ADSS TSync vs Entra Cross-Tenant Sync: A Comprehensive Comparison

Microsoft

Mar 06, 2025

When managing identities across multiple tenants, organizations often face a crucial decision: should they choose ADSS (Active Directory Synchronization Service) Tenant Sync or Entra Native Cross-Tenant Sync to enable collaboration across tenants?

The ADSS Tenant Sync service for Tenant-to-Tenant Synchronization is designed to maintain a single unified global address list between tenants. It synchronizes and provisions users or contacts between tenants and provisions guest accounts for Azure B2B sharing of applications and resources.
Cross-Tenant synchronization automates creating, updating, and deleting Microsoft Entra B2B collaboration users across tenants in an organization. It enables users to access applications and collaborate across tenants, while still allowing the organization to evolve.

Both solutions aim to streamline identity management, but they differ significantly in terms of architecture, control, security, and overall functionality. Here’s a closer look at each solution, presented with relatable examples to help you make an informed decision based on your organization’s needs.

Architecture and Core Functionality

Imagine you are in charge of a large organization with multiple subsidiaries, each operating under its own Azure AD tenant. You need a solution to synchronize all these identities, but you're unsure where to start.

ADSS Tenant Sync is a managed service provided by Microsoft Consulting - IMS team, utilizing a pull-push model. Here, synchronization rules are configured by Microsoft Consulting, and the ADSS server manages identity synchronization. This model is often preferred for larger, complex organizations, as it centralizes control and often includes expert support. It’s akin to outsourcing a specific task to a trusted third-party expert who sets up and manages the solution for you.

Entra Cross-Tenant Sync, in contrast, is a native feature of Entra ID (formerly Azure AD) that follows a push-based model using SCIM (System for Cross-domain Identity Management). Synchronization happens directly from your source tenant, offering greater control and integration within your existing Microsoft ecosystem. It’s like managing your internal processes with a powerful tool that’s built into your existing system—no need for third-party involvement.

Control, Authentication, and Security

The level of control and the security measures between these solutions differ, particularly when it comes to permissions and access management.

ADSS Tenant Sync requires permissions through Microsoft Graph and Exchange Online, demanding specific admin rights, like Exchange Recipient Admin rights and Write permissions for each object type you want to sync. This can feel like managing a series of security checkpoints where each part of the system requires specific access credentials to function properly.

Entra Cross-Tenant Sync, on the other hand, simplifies authentication by allowing synchronization policies to be configured directly within both the source and target tenants. This reduces complexity and can be managed more easily, especially in organizations that prioritize ease of access and streamlined workflows. It’s more like having a universal access pass for various departments within a company, eliminating the need for multiple levels of clearance.

Data Management, Synchronization, and Filtering

When it comes to data handling, there are key differences in how each solution approaches storage and filtering.

ADSS Tenant Sync utilizes a centralized identity store within Microsoft-owned Azure subscriptions before synchronizing data to target tenants. This approach allows for complex attribute filtering and customization, such as syncing users as guests or contacts with desired attribute flows and even supports distribution list synchronization as contacts. It’s like having a centralized warehouse where all the data is stored and categorized, allowing for flexibility when choosing what data to sync and how to manage it.

In contrast, Entra Cross-Tenant Sync ensures that identities remain within their respective tenants, with no external storage of sensitive identity data. This model is beneficial for organizations concerned about data privacy, as the identities are kept within their home base. Additionally, Entra Cross-Tenant Sync supports syncing users as either external members or guests, depending on configuration. However, it does not support distribution list or contacts synchronization. It’s like keeping all documents in their respective departments to ensure that sensitive information stays within the correct boundaries.

Both solutions support object filtering and attribute-based scoping, but ADSS offers more customization in terms of attribute management, making it more flexible for organizations with intricate requirements.

Cost, API Support, and Suitable Use Cases

Cost and extensibility are crucial factors when considering which solution to adopt.

ADSS Tenant Sync operates as a third-party managed service through Microsoft, with a monthly fee attached. It’s ideal for businesses requiring extensive customization, external guest management, and broader synchronization capabilities. The use of Microsoft Graph and PowerShell APIs for extensibility also makes ADSS suitable for organizations that need advanced integrations and a highly tailored solution.

Entra Cross-Tenant Sync, on the other hand, is natively integrated into the Microsoft ecosystem. It requires a P1 license for each synchronized user, but the overall cost can be lower compared to ADSS, especially for organizations that do not need extensive customization. The solution uses proprietary APIs managed by the Microsoft Entra Product team, offering a more straightforward, integrated experience.

Entra Cross-Tenant Sync is typically more suitable for organizations that prefer an easy-to-manage, cost-effective synchronization solution, without requiring the advanced features of ADSS.

Choosing the Right Solution

Both ADSS Tenant Sync and Entra Native Cross-Tenant Sync have distinct advantages, and the decision between them depends on your organization’s specific needs.

ADSS Tenant Sync is a solid choice for businesses that need advanced features, such as the ability to customize attributes, manage external guests, and support complex synchronization requirements, even if it comes with an additional cost. It’s more suitable for multi-tenant organizations or those working with business partners that require a more tailored solution.
Entra Cross-Tenant Sync is a cost-effective, native option that seamlessly integrates into your existing Microsoft environment. It's ideal for enterprises looking for a simpler, more integrated way to manage multi-tenant synchronization without needing complex customization. This solution works well for organizations that prioritize streamlined workflows and less technical overhead.

In conclusion, whether you choose ADSS Tenant Sync or Entra Native Cross-Tenant Sync depends on your organization’s goals, the level of customization required, and budget considerations. Both solutions offer effective ways to synchronize identities across tenants, and understanding these differences will help you select the one that aligns best with your infrastructure and long-term identity management goals.

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