Quick Answer
The answer is VLAN 99. This is correct because the switchport trunk native vlan 99 command designates VLAN 99 as the native VLAN for that trunk port, and by definition, any untagged frame received on a trunk port is automatically assigned to the native VLAN. On the Cisco DevNet Associate 200-901 exam, this concept tests your understanding of trunk port behavior and the critical distinction between tagged and untagged traffic, often appearing in configuration or troubleshooting scenarios. A common trap is assuming an untagged frame is dropped or placed into VLAN 1 by default, but the native VLAN can be changed, as shown here. Remember the key rule: on a trunk, untagged frames always go to the native VLAN, regardless of the default. A helpful memory tip is “Untagged = Native,” so if you see a trunk port without a native VLAN command, the frame defaults to VLAN 1, but when explicitly set, it follows the configured value.
This 200-901 practice question tests your understanding of network fundamentals. 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.
Refer to the exhibit. ``` interface GigabitEthernet0/1 switchport mode trunk switchport trunk native vlan 99 switchport trunk allowed vlan 10,20,30 ```
An engineer configures a trunk port as shown. A device connected to this port sends an untagged frame. Which VLAN will the switch associate the frame with?
Refer to the exhibit. ``` interface GigabitEthernet0/1 switchport mode trunk switchport trunk native vlan 99 switchport trunk allowed vlan 10,20,30 ```
VLAN 1
Why wrong: Native VLAN is configured as 99.
The frame is dropped
Why wrong: Untagged frames are accepted on trunk.
VLAN 10
Why wrong: Only tagged frames use allowed VLANs.
VLAN 99
Untagged frames are placed in native VLAN.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
VLAN 99
The switchport trunk native vlan 99 command configures VLAN 99 as the native VLAN for the trunk port. When an untagged frame arrives on a trunk port, the switch associates it with the native VLAN. Therefore, the frame is placed into VLAN 99.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
VLAN 1
Why it's wrong here
Native VLAN is configured as 99.
The frame is dropped
Why it's wrong here
Untagged frames are accepted on trunk.
VLAN 10
Why it's wrong here
Only tagged frames use allowed VLANs.
VLAN 99
Why this is correct
Untagged frames are placed in native VLAN.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Cisco often tests the misconception that untagged frames on a trunk are dropped or that the native VLAN is always VLAN 1, leading candidates to overlook the explicit native VLAN configuration.
Detailed technical explanation
On a Cisco trunk port, the native VLAN is the VLAN that carries untagged traffic. By default, the native VLAN is VLAN 1, but it can be changed with the switchport trunk native vlan command. This is critical for interoperability with devices that do not tag frames, such as IP phones or legacy switches, ensuring untagged frames are correctly associated with the intended VLAN.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
What to study next
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FAQ
Network Fundamentals — This question tests Network Fundamentals — Read the scenario before looking for a memorised answer..
The correct answer is: VLAN 99 — The switchport trunk native vlan 99 command configures VLAN 99 as the native VLAN for the trunk port. When an untagged frame arrives on a trunk port, the switch associates it with the native VLAN. Therefore, the frame is placed into VLAN 99.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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