Which protocol is used for directory services, often including user authentication?

The protocol used for directory services, which often includes user authentication, is LDAP, or Lightweight Directory Access Protocol. LDAP is specifically designed to access and maintain distributed directory information services over an internet protocol network. It enables organizations to store information about their users, such as usernames, passwords, and attributes in a directory, which simplifies the process of authentication and access control.

LDAP is widely implemented for user authentication scenarios because it allows for the querying and modification of directory services. This is particularly useful in environments that require centralized management of user accounts and security credentials, enabling streamlined access to network resources.

In contrast, while L2TP, L2F, and PPTP are all protocols related to virtual private network (VPN) connections, they do not serve the purpose of directory services or user authentication in the same way that LDAP does. These protocols focus on creating secure tunnels for data transmission rather than managing user data and authentication processes.