Multi-forest support set up

Microsoft Defender for Identity supports organizations with multiple forests, giving you the ability to easily monitor activity and profile users across forests.

Enterprise organizations typically have several Active Directory forests – often used for different purposes, including legacy infrastructure from corporate mergers and acquisitions, geographical distribution, and security boundaries (red-forests). You can protect multiple forests using Defender for Identity, providing you with the ability to monitor and investigate your entire network through a single pane of glass.

The ability to support multiple Active Directory forests enables the following:

  • View and investigate activities performed by users across multiple forests, from a single pane of glass.
  • Improved detection and reduced false positives by providing advanced Active Directory integration and account resolution.
  • Greater control and easier deployment. Improved health alerts and reporting for cross-org coverage when your domain controllers are all monitored from a single Defender for Identity console.

Defender for Identity detection activity across multiple forests

To detect cross-forest activities, Defender for Identity sensors query domain controllers in remote forests to create profiles for all entities involved, (including users and computers from remote forests).

  • Defender for Identity sensors can be installed on domain controllers in all forests, even forests with no trust.
  • Add additional credentials on the Directory services page to support any untrusted forests in your environment.
    • Only one credential is required to support all forests with a two-way trust.
    • Additional credentials are only required for each forest with non-Kerberos trust or no trust.
    • There is a default limit of 30 untrusted forests per Defender for Identity instance. Contact support if your organization has more than 30 forests.

Defender for Identity welcome stage 1


  • The user you configure in the Defender for Identity console under Directory services must be trusted in all the other forests and must have at least read-only permission to perform LDAP queries on the domain controllers.
  • If Defender for Identity standalone sensors are installed on standalone machines, rather than directly on the domain controllers, make sure the machines are allowed to communicate with all of remote forest domain controllers using LDAP.
  • In order for Defender for Identity to communicate with the Defender for Identity sensors and Defender for Identity standalone sensors, open the following ports on each machine on which the Defender for Identity sensor is installed:
    TABLE 1
    Protocol Transport Port To/From Direction
    Internet ports
    SSL (*.atp.azure.com) TCP 443 Defender for Identity cloud service Outbound
    Internal ports
    LDAP TCP and UDP 389 Domain controllers Outbound
    Secure LDAP (LDAPS) TCP 636 Domain controllers Outbound
    LDAP to Global Catalog TCP 3268 Domain controllers Outbound
    LDAPS to Global Catalog TCP 3269 Domain controllers Outbound

Multi-forest support network traffic impact

When Defender for Identity maps your forests, it uses a process that impacts the following:

  • After the Defender for Identity sensor is running, it queries the remote Active Directory forests and retrieves a list of users and machine data for profile creation.
  • Every 5 minutes, each Defender for Identity sensor queries one domain controller from each domain, from each forest, to map all the forests in the network.
  • Each Defender for Identity sensor maps the forests using the “trustedDomain” object in Active Directory, by logging in and checking the trust type.
  • You may also see ad-hoc traffic when the Defender for Identity sensor detects cross forest activity. When this occurs, the Defender for Identity sensors will send an LDAP query to the relevant domain controllers in order to retrieve entity information.

Known limitations

  • Interactive logons performed by users in one forest to access resources in another forest are not displayed in the Defender for Identity dashboard.

Source : Official Microsoft Brand
Editor by : BEST Antivirus KBS Team

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