- A
Allow VLAN 20 on the trunk
By default, some trunks may carry only VLAN 1 unless explicitly configured. Adding VLAN 20 to the allowed VLAN list on the trunk ensures that traffic from VLAN 20 can traverse the link.
- B
Set the native VLAN to 20 on both switches
Why wrong: The native VLAN is used for untagged traffic on the trunk. Changing it to 20 would not help carry tagged VLAN 20 traffic; it might cause miscommunication if the native VLANs do not match.
- C
Configure the trunk port as an access port in VLAN 20
Why wrong: An access port belongs to a single VLAN and does not use tagging. To carry multiple VLANs, a trunk (tagged) port is required.
- D
Enable VLAN pruning for all VLANs on the trunk
Why wrong: VLAN pruning (e.g., VTP pruning) removes unnecessary VLAN traffic from trunks but does not actually permit a VLAN to be carried; the VLAN must still be allowed on the trunk.
Quick Answer
The answer is to allow VLAN 20 on the trunk link. This is correct because a trunk port carries traffic for multiple VLANs using 802.1Q tagging, and while all VLANs are permitted by default, any VLAN not explicitly allowed will have its frames dropped at the trunk interface. By configuring “switchport trunk allowed vlan 20” on both ends of the link, you ensure that the tagged frames from the finance workstations in VLAN 20 can traverse the trunk to reach the finance server on the other switch. On the CompTIA Network+ N10-009 exam, this tests your understanding of VLAN pruning and trunk configuration—a common trap is assuming that simply creating a VLAN on a switch automatically allows it across a trunk. Remember the memory tip: “If it’s not allowed, it’s not loud”—a VLAN must be explicitly permitted on a trunk to send its traffic across the link.
N10-009 Network Implementation Practice Question
This N10-009 practice question tests your understanding of network implementation. 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 implementing VLANs for a company. The finance department's workstations are connected to switch ports configured as access ports in VLAN 20. The finance server is located in a different building and is connected to a second switch. The two switches are interconnected via a trunk link. What must be configured on the trunk link to allow finance workstations to communicate with the finance server?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Allow VLAN 20 on the trunk
A trunk link carries traffic for multiple VLANs. By default, all VLANs are allowed on a trunk, but if VLAN 20 is not explicitly permitted, its traffic will be dropped. Configuring 'switchport trunk allowed vlan 20' on both ends ensures that frames tagged with VLAN 20 traverse the trunk, enabling communication between the finance workstations (access ports in VLAN 20) and the finance server.
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.
- ✓
Allow VLAN 20 on the trunk
- ✗
Set the native VLAN to 20 on both switches
Why it's wrong here
The native VLAN is used for untagged traffic on the trunk. Changing it to 20 would not help carry tagged VLAN 20 traffic; it might cause miscommunication if the native VLANs do not match.
- ✗
Configure the trunk port as an access port in VLAN 20
Why it's wrong here
An access port belongs to a single VLAN and does not use tagging. To carry multiple VLANs, a trunk (tagged) port is required.
- ✗
Enable VLAN pruning for all VLANs on the trunk
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that simply creating a VLAN and assigning access ports is enough for inter-switch communication, when in fact the trunk must explicitly permit that VLAN in its allowed list.
Detailed technical explanation
How to think about this question
IEEE 802.1Q trunking inserts a 4-byte tag into Ethernet frames to identify the VLAN. The 'switchport trunk allowed vlan' command creates an ACL-like filter on the trunk interface; if VLAN 20 is not in the allowed list, the switch discards those frames at the hardware level. In a real-world scenario, forgetting to add a new VLAN to the trunk is a common cause of 'same VLAN, no connectivity' issues, even when access ports and the server are correctly configured.
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.
What to study next
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FAQ
Questions learners often ask
What does this N10-009 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Allow VLAN 20 on the trunk — A trunk link carries traffic for multiple VLANs. By default, all VLANs are allowed on a trunk, but if VLAN 20 is not explicitly permitted, its traffic will be dropped. Configuring 'switchport trunk allowed vlan 20' on both ends ensures that frames tagged with VLAN 20 traverse the trunk, enabling communication between the finance workstations (access ports in VLAN 20) and the finance server.
What should I do if I get this N10-009 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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Last reviewed: Jun 11, 2026
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.
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