What are Trust Relationships in Active Directory?

 

Introduction

In multi-domain or multi-forest environments, Trust Relationships in Active Directory enable secure and controlled access to resources across different domains or forests. Trust relationships allow for resource sharing without duplicating user accounts or compromising security.

In this blog post, we’ll explore what trust relationships are, the different types of trusts, and how they enhance security and collaboration between domains and forests.

What is a Trust Relationship?

A Trust Relationship in Active Directory is a secure link established between two domains or forests that allows users in one domain to access resources in another. Trusts enable resource sharing while maintaining distinct security boundaries between domains.

Trust relationships are essential in organizations with multiple domains or forests, as they allow for centralized management of resources and users without requiring duplicate accounts in every domain.

How Trust Relationships Work

When a trust relationship is established, it creates a pathway for authentication requests to flow between the trusting and trusted domains. For example, if Domain A trusts Domain B, users in Domain B can authenticate and access resources in Domain A based on the permissions set by administrators.

However, trust relationships do not automatically grant access to resources. Access still requires proper permissions to be set on the target resource, and users must authenticate according to the security policies of the trusted domain.

Types of Trust Relationships

Active Directory supports several types of trust relationships, each serving different scenarios:

1. Parent-Child Trust:

   • This trust is automatically created between a parent domain and its child domain. For example, if you have corp.com and a child domain hr.corp.com, the trust is automatically configured when the child domain is created.

2. Tree-Root Trust:

   • A Tree-Root Trust is automatically established between the root domains of two trees in the same forest. This allows resource sharing across trees within the same forest.

3. External Trust:

   • An External Trust is a manually created trust between domains in different forests or domains in separate AD infrastructures. This type of trust is often used in mergers or acquisitions where organizations need to share resources but maintain distinct directories.

4. Forest Trust:

   • A Forest Trust is manually created between two Active Directory forests. This enables users in one forest to access resources in another forest, and vice versa. Forest Trusts are used when organizations have separate AD forests but want to enable collaboration between them.

5. Shortcut Trust:

   • A Shortcut Trust is manually created between two domains within the same forest to reduce the time it takes for authentication requests to travel between domains. This is useful in large forests with deep domain hierarchies.

6. Realm Trust:

   • A Realm Trust is established between an Active Directory domain and a non-Windows Kerberos realm. This type of trust enables interoperability with other systems that use Kerberos authentication.

Trust Directions

Trust relationships can be one-way or two-way:

• One-Way Trust: In a one-way trust, one domain trusts another domain, but the reverse is not true. For example, Domain A trusts Domain B, but Domain B does not trust Domain A.

• Two-Way Trust: In a two-way trust, both domains trust each other, allowing users from either domain to access resources in the other domain.

Transitive vs. Non-Transitive Trusts

• Transitive Trust: A transitive trust allows the trust relationship to extend beyond the two domains. For example, if Domain A trusts Domain B, and Domain B trusts Domain C, Domain A also implicitly trusts Domain C.

• Non-Transitive Trust: A non-transitive trust only exists between the two domains it was established between. It does not extend to other domains.

How Trust Relationships Enhance Security

Trust relationships are vital for maintaining security in a multi-domain or multi-forest environment. By using trusts, organizations can centralize resource access while still maintaining distinct security boundaries between domains.

Key security features of trust relationships include:

• Selective Authentication: Administrators can enforce selective authentication to control which users from a trusted domain can access resources in the trusting domain.

• Conditional Forwarding: Trusts allow for conditional forwarding of authentication requests, ensuring that only the necessary authentication information is shared between domains.

• Trust Direction: By configuring one-way trusts, organizations can control the flow of authentication and limit the exposure of sensitive resources to other domains.

Best Practices for Managing Trust Relationships

1. Use Forest Trusts for Collaboration: If you need to enable resource sharing across multiple forests, use forest trusts instead of creating multiple external trusts, as they are easier to manage and more secure.

2. Limit Trust Direction: Use one-way trusts where possible to limit the exposure of sensitive resources to external domains or forests.

3. Enable Selective Authentication: For high-security environments, enable selective authentication to control exactly which users can access resources across trust boundaries.

4. Monitor Trust Health: Regularly check the health of trust relationships using tools like Active Directory Domains and Trusts or PowerShell to ensure they are functioning properly.

Conclusion

Trust Relationships in Active Directory are essential for organizations with multiple domains or forests. They provide a secure and flexible way to share resources across domains while maintaining security boundaries. By properly configuring and managing trust relationships, organizations can enable collaboration and centralized resource access without compromising security.