Which entity provides common directory services?

Lightweight Directory Access Protocol (LDAP) provides common directory services. Managing Cloud principles explain that LDAP is used to store and retrieve information about users, groups, roles, and permissions in a centralized directory.

LDAP supports authentication, authorization, and identity management by enabling systems to query user attributes and access rights. It is widely used in enterprise and cloud environments to integrate applications with centralized identity services.

RADIUS and TACACS+ are authentication protocols, and DNS resolves domain names to IP addresses. Therefore, LDAP is the correct entity for directory services.