RADIUS

RADIUS is the industry-standard protocol for centralized Authentication, Authorization, and Accounting (AAA) across distributed network access points.

Network engineers rely on RADIUS (Remote Authentication Dial-In User Service) to manage secure access via a client-server architecture. When a user connects to a NAS (Network Access Server), the device forwards credentials to a central RADIUS server (like FreeRADIUS or Cisco ISE) using UDP port 1812. The server validates the request against a backend database (LDAP or Active Directory) and returns specific configuration parameters (VLAN assignments or time limits). This protocol remains the backbone of enterprise Wi-Fi (802.1X) and VPN security by decoupling user identity from physical hardware.

https://datatracker.ietf.org/doc/html/rfc2865