The answer is that the interface will not form a trunk unless the neighbor is set to trunk or desirable. This is because DTP output interpretation shows the local mode as "Desirable," which means the switchport actively sends DTP frames to negotiate a trunk, but it will only succeed if the neighboring interface is in trunk (on) or desirable mode—if the neighbor is in dynamic auto or access mode, the trunk negotiation fails, leaving the link as an access port. On the ENCOR 350-401 exam, this tests your understanding of Dynamic Trunking Protocol (DTP) and the four possible switchport modes: access, dynamic auto, dynamic desirable, and trunk. A common trap is assuming "dynamic auto" will form a trunk with "desirable," but auto is passive and only responds to DTP, so it requires the neighbor to be trunk or desirable to actually negotiate. For a quick memory tip, remember "Desirable is the active asker, Auto is the passive waiter."
350-401 VLANs and Trunking Practice Question
This 350-401 practice question tests your understanding of vlans and trunking. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 runs the following command on Switch SW1:
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The interface will not form a trunk unless the neighbor is set to trunk or desirable.
The output shows DTP mode is 'Desirable' and DTP status is 'Trunking', meaning the interface is actively attempting to form a trunk. In DTP, a switchport in desirable mode will only successfully negotiate a trunk if the neighboring interface is configured as trunk (on) or desirable; if the neighbor is in access mode or dynamic auto, the trunk will not form. Therefore, option B is correct.
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.
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that 'dynamic desirable' will form a trunk with any neighbor, but the trap is that it requires the neighbor to be in trunk or desirable mode, not dynamic auto or access.
Detailed technical explanation
How to think about this question
DTP (Dynamic Trunking Protocol) operates on Cisco switches to negotiate trunk links between devices. The 'desirable' mode actively sends DTP frames to attempt trunk formation, while 'auto' mode only responds to received DTP frames. In a real-world scenario, if one switch is set to 'dynamic desirable' and the other to 'dynamic auto', a trunk will form because desirable sends frames that auto responds to; however, if both are 'auto', no trunk forms because neither sends initial DTP frames.
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 network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
VLANs and Trunking — This question tests VLANs and Trunking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The interface will not form a trunk unless the neighbor is set to trunk or desirable. — The output shows DTP mode is 'Desirable' and DTP status is 'Trunking', meaning the interface is actively attempting to form a trunk. In DTP, a switchport in desirable mode will only successfully negotiate a trunk if the neighboring interface is configured as trunk (on) or desirable; if the neighbor is in access mode or dynamic auto, the trunk will not form. Therefore, option B is correct.
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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