802.1X Protocol for User Authentication | Cisco Exam 400-251

802.1X Protocol

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Which protocol does 802.1X use between the supplicant and the authenticator to authenticate users who wish to access the network?



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A. B. C. D. E.


802.1X is a protocol that provides authentication to devices trying to connect to a network. It is often used in conjunction with other security protocols such as RADIUS, TACACS+ or EAP over LAN to provide a comprehensive security solution.

The protocol uses the Extensible Authentication Protocol (EAP) over LAN to authenticate users. This means that the supplicant (the device trying to access the network) communicates with the authenticator (the access point, switch or router controlling access to the network) using the EAP protocol. EAP is a flexible protocol that supports a wide variety of authentication methods, including password-based, certificate-based, and token-based methods.

The authenticator, acting as a proxy, relays the EAP messages to an authentication server, such as a RADIUS or TACACS+ server. The authentication server is responsible for verifying the user's identity and granting or denying access to the network.

In summary, the correct answer to this question is C. RADIUS, as it is the authentication protocol commonly used with 802.1X. While EAP over LAN is also used for authentication in 802.1X, it is not a protocol used between the supplicant and authenticator, but rather between the authenticator and the authentication server. SNMP and PPPoE are not authentication protocols and are not used in the 802.1X authentication process.