RADIUS uses main message types:
Access-Request. The authenticator sends credentials to RADIUS for verification.
Access-Accept. RADIUS approves access. May include attributes like VLAN assignment or session timeout.
Access-Reject. Authentication failed. The port stays blocked.
Access-Challenge. RADIUS needs more information. This enables multi-step authentication like one-time passwords or certificate verification.
Accounting messages (Start, Stop, Interim-Update) track session duration and data usage for auditing.