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What is AD bridging? A definitive guide

Active Directory bridging connects non-Windows and cloud services to an AD network. It serves as an identity consolidation service that permits clients to log in across a hybrid infrastructure of Windows, Linux, and Unix servers using their AD credentials.

The definition of Active Directory

Active Directory (AD) is a Windows-only tool for managing access to network resources. It enables administrators to centralize user management and authentication, set granular permissions for different user groups and automate the deployment of services on a network.

But what if you wanted to go beyond Windows with AD? What if you have a hybrid architecture with Windows and

Linux servers spread across different cloud platforms? Could you still use AD to implement centralized authentication and asset management? The answer is yes.

AD bridging is a process that lets non-Windows and cloud-based services, devices and identities latch on to the AD network. It’s a gamechanger for organizations with multi-platform architectures that want to leverage the full potential of AD.

What is AD authentication?

AD authentication is used for the provisioning, authentication and authorization of users and applications on the AD network. Users can log in once using single sign-on (SSO) and get access to all the applications for which they are authorized.

Administrators can use AD to apply security controls and configurations across the infrastructure. They can also define fine-grained Identity & Access Management (IAM) policies to enforce the principle of least privilege, hide sensitive objects from specific users and implement identity lifecycle management.

AD also makes it easy to add and discover services on a network. When administrators publish assets (like printers, computers or files) to an AD network, they instantly become accessible to authorized users. This boosts productivity, fosters scalability and simplifies network management.

What is AD authentication?

AD authentication protocols

Active Directory supports two authentication protocols:


Kerberos is a standardized, interoperable authentication protocol that uses tickets to authenticate and authorize users and nodes on a network. If a client wants to access resources on an AD network powered by Kerberos, they must prove their identity to a key distribution center (KDC).

First, the client must send a ticket-granting request to the KDC, which is encrypted with the user’s password. The KDC then decrypts the request with the same password (all user passwords are known to the KDC) and issues a ticket granting ticket (TGT). The TGT is also encrypted with the user’s password. The client then decrypts the TGT, and requests a service ticket from the KDC, which will allow the user to access the desired service. Once the user client receives the ticket from the KDC, they can forward it to an application server, which ultimately grants access to the service.

Lightweight Directory Access Protocol (LDAP)

LDAP is a cross-platform protocol that can be used for AD authentication in two ways:

  • Simple authentication: In this method, a user’s login credentials are used for authentication. Simple authentication also supports anonymous and unauthenticated access to network resources

  • Simple authentication and security layer: In this method, an additional layer of security is applied to simple authentication (e.g., an organization may combine LDAP and Kerberos for secure access management

What is AD bridging and why would I need it?

AD bridging is a way to bridge the gap between non-AD systems and an AD server. It’s an identity consolidation effort that lets clients use their AD credentials to log in across a hybrid infrastructure of Windows, Linux and Unix servers.

Without bridging, it’s not possible to govern access to non-AD resources in an AD setup. Administrators must resort to creating local privileged accounts on CentOS, Ubuntu or Debian machines. This creation needlessly increases the organization’s attack surface and makes Privileged Access Management (PAM) a hassle.

AD bridging eradicates the need to create multiple user identities for cross-platform authentication. It allows non-AD assets to join an AD network, which can then be seamlessly discovered and accessed by all authorized users.

How does AD bridging work?

An AD bridge acts as an interface between non-AD systems and an AD server. It is responsible for synchronizing users, passwords and policies between the non-AD systems and the AD server. This ensures that the AD server always remains the primary authority for authentication. Here’s how a typical AD authentication flow works with bridging:

  1. The user logs on to their Windows machine
  2. The user tries to access a non-AD service or device. The bridge sends a request to the AD to authenticate and authorize the user
  3. If the user is authenticated and authorized, the bridge opens access to the non-AD system
  4. The user accesses the non-AD system

The benefits of AD bridging

AD bridging offers several benefits for administrators and end users:

  • Creates a single source of truth for all user credentials and decreases your attack surface
  • Performs centralized, consolidated management of all user identities, passwords and network assets
  • Enforces the principle of least privilege by defining granular access policies
  • Offers a seamless login experience to your users, where they can access services running on different operating systems with the same credentials
  • Seamlessly scales your infrastructure across different environments, cloud platforms and operating systems

What is the difference between AD and LDAP?

LDAP is a protocol used to interact with directory services. Active Directory is a directory service that uses LDAP to communicate with assets on a network. Several other directory services and network management solutions also use LDAP.

LDAP is related to AD, just like HTTP is related to Apache Tomcat (a web server). Just like Tomcat uses HTTP to talk to its clients, AD uses LDAP to talk to applications and devices on its network. Other web servers, like Nginx, also use HTTP. Similarly, other directory services, like Oracle Internet Directory, also use LDAP.

Is Active Directory an LDAP server?

Any directory service that supports the LDAP protocol for communication is called an LDAP server. So, by definition, Active Directory is an LDAP server.

Final word

Active Directory is a powerful tool to implement centralized authentication, authorization and asset management. AD bridging empowers you to expand your AD network across your hybrid infrastructure and build a truly consolidated access management system.

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