The answer is that the switch trunk port does not have VLAN 100 allowed. This is the most likely issue because when a wireless LAN controller (WLC) uses 802.1X to authenticate users and assigns them to a specific VLAN, such as VLAN 100, the WLC tags the traffic with that VLAN ID before sending it over the uplink to the switch. If the switch trunk port is not configured to permit VLAN 100, the tagged frames are dropped at the switch, preventing users from accessing network resources even though authentication succeeds. On the ENCOR 350-401 exam, this scenario tests your understanding of how 802.1X wireless VLAN trunk issues arise from mismatched VLAN permissions between the WLC and the switch, a common trap where engineers focus on authentication success rather than Layer 2 connectivity. A helpful memory tip is “Trunk must trust the tag”—if the WLC tags it, the trunk must allow it.
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.
An organization is implementing 802.1X for wireless users using Cisco ISE as the RADIUS server. The network engineer configures the wireless LAN controller (WLC) with 802.1X authentication. Users report that they can connect to the SSID but cannot access any network resources. The engineer checks the WLC and sees that users are authenticated and assigned to VLAN 100. The engineer also checks the switchport connecting the WLC and sees it is a trunk. What is the most likely issue?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The switch trunk port does not have VLAN 100 allowed.
When using 802.1X with WLC, the WLC typically uses VLAN tagging. If the WLC is configured to tag traffic from the SSID with a specific VLAN, the switch trunk must allow that VLAN. Option B is correct because if VLAN 100 is not allowed on the trunk, traffic will be dropped. Option A is incorrect because the users are authenticated, so the RADIUS server is working. Option C is incorrect because the WLC does not need 802.1X on the uplink. Option D is incorrect because the WLC does not use MAB for wireless.
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 RADIUS server is not sending the correct VLAN ID in the Access-Accept.
Why it's wrong here
Incorrect because users are assigned to VLAN 100, so the RADIUS server is sending the VLAN.
✓
The switch trunk port does not have VLAN 100 allowed.
Why this is correct
Correct because the WLC sends tagged traffic on VLAN 100, and the trunk must permit it.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
The WLC is not configured for 802.1X on the uplink to the switch.
Why it's wrong here
Incorrect because the WLC uplink is typically a trunk, not an 802.1X port.
✗
The users' devices are not configured for MAB.
Why it's wrong here
Incorrect because wireless 802.1X does not use MAB.
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.
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 trunk port does not have VLAN 100 allowed. — When using 802.1X with WLC, the WLC typically uses VLAN tagging. If the WLC is configured to tag traffic from the SSID with a specific VLAN, the switch trunk must allow that VLAN. Option B is correct because if VLAN 100 is not allowed on the trunk, traffic will be dropped. Option A is incorrect because the users are authenticated, so the RADIUS server is working. Option C is incorrect because the WLC does not need 802.1X on the uplink. Option D is incorrect because the WLC does not use MAB for wireless.
What should I do if I get this 350-401 question wrong?
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.
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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