Which of the following is a key component of a directory services server?

VPN (Virtual Private Network) provides secure remote network access but is not a core component of a directory services server itself.

RIS (Remote Installation Services) is a deprecated Microsoft technology for deploying operating systems over a network, which is a separate function from core directory services.

LDAP (Lightweight Directory Access Protocol) is the primary protocol used by client applications to access and communicate with directory service servers, such as Active Directory, for querying and updating directory information. It defines the operations for searching, adding, deleting, and modifying directory entries.

RAS (Remote Access Service) enables remote users to connect to a network, but it is not a direct component of a directory service's core functionality for managing user and resource information.