Microsoft Defender for Identity architecture

Microsoft Defender for Identity monitors your domain controllers by capturing and parsing network traffic and leveraging Windows events directly from your domain controllers, then analyzes the data for attacks and threats. Utilizing profiling, deterministic detection, machine learning, and behavioral algorithms Defender for Identity learns about your network, enables detection of anomalies, and warns you of suspicious activities.

Defender for Identity architecture:

Defender for Identity architecture topology diagram

This section describes how the flow of Defender for Identity's network and event capturing works, and drills down to describe the functionality of the main components: the Defender for Identity portal, Defender for Identity sensor, and Defender for Identity cloud service.

Installed directly on your domain controller or AD FS servers, the Defender for Identity sensor accesses the event logs it requires directly from the servers. After the logs and network traffic are parsed by the sensor, Defender for Identity sends only the parsed information to the Defender for Identity cloud service (only a percentage of the logs are sent).

Defender for Identity components

Defender for Identity consists of the following components:

  • Defender for Identity portal
    The Defender for Identity portal allows the creation of your Defender for Identity instance, displays the data received from Defender for Identity sensors, and enables you to monitor, manage, and investigate threats in your network environment.

  • Defender for Identity sensor
    Defender for Identity sensors can be directly installed on the following servers:

    • Domain controllers: The sensor directly monitors domain controller traffic, without the need for a dedicated server, or configuration of port mirroring.
    • AD FS: The sensor directly monitors network traffic and authentication events.
  • Defender for Identity cloud service
    Defender for Identity cloud service runs on Azure infrastructure and is currently deployed in the US, Europe, and Asia. Defender for Identity cloud service is connected to Microsoft's intelligent security graph.

Defender for Identity portal

Use the Defender for Identity portal to:

  • Create your Defender for Identity instance
  • Integrate with other Microsoft security services
  • Manage Defender for Identity sensor configuration settings
  • View data received from Defender for Identity sensors
  • Monitor detected suspicious activities and suspected attacks based on the attack kill chain model
  • Optional: the portal can also be configured to send emails and events when security alerts or health issues are detected

Note

If no sensor is installed on your Defender for Identity instance within 60 days, the instance may be deleted and you'll need to recreate it.

Defender for Identity sensor

The Defender for Identity sensor has the following core functionality:

  • Capture and inspect domain controller network traffic (local traffic of the domain controller)
  • Receive Windows Events directly from the domain controllers
  • Receive RADIUS accounting information from your VPN provider
  • Retrieve data about users and computers from the Active Directory domain
  • Perform resolution of network entities (users, groups, and computers)
  • Transfer relevant data to the Defender for Identity cloud service

Defender for Identity sensor features

Defender for Identity sensor reads events locally, without the need to purchase and maintain additional hardware or configurations. The Defender for Identity sensor also supports Event Tracing for Windows (ETW) which provides the log information for multiple detections. ETW-based detections include Suspected DCShadow attacks attempted using domain controller replication requests and domain controller promotion.

Domain synchronizer process

The domain synchronizer process is responsible for synchronizing all entities from a specific Active Directory domain proactively (similar to the mechanism used by the domain controllers themselves for replication). One sensor is automatically chosen at random from all of your eligible sensors to serve as the domain synchronizer.

If the domain synchronizer is offline for more than 30 minutes, another sensor is automatically chosen instead.

Resource limitations

The Defender for Identity sensor includes a monitoring component that evaluates the available compute and memory capacity on the domain controller on which it's running. The monitoring process runs every 10 seconds and dynamically updates the CPU and memory utilization quota on the Defender for Identity sensor process. The monitoring process makes sure the domain controller always has at least 15% of free compute and memory resources available.

No matter what occurs on the domain controller, the monitoring process continually frees up resources to make sure the domain controller's core functionality is never affected.

If the monitoring process causes the Defender for Identity sensor to run out of resources, only partial traffic is monitored and the health alert "Dropped port mirrored network traffic" appears in the Defender for Identity portal Health page.

Windows Events

To enhance Defender for Identity detection coverage related to NTLM authentications, modifications to sensitive groups and creation of suspicious services, Defender for Identity needs to analyze the logs of the following Windows events: 4776,4732,4733,4728,4729,4756,4757,7045 and 8004. These events are read automatically by Defender for Identity sensors with correct advanced audit policy settings. To make sure Windows Event 8004 is audited as needed by the service, review your NTLM audit settings.

Next steps