What is RADIUS servers?

RADIUS (Remote Authentication Dial-In User Service) is a networking protocol that provides centralized authentication, authorization, and accounting (AAA) management for users who connect to a network service. It is commonly used by ISPs, enterprises, and universities to manage network access for dial-up, VPN, wireless, and other network connections. A RADIUS server authenticates users against a database (such as Active Directory or LDAP), authorizes their access to network resources, and tracks their usage for accounting and billing purposes.