What Is RADIUS?
RADIUS (Remote Authentication Dial-In User Service) is a networking protocol designed to centralize AAA — authentication, authorization, and accounting — for network access over UDP ports 1812 and 1813.
How RADIUS works
When a user attempts to connect to an enterprise Wi-Fi network, VPN, or switch port, the network hardware (acting as a RADIUS client) offloads the credential check to the central RADIUS server.
- >Authentication: the RADIUS server verifies the user's credentials against a backend database or directory.
- >Authorization: if valid, the server returns an Access-Accept packet containing policy instructions (e.g., "Assign this user to VLAN 20 and apply ACL X").
- >Accounting: the server logs session activity, including logon/logoff timestamps, assigned IP addresses, and data usage for security audits.
Why RADIUS
Without RADIUS, administrators would have to manually create and manage local user accounts across every individual switch, router, AP, and firewall on a network. RADIUS eliminates this operational burden by providing a single point of access control, powering technologies like 802.1X (port-level authentication) and dynamic network segmentation.
RADIUS centralises the three A's: , and , over UDP ports and . It commonly powers port-level authentication.