The answer is that the RADIUS server is not sending the dACL attributes in the Access-Accept message. This is the most likely cause because a downloadable ACL (dACL) is applied dynamically to the switch port only when the RADIUS server includes the necessary attributes—such as the dACL name or inline ACL definitions—in the successful authentication response. Without these attributes, the switch has no policy to enforce, so the guest session defaults to unrestricted access, allowing traffic to internal servers. On the ENCOR 350-401 exam, this question tests your understanding of how 802.1X guest network dACL troubleshooting hinges on the RADIUS server’s role in delivering the policy; a common trap is assuming the switchport mode or a local ACL is responsible. Remember that the switch is merely the enforcer—it cannot apply a dACL it never receives. A useful memory tip is “No attributes, no restrictions,” meaning if the RADIUS server fails to send the dACL, the guest gets full network access.
CCNP 802.1X and TrustSec Practice Question
This 350-401 practice question tests your understanding of 802.1x and trustsec. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 configuring 802.1X on a Cisco switch for a guest network. The engineer wants to allow guests to access the internet after authentication but restrict access to internal resources. The engineer configures the switch with 'authentication port-control auto' and a downloadable ACL (dACL) from the RADIUS server. After a guest authenticates, the engineer tests connectivity and finds that the guest can access internal servers. What is the most likely cause?
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 RADIUS server is not sending the dACL attributes in the Access-Accept message.
dACLs are applied to the port after authentication to filter traffic. If the dACL is not applied, the guest may have full access. Option D is correct because the RADIUS server must send the dACL name or attributes. Option A is incorrect because the switchport mode does not affect dACL application. Option B is incorrect because the guest is authenticated. Option C is incorrect because the switch does not need a local ACL.
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 switchport is configured as 'switchport mode trunk', which does not support dACLs.
Why it's wrong here
Incorrect because dACLs work on trunk ports as well.
✗
The guest is not being authenticated; the switch is using MAB instead.
Why it's wrong here
Incorrect because the guest authenticated, and MAB would also apply dACLs.
✗
The switch is not configured with 'ip access-group' to apply the dACL.
Why it's wrong here
Incorrect because dACLs are applied automatically by the switch when received from RADIUS.
✓
The RADIUS server is not sending the dACL attributes in the Access-Accept message.
Why this is correct
Correct because without dACL attributes, the switch applies no filter.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
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 RADIUS server is not sending the dACL attributes in the Access-Accept message. — dACLs are applied to the port after authentication to filter traffic. If the dACL is not applied, the guest may have full access. Option D is correct because the RADIUS server must send the dACL name or attributes. Option A is incorrect because the switchport mode does not affect dACL application. Option B is incorrect because the guest is authenticated. Option C is incorrect because the switch does not need a local ACL.
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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