IEEE 802.1X is an IEEE Standard for port-based Network Access Control (PNAC).
This standard provides an authentication mechanism to devices wishing to attach
to a LAN or WLAN.
IEEE 802.1X defines the encapsulation of the Extensible Authentication Protocol
(EAP) over IEEE 802, which is known as EAP over LAN (EAPOL).

802.1X authentication involves three entities, a supplicant, an authenticator,
and an authentication server.

Supplicant: An entity that wants to get authenticated.
Authenticator: A network device, such as an Ethernet switch that authenticates
the Supplicant.
Authentication Server: Typically a host running software supporting the RADIUS
and EAP protocols that provides an authentication service to an authenticator.

Until the Supplicant is authenticated, 802.1X Authenticator allows only EAPOL
traffic through the port to which the Supplicant is connected.
Only after the authentication is successful, the authenticator allows normal
traffic from the Supplicant.