Quick Answer
MAC Authentication Bypass (MAB) is the correct choice because it provides a fallback mechanism for devices that lack an 802.1X supplicant and cannot send EAPOL frames, such as printers or IoT sensors. When the switch detects no EAPOL activity within a configurable timeout, it uses the source MAC address of the first incoming frame as the authentication credential, forwarding it to a RADIUS server for verification. On the Cisco DCCOR 350-601 exam, this scenario tests your understanding of port-based authentication methods and the order of operations: 802.1X first, then MAB, then MAC-based port security. A common trap is confusing MAB with port security or assuming all endpoints must support 802.1X; remember that MAB is specifically designed for non-EAPOL devices. Memory tip: "No EAPOL? MAB takes control."
This 350-601 practice question tests your understanding of security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
MAC Authentication Bypass (MAB)
MAB uses the device's MAC address to authenticate against the RADIUS server if no EAPOL is received.
802.1X using RADIUS server
Why wrong: 802.1X requires EAPoL packets from the endpoint.
Port security with sticky MAC addresses
Why wrong: Port security does not provide authentication.
Local authentication with a predefined list of users
Why wrong: Local authentication still requires 802.1X or CLI login.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
MAC Authentication Bypass (MAB)
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
MAC Authentication Bypass (MAB)
Why this is correct
MAB uses the device's MAC address to authenticate against the RADIUS server if no EAPOL is received.
Related concept
Read the scenario before looking for a memorised answer.
802.1X using RADIUS server
Why it's wrong here
802.1X requires EAPoL packets from the endpoint.
Port security with sticky MAC addresses
Why it's wrong here
Port security does not provide authentication.
Local authentication with a predefined list of users
Why it's wrong here
Local authentication still requires 802.1X or CLI login.
Common exam traps
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.
Detailed technical explanation
MAB operates as a fallback mechanism in the 802.1X state machine; when the switch does not detect an EAPOL-Start or EAPOL packet after the 'auth timeout eapol' period (default 30 seconds), it transitions to the MAB state and sends a RADIUS Access-Request with the endpoint's MAC address as the username and password (e.g., '00:11:22:33:44:55'). The RADIUS server must have the MAC address configured as a user; if accepted, the port is placed in the authorized state. A subtle behavior is that MAB can coexist with 802.1X in a 'multi-auth' or 'multi-domain' mode, allowing both 802.1X-capable and non-802.1X devices on the same port.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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FAQ
Security — This question tests Security — Read the scenario before looking for a memorised answer..
The correct answer is: MAC Authentication Bypass (MAB) — 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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