Hello Gong, Allen,
Thank you for posting in Q&A forum.
You can right click child.b1cloud.smes.sap.corp or atlas.b1cloud.smes.sap.corp and click the Properties, then check Trusts tab and check the trust relationship between child.b1cloud.smes.sap.corp and atlas.b1cloud.smes.sap.corp.
If both child domains are listed under Trusts tab, it seems sub domains trust each others by default.
In a Microsoft Active Directory (AD) environment, a parent domain and its child (sub) domains inherently trust each other in a hierarchical structure. This is known as a transitive trust.
By default, these trusts are two-way and transitive, meaning that a parent domain trusts its child domains and vice versa. This transitive nature extends the trust to all domains within the parent-child hierarchy. If you want to manage or restrict the trust relationships between subdomains, maybe there are possible methods, but it's important to understand the implications as this can significantly impact your domain's functionality and security. Modifying or disabling the default trust relationships between parent and child domains is uncommon and not generally recommended because it can disrupt many AD functionalities.
If you do not want users in one child domain to list users in the other child domain, you can try to block it via permissions on child Domain Controllers. For example: try to set block "Read" permission in the child domain.
I hope the information above is helpful.
If you have any questions or concerns, please feel free to let us know.
Best Regards,
Daisy Zhou
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