The answer is that the RADIUS server is not configured to send the SGT in the Access-Accept message. When a switch performs SGT assignment via 802.1X RADIUS troubleshooting, the RADIUS server must include the Security Group Tag as a vendor-specific attribute (Cisco-AVPair) in the Access-Accept reply; if it does not, the switch defaults the user’s SGT to 0, which is the untagged default. This scenario directly tests your understanding of Cisco TrustSec and the dependency between RADIUS attributes and dynamic SGT propagation, a frequent topic on the ENCOR 350-401 exam. A common trap is assuming the switch’s ‘cts role-based enforcement’ command alone assigns SGTs, but enforcement only works after the tag is received from the server. Remember: SGT 0 means “no tag received,” so always verify the RADIUS policy is pushing the correct attribute.
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 Cisco TrustSec (CTS) with Security Group Access Control Lists (SGACLs) on a campus network. The engineer configures the switch with 'cts role-based enforcement' and assigns SGTs to users via 802.1X. The engineer tests connectivity between a user in SGT 10 and a server in SGT 20. The SGACL permits traffic from SGT 10 to SGT 20, but the user cannot reach the server. The engineer checks 'show cts role-based sgt map' and sees that the user's SGT is 0. 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 configured to send the SGT in the Access-Accept message.
SGT 0 is the default untagged SGT. If the user's SGT is 0, it means the switch did not receive the SGT from the RADIUS server during 802.1X authentication. Option A is correct because the RADIUS server must send the SGT in the Access-Accept message. Option B is incorrect because SGACLs are applied per SGT, not per interface. Option C is incorrect because the switch is configured for enforcement. Option D is incorrect because SGT 0 is not a valid SGT for enforcement; the switch treats it as untagged.
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 configured to send the SGT in the Access-Accept message.
Why this is correct
Correct because the SGT must be assigned by the RADIUS server during authentication.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
The SGACL is applied to the wrong interface.
Why it's wrong here
Incorrect because SGACLs are role-based, not interface-based.
✗
The switch is not configured with 'cts role-based enforcement'.
Why it's wrong here
Incorrect because the engineer configured it, and the command is present.
✗
The user's SGT is 0, which is a valid SGT that denies all traffic.
Why it's wrong here
Incorrect because SGT 0 means no SGT assigned; it does not deny all traffic by default.
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.
Trap categories for this question
Command / output trap
Incorrect because the engineer configured it, and the command is present.
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 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.
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 configured to send the SGT in the Access-Accept message. — SGT 0 is the default untagged SGT. If the user's SGT is 0, it means the switch did not receive the SGT from the RADIUS server during 802.1X authentication. Option A is correct because the RADIUS server must send the SGT in the Access-Accept message. Option B is incorrect because SGACLs are applied per SGT, not per interface. Option C is incorrect because the switch is configured for enforcement. Option D is incorrect because SGT 0 is not a valid SGT for enforcement; the switch treats it as untagged.
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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