and configured using PowerShell. The following PowerShell cmdlets can be used to install Active Directory server roles:
| PowerShell cmdlets | Description |
|---|---|
Install- WindowsFeature AD-Domain-Services | AD DS |
Install- WindowsFeature AD FS- Federation | AD FS |
Install-WindowsFeature ADLDS | AD LDS |
Install- WindowsFeature ADRMS | AD RMS - This role has two subfeatures, which are AD Rights Management Server and Identity Federation Support. If required, these individual roles can be installed using |
Install- WindowsFeature AD-Certificate | AD CS - This role has six subroles, which are certification authority ( |
AD FS allows you to share identities between trusted identity infrastructures and is based on a claim-based authorization (CBA) mechanism.
It will trust identities from completely different identity infrastructures, and pass identity information as claims to the organization that hosts the applications. Then, the company that hosts the application will map these claims to claims that the application understands, and make the authorization decisions.
In normal scenarios, if you share a web-based system or application between two identity infrastructures, the partner organizations need to provide two credentials. One credential is to authenticate themselves with their own infrastructure, and the second one is to authenticate themselves with the remote infrastructure. AD FS allows users to have a SSO experience with the application.
AD FS can be hosted in a demilitarized zone (DMZ) in the network, and it will be the only public- facing interface for the applications.
Federation service: The federation servers' hosted federation service will route authentication requests from identities in another identity infrastructure using a federated web SSO method, or from clients through the internet using the web SSO design method.
Federation Service Proxy: Federation proxy servers can be places in the DMZ (the perimeter network segment) and can forward claims to the federation service located in a secure network.
Claims-aware agent: AD FS uses claims to create trust between two identity infrastructures. The claims-aware agent can be used in the application web server to allow queries for AD FS claims. Then, theapplication will use claims in the AD FS security token to make the authorization decision.
Windows Token-based agent: This agent is to be installed on a web server that hosts a Windows Token-based application. It will convert the AD FS security token into a Windows access token, and the application will make an authorization decision based on this.
AD LDS allows you to maintain an independent schema with each AD LDS instance. You can also host multiple AD LDS instances on one computer.
AD DS and AD LDS are both builds based on the same core directory service technologies. AD LDS does not need to depend on the Active Directory domain or forest setup. But in an AD DS environment, AD LDS can use AD DS for authentication.
AD RMS help organizations to protect sensitive data from unauthorized access.
AD RMS contain two roles services:
Active Directory Rights Management Server: This installs the AD RMS server service that requires you to protect the content in an organization.
Identity Federation Support: The AD RMS service also supports integration with AD FS services. It will allow you to protect content shared between two organizations, without setting up AD RMS in both infrastructures. This role service helps integrate AD RMS with AD FS.
AD CS helps organizations build public key infrastructure (PKI) in an easy, cost-effective way. Digital certificates issued by the certification authority can be used to authenticate users, computers, and devices. The certification authority is responsible for receiving certificate requests, verifying certificate requests, and issuing, renewing, and revoking certificates.
There are six role services for AD CS:
Certification authority (CA): Mainly, there are two types of CA. Microsoft named them root and subordinate CA. The placement of these on a network will be dependent on the PKI design. CA is responsible for issuing certificates to users, computers, and devices. It will also manage the validity of certificates.
Certification Authority Web Enrollment: This is a web interface that connects to CA in order to allow users to submit certificate requests, retrieve issued certificates, and download the certificate chain.
Online Responder: This will receive and respond to individual user requests to verify the status of digital certificates.
Network Device Enrollment Service: This service allows non- domain-joined network devices to obtain certificates.
Certificate Enrollment Web Service: This role service works with the Certificate Enrollment Policy Web Service, and allows users and computers to perform certificate enrollment using HTTPS. It also allows certificate enrollment for domain computers or devices that are not connected to the domain, and computers or devices that are not part of the domain.
Certificate Enrollment Policy Web Service: This publishes the certificate enrollment policy information to users and computers.
There are five flexible single master operations roles in the Active Directory infrastructure.
Each of them perform specific Active Directory tasks that other domain controllers in the infrastructure are not permitted to perform. These five FSMO roles are divided into two categories based on their operation boundaries:
| Forest level | Domain level |
|---|---|
Schema operations master | The primary domain controller (PDC) emulator operations master |
Domain-naming operations master | The relative identifier (RID) operations master |
N/A | The infrastructure operations master |
When we create the first Active Directory forest and the first Active Directory domain, all these FSMO roles will be installed in the domain's first domain controller.
we need to check the current FSMO role holder:
move FSMO roles:
Once the move is completed, we can check the role owners again.
If we need to move all five FSMO roles to a new host, we can use the following command:
This role boundary is the forest. This means that an Active Directory forest can have only one schema master. The owner of this role is the only domain controller in the forest who can update the Active Directory schema. In order to make schema changes in the forest, it also needs to have a user account that is a member of the Schema Admins group. Once the schema changes are done from the schema master role owner, those changes will be replicated to other domain controllers in the forest
In an Active Directory forest, the schema master role owner can be found using the following command:
The domain-naming operations master role holder is responsible for adding and removing domains controllers to and from the Active Directory forest. In the Active Directory forest, the domain-naming operations master role owner can be found using the following command:
When you add or remove a domain controller, it will contact the domain- naming operations master role holder via the Remote Procedure Call (RPC) connection, and if it fails, it will not allow you to add or remove the domain controller from the forest. This is a forest-wide role, and only one domain-naming operations master role holder can exist in one forest.
The primary domain controller (PDC) operations master role is a domain- wide setting, which means each domain in the forest will have a PDC operations master role holder. PDC is responsible for time synchronization.
In an Active Directory environment, it allows a maximum of a 5-minute time difference (time skew) between server and client to maintain successful authentication. If it's more than 5 minutes, devices will not be able to be added to the domain, users will not be able to authenticate, and the Active Directory-integrated application will start throwing authentication-related errors.
the PDC role holder is also responsible for maintaining password change replications. Also, in the event of authentication failures, PDC is responsible for locking down the account. All the passwords changed in other domain controllers will be reported back to the PDC role holder. If any authentication failure occurs in a domain controller before it passes the authentication failure message to the user, itwill check the password saved in the PDC, as that will prevent errors that can occur due to password replication issues.
In the Active Directory domain, the PDC role owner can be found using the following command:
The PDC is also responsible for managing the Group Policy Object (GPO) edit. Every time a GPO is viewed or updated, it will be done from the copy stored in the PDC's SYSVOL folder.
The relative identifier (RID) master role is a domain-wide setting, and each domain in the forest can have RID role owners. It is responsible for maintaining a pool of relative identifiers that will be used when creating objects in the domain. Each and every object in a domain has a unique security identifier (SID).
The RID value is used in the process of SID value creation. The SID is a unique value to represent an object in Active Directory. The RID is the incremental portion of the SID value. Once the RID value is being used to generate a SID, it will not be used again. Even after deleting an object from AD, it will not able to reclaim the RID value back. This ensure the uniqueness of the SID value.
The RID role owner maintains a pool of RIDs. When the domain has multiple domain controllers, it will assign a block of 500 RID values for each domain controller. When they are used more than 50%, domain controllers will request another block of RIDs for the RID role owner
In the Active Directory domain, the RID role owner can be found using the following command:
This role is also a domain-wide setting, and it is responsible for replicating SID and distinguished name (DN) value changes to cross-domains.
SID and DN values get changed based on their location in the forest. So, if objects are moved, their new values need to be updated in groups and ACLs located in different domains. This is taken care of by the infrastructure operations master. This will ensure that the changed objects have access to their resources without interruptions.
In the Active Directory domain, the infrastructure operations master role owner can be found using the following command:
