Foreign Security Principals (FSPs)

Foreign Security Principals (FSPs) are special objects in Active Directory that represent security principals (such as users, groups, and computers) from trusted external domains. When a trust relationship is established between two Active Directory domains or forests, FSPs are created in the trusting domain to represent security principals from the trusted domain.

Here are some key points about Foreign Security Principals (FSPs) in Active Directory:

1. Purpose: FSPs serve as placeholders for security principals from trusted domains. They allow administrators in the trusting domain to assign permissions and rights to users and groups from trusted domains without having to create local copies of those principals.

2. Creation: When a trust relationship is established between two domains or forests, FSPs are automatically created in the trusting domain to represent security principals from the trusted domain. These FSPs are created in the ForeignSecurityPrincipals container within the domain's System container.

3. SID Mapping: Each FSP contains a reference to the security identifier (SID) of the corresponding security principal in the trusted domain. This allows the trusting domain to resolve permissions and access rights for objects owned by security principals from the trusted domain.

4. Limitations: FSPs have some limitations compared to native security principals in the trusting domain. For example, FSPs cannot be members of universal groups or used in certain scenarios that require native security principals.

5. Management: FSPs are managed by the Active Directory infrastructure and are typically not directly managed by administrators. However, administrators can assign permissions and rights to FSPs just like they would for native security principals.

6. Replication: FSPs are replicated between domain controllers within the trusting domain to ensure consistency. Changes to FSPs, such as the addition or removal of trust relationships, are replicated using standard Active Directory replication mechanisms.

Overall, Foreign Security Principals (FSPs) play a crucial role in facilitating trust relationships between Active Directory domains or forests. They enable administrators to manage permissions and access rights across trusted domains without duplicating security principals. Understanding FSPs is important for administrators involved in managing trust relationships and access control in multi-domain or multi-forest Active Directory environments.