Question 452 of 2,015

802.1X and TrustSec →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the switch is not configured to send EAP-Request/Identity packets, likely because the 'dot1x timeout tx-period' is too long or missing. This is correct because 802.1X authenticator configuration relies on the switch actively prompting the supplicant; by default, the switch sends an EAP-Request/Identity only once every 30 seconds, and if the laptop’s supplicant does not receive this prompt, it will not initiate authentication, resulting in a timeout or failure. On the ENCOR 350-401 exam, this tests your understanding of the 802.1X authentication flow and the authenticator’s role in initiating EAP exchanges—a common trap is assuming the supplicant always starts the process, when in fact the switch must send the first EAP frame. A helpful memory tip: “The authenticator must talk first—if the switch is silent, the supplicant won’t listen.”

CCNP 802.1X and TrustSec Practice Question

This 350-401 practice question tests your understanding of 802.1x and trustsec. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 network engineer is deploying 802.1X on a Cisco switch for a mixed environment of Windows laptops and IP phones. The engineer configures the switchport with 'authentication port-control auto' and 'dot1x pae authenticator'. After connecting a Windows laptop, the switch logs show 'Authentication failed' for the laptop. The engineer verifies that the RADIUS server is reachable and the laptop's supplicant is configured correctly. What is the most likely cause of the authentication failure?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1mediummultiple choice

Study the full AAA explanation →

A
The switch lacks 'aaa new-model' configuration.
Why wrong: Incorrect because AAA is needed for RADIUS authentication, but the RADIUS server is reachable, so AAA is likely configured.
B
The switch is not configured to send EAP-Request/Identity packets; the 'dot1x timeout tx-period' is too long or missing.
Correct because without proper EAP initiation, the supplicant may not respond, leading to authentication failure.
C
The switchport is configured as 'switchport mode trunk' instead of 'switchport mode access'.
Why wrong: Incorrect because 802.1X can work on trunk ports, and the issue is authentication failure, not VLAN mismatch.
D
The RADIUS server is not configured with the correct shared secret.
Why wrong: Incorrect because the engineer verified the RADIUS server is reachable, and shared secret issues would cause different errors.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The switch is not configured to send EAP-Request/Identity packets; the 'dot1x timeout tx-period' is too long or missing.

The scenario describes a common issue where 802.1X is configured but the switch is not sending EAP requests because it is waiting for a trigger. Without 'dot1x timeout tx-period', the switch sends EAP-Request/Identity only once every 30 seconds by default. The laptop's supplicant may not initiate the process if it doesn't receive a prompt. Option B is correct because the switch must be configured to send EAP requests to start the authentication. Option A is incorrect because 'aaa new-model' is required for AAA but not the direct cause of the failure. Option C is incorrect because the switchport mode is not specified; 'switchport mode access' is typical but not the issue. Option D is incorrect because the RADIUS server is reachable per the engineer's verification.

Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
The switch lacks 'aaa new-model' configuration.
Why it's wrong here
Incorrect because AAA is needed for RADIUS authentication, but the RADIUS server is reachable, so AAA is likely configured.
✓
The switch is not configured to send EAP-Request/Identity packets; the 'dot1x timeout tx-period' is too long or missing.
Why this is correct
Correct because without proper EAP initiation, the supplicant may not respond, leading to authentication failure.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
The switchport is configured as 'switchport mode trunk' instead of 'switchport mode access'.
Why it's wrong here
Incorrect because 802.1X can work on trunk ports, and the issue is authentication failure, not VLAN mismatch.
✗
The RADIUS server is not configured with the correct shared secret.
Why it's wrong here
Incorrect because the engineer verified the RADIUS server is reachable, and shared secret issues would cause different errors.

Common exam traps

Common exam trap: authentication is not authorization

Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.

Detailed technical explanation

How to think about this question

This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.

KKey Concepts to Remember

Authentication checks who the user is.
Authorization controls what the user is allowed to do after login.
Privilege levels affect access to EXEC and configuration commands.
AAA, TACACS+ and RADIUS can separate login success from command access.

TExam Day Tips

Do not assume successful login means full administrative access.
Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
Separate login problems from permission problems before choosing the answer.

Key takeaway

Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.

Real-world example

How this comes up in practice

A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.

What to study next

Got this wrong? Here's your next step.

Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related 350-401 questions on access control and AAA configuration.

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FAQ

Questions learners often ask

What does this 350-401 question test?

802.1X and TrustSec — This question tests 802.1X and TrustSec — Authentication checks who the user is..

What is the correct answer to this question?

The correct answer is: The switch is not configured to send EAP-Request/Identity packets; the 'dot1x timeout tx-period' is too long or missing. — The scenario describes a common issue where 802.1X is configured but the switch is not sending EAP requests because it is waiting for a trigger. Without 'dot1x timeout tx-period', the switch sends EAP-Request/Identity only once every 30 seconds by default. The laptop's supplicant may not initiate the process if it doesn't receive a prompt. Option B is correct because the switch must be configured to send EAP requests to start the authentication. Option A is incorrect because 'aaa new-model' is required for AAA but not the direct cause of the failure. Option C is incorrect because the switchport mode is not specified; 'switchport mode access' is typical but not the issue. Option D is incorrect because the RADIUS server is reachable per the engineer's verification.

What should I do if I get this 350-401 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Authentication checks who the user is.

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Same concept, more angles

1 more ways this is tested on 350-401

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. Consider the following configuration on a Cisco IOS-XE switch: interface GigabitEthernet1/0/1 switchport mode access authentication port-control auto dot1x pae authenticator dot1x timeout tx-period 5 spanning-tree portfast What is the effect of this configuration?

medium

A.The port will immediately transition to forwarding state and then wait for authentication.
✓ B.The switch will act as an 802.1X authenticator and the port will be unauthorized until a successful authentication.
C.The port will be placed in a VLAN assigned by the RADIUS server after authentication.
D.The switch will act as a supplicant and respond to EAP requests from an upstream authenticator.

Why B: This configuration enables 802.1X authentication on the interface with the authenticator role, sets the transmit period to 5 seconds, and enables PortFast to avoid STP delays. The 'authentication port-control auto' command puts the port in unauthorized state until authentication succeeds.

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