The answer is that VLAN 30 must be created in the switch’s VLAN database and explicitly added to the trunk’s allowed VLAN list. This is correct because a trunk port will only forward traffic for VLANs that both exist in the switch’s global VLAN configuration and are permitted by the `switchport trunk allowed vlan` command; without the `vlan 30` command, the VLAN does not exist, and without adding it to the allowed list, the trunk will drop any frames tagged with VLAN 30. On the ENCOR 350-401 exam, this question tests your understanding of the two-step requirement for trunking new VLANs—creation and permission—and often appears as a common trap where candidates assume simply adding a VLAN to the allowed list is sufficient. A key memory tip is “Create then Permit”: first create the VLAN globally, then use `switchport trunk allowed vlan add 30` to include it on the trunk.
350-401 SD-Access Architecture Practice Question
This 350-401 practice question tests your understanding of sd-access architecture. 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.
Consider this VLAN configuration on a Cisco switch:
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VLAN 30 must be created and added to the allowed VLAN list on the trunk.
Option A is correct because a trunk port only forwards traffic for VLANs that exist in the switch's VLAN database and are explicitly permitted in the allowed VLAN list. VLAN 30 is neither created (no 'vlan 30' command) nor added to the trunk's allowed list (missing 'switchport trunk allowed vlan add 30'), so the switch will drop any frames tagged with VLAN 30. Creating the VLAN and updating the allowed list ensures the trunk can forward VLAN 30 traffic.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
VLAN 30 must be created and added to the allowed VLAN list on the trunk.
Why this is correct
Without VLAN 30 created and allowed on the trunk, traffic for VLAN 30 will not be forwarded.
Related concept
Read the scenario before looking for a memorised answer.
✗
The trunk must be configured as an access port for VLAN 30.
Why it's wrong here
An access port can only carry a single VLAN; a trunk is required for multiple VLANs.
✗
The native VLAN must be changed to VLAN 30.
Why it's wrong here
The native VLAN is used for untagged traffic; it does not need to be changed to carry VLAN 30.
✗
The switchport mode must be changed to dynamic desirable.
Why it's wrong here
Dynamic trunking protocols (DTP) are not required; the trunk mode is already set correctly.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that simply creating a VLAN on the switch is enough for trunk traffic, but the allowed VLAN list must also be explicitly updated, or the trunk will drop frames for that VLAN.
Detailed technical explanation
How to think about this question
Under the hood, a Cisco switch uses the VLAN database and the trunk's allowed VLAN list (stored in the VLAN Trunking Protocol (VTP) or local VLAN configuration) to filter frames. When a trunk receives a frame with a VLAN tag not in the allowed list, the switch discards it at the hardware level using the TCAM. In real-world scenarios, forgetting to add a new VLAN to the allowed list on both ends of a trunk is a common cause of connectivity issues, especially when extending a new subnet across multiple switches.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
SD-Access Architecture — This question tests SD-Access Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: VLAN 30 must be created and added to the allowed VLAN list on the trunk. — Option A is correct because a trunk port only forwards traffic for VLANs that exist in the switch's VLAN database and are explicitly permitted in the allowed VLAN list. VLAN 30 is neither created (no 'vlan 30' command) nor added to the trunk's allowed list (missing 'switchport trunk allowed vlan add 30'), so the switch will drop any frames tagged with VLAN 30. Creating the VLAN and updating the allowed list ensures the trunk can forward VLAN 30 traffic.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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