Which protocol utilizes a hierarchical tree database structure to store information about users and resources?

The protocol that utilizes a hierarchical tree database structure to store information about users and resources is LDAP, which stands for Lightweight Directory Access Protocol. LDAP is designed specifically for accessing and maintaining distributed directory information services over an Internet Protocol (IP) network.

In LDAP, the hierarchical structure allows for a flexible and efficient way to organize users and resources, which often reflects a real-world organizational structure. Information is stored in a directory in the form of entries, with each entry having a unique Distinguished Name (DN). This structure makes it easy to navigate and retrieve information such as user credentials, device attributes, and organizational data.

In contrast, other protocols such as RADIUS and TACACS serve different purposes related to authentication and authorization rather than directory services. RADIUS is used primarily for authentication, authorization, and accounting, often in network access scenarios, while TACACS also focuses on providing secure access control but doesn't work with directory structures like LDAP. Kerberos, on the other hand, is a network authentication protocol that uses tickets to grant access to resources but does not focus on the hierarchical storage of user and resource information.

Thus, LDAP stands out for its ability to manage structured data in a way that is particularly suited for directory services.