A data center engineer is configuring 802.1X authentication on Cisco Nexus switches for wired endpoints. The requirement is to allow traffic on the port even if no EAPOL packet is received from the endpoint (e.g., a printer). Which authentication method should be used?
MAB uses the device's MAC address to authenticate against the RADIUS server if no EAPOL is received.
Why this answer
MAC Authentication Bypass (MAB) is the correct method because it allows a port to authenticate endpoints that do not send EAPOL frames, such as printers or other legacy devices. When no EAPOL is received within a configurable timeout, the switch falls back to using the source MAC address of the first frame as the authentication credential, sending it to the RADIUS server for verification. This satisfies the requirement to permit traffic even without 802.1X supplicant capability.
Exam trap
Cisco often tests the distinction between authentication methods that require EAPOL (802.1X) and those that do not (MAB), and the trap here is that candidates confuse port security or local authentication with network access control, failing to recognize that MAB is the specific fallback for non-EAPOL endpoints.
How to eliminate wrong answers
Option B is wrong because 802.1X using a RADIUS server requires the endpoint to send EAPOL frames to initiate authentication; if no EAPOL is received, the port remains unauthorized and blocks traffic. Option C is wrong because port security with sticky MAC addresses is a Layer 2 access control mechanism that limits the number of learned MAC addresses but does not integrate with RADIUS-based authentication or handle the absence of EAPOL. Option D is wrong because local authentication with a predefined list of users is used for device administration (e.g., SSH or console login), not for port-based network access control of wired endpoints.