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.
A network engineer is configuring a new Cisco Catalyst switch to connect to an existing network. The uplink to the distribution switch is configured as a trunk. The engineer wants to ensure that the trunk uses 802.1Q encapsulation and that the native VLAN is set to VLAN 100. The distribution switch is a Cisco Catalyst 3850. Which configuration should the engineer apply on the uplink interface?
Option A is correct because on modern Cisco Catalyst switches that run LAN Base or IP Base software, the default trunk encapsulation is 802.1Q, so the 'switchport trunk encapsulation dot1q' command is not required. The 'switchport mode trunk' forces the interface into trunking mode, and 'switchport trunk native vlan 100' sets the native VLAN to 100, which matches the requirement.
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.
Incorrect because this command restricts allowed VLANs to only VLAN 100, and does not set the native VLAN.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the fact that on modern switches (like the 3850), the 'switchport trunk encapsulation dot1q' command is not available because 802.1Q is the only supported encapsulation, leading candidates to incorrectly include it.
Trap categories for this question
Command / output trap
Incorrect because the encapsulation command is not needed on most modern switches and may be rejected.
Detailed technical explanation
How to think about this question
Under the hood, the native VLAN on an 802.1Q trunk is the VLAN that carries untagged frames; all other VLANs are tagged. Setting the native VLAN to 100 ensures that traffic from VLAN 100 is sent without an 802.1Q tag, which is critical for interoperability with devices that do not understand tagging. In a real-world scenario, if the native VLAN mismatches between two ends of a trunk, it can cause VLAN leakage or connectivity issues, making this configuration essential for proper operation.
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.
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: switchport mode trunk; switchport trunk native vlan 100 — Option A is correct because on modern Cisco Catalyst switches that run LAN Base or IP Base software, the default trunk encapsulation is 802.1Q, so the 'switchport trunk encapsulation dot1q' command is not required. The 'switchport mode trunk' forces the interface into trunking mode, and 'switchport trunk native vlan 100' sets the native VLAN to 100, which matches the requirement.
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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