This 350-401 practice question tests your understanding of vlans and trunking. 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.
Given the following configuration on a Cisco IOS switch:
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 actively try to form a trunk and will succeed if the other side is set to trunk, desirable, or auto.
The `switchport mode dynamic desirable` command configures the interface to actively send Dynamic Trunking Protocol (DTP) frames to negotiate trunking. If the neighboring interface is set to trunk, dynamic desirable, or dynamic auto, the negotiation will succeed and the link will become a trunk. This is because dynamic desirable actively initiates the negotiation, unlike dynamic auto which only responds.
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.
✓
The interface will actively try to form a trunk and will succeed if the other side is set to trunk, desirable, or auto.
Why this is correct
Correct. Dynamic desirable sends DTP frames and can form a trunk with several modes.
Related concept
Read the scenario before looking for a memorised answer.
✗
The interface will only become a trunk if the other side is set to trunk.
Why it's wrong here
Incorrect. It can also form a trunk with desirable or auto.
✗
The interface will always remain an access port.
Why it's wrong here
Incorrect. Dynamic desirable can become a trunk if the neighbor cooperates.
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between dynamic desirable and dynamic auto, where the trap is that candidates forget dynamic desirable actively sends DTP frames and can form a trunk with dynamic auto, while dynamic auto only responds and will not form a trunk with another auto interface.
Detailed technical explanation
How to think about this question
DTP is a Cisco proprietary protocol that operates at Layer 2 and uses multicast frames (01-00-0C-CC-CC-CC) to negotiate trunking. The dynamic desirable mode sends DTP frames every 30 seconds and will form a trunk with any neighbor that is in trunk, desirable, or auto mode, but not with access mode. In real-world scenarios, using dynamic desirable can cause unexpected trunking if a misconfigured neighbor is in auto mode, potentially leading to VLAN hopping security risks.
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 actively try to form a trunk and will succeed if the other side is set to trunk, desirable, or auto. — The `switchport mode dynamic desirable` command configures the interface to actively send Dynamic Trunking Protocol (DTP) frames to negotiate trunking. If the neighboring interface is set to trunk, dynamic desirable, or dynamic auto, the negotiation will succeed and the link will become a trunk. This is because dynamic desirable actively initiates the negotiation, unlike dynamic auto which only responds.
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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