- A
1
Why wrong: A broadcast domain is isolated per VLAN; a single broadcast domain would mean all devices are in the same VLAN.
- B
3
Each VLAN (10, 20, 30) creates its own broadcast domain. Router subinterfaces do not combine them.
- C
4
Why wrong: There are only three VLANs, so there cannot be four broadcast domains unless there is an additional unmentioned VLAN.
- D
5
Why wrong: There is no fifth broadcast domain; the router does not create additional broadcast domains.
Question 190 of 520
N10-009 Networking Concepts Practice Question
This N10-009 practice question tests your understanding of networking concepts. 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 has a single switch with VLANs 10, 20, and 30 configured. The switch is connected to a router that has three subinterfaces, each in a different VLAN. How many broadcast domains are present?
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
✓
3
Each VLAN is a separate Layer 2 broadcast domain. With VLANs 10, 20, and 30 configured on the switch and a router using subinterfaces to route between them, there are exactly three broadcast domains — one per VLAN. Broadcasts are confined to their VLAN and do not cross VLAN boundaries without a Layer 3 device.
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.
- ✗
1
Why it's wrong here
A broadcast domain is isolated per VLAN; a single broadcast domain would mean all devices are in the same VLAN.
When this WOULD be correct
If the question described a single flat network with no VLANs (e.g., all devices on the same switch without VLAN configuration) and no router segmentation, then there would be only one broadcast domain.
- ✓
3
Why this is correct
Each VLAN (10, 20, 30) creates its own broadcast domain. Router subinterfaces do not combine them.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
4
Why it's wrong here
There are only three VLANs, so there cannot be four broadcast domains unless there is an additional unmentioned VLAN.
When this WOULD be correct
If the question stated that the switch had four VLANs (e.g., VLANs 10, 20, 30, and 40) and each was connected to a router subinterface, then there would be four broadcast domains, making option C correct.
- ✗
5
Why it's wrong here
There is no fifth broadcast domain; the router does not create additional broadcast domains.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓3Correct answer▾
Why this is correct
Each VLAN (10, 20, 30) creates its own broadcast domain. Router subinterfaces do not combine them.
✗1Wrong answer — click to see why▾
Why this is wrong here
Each VLAN creates a separate broadcast domain. With three VLANs (10, 20, 30) and a router with three subinterfaces, there are three distinct broadcast domains, not one.
★ When this WOULD be the correct answer
If the question described a single flat network with no VLANs (e.g., all devices on the same switch without VLAN configuration) and no router segmentation, then there would be only one broadcast domain.
Why candidates choose this
Candidates may mistakenly think that a single switch inherently creates one broadcast domain, ignoring that VLANs logically separate broadcast traffic.
✗4Wrong answer — click to see why▾
Why this is wrong here
Each VLAN creates its own broadcast domain, and with three VLANs (10, 20, 30) there are exactly three broadcast domains. Option C (4) is incorrect because there is no fourth broadcast domain; the router subinterfaces do not add additional broadcast domains beyond the VLANs.
★ When this WOULD be the correct answer
If the question stated that the switch had four VLANs (e.g., VLANs 10, 20, 30, and 40) and each was connected to a router subinterface, then there would be four broadcast domains, making option C correct.
Why candidates choose this
Candidates might mistakenly count the router subinterfaces as separate broadcast domains or think that the router itself adds an extra broadcast domain, leading them to choose 4 instead of 3.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often count the router subinterfaces as separate broadcast domains, not realizing that broadcast domains are strictly Layer 2 constructs and that the router only provides inter-VLAN routing without adding new broadcast domains.
Detailed technical explanation
How to think about this question
A broadcast domain is defined by the set of devices that receive a broadcast frame sent by any member. In a VLAN-based switched network, each VLAN corresponds to an isolated broadcast domain at Layer 2. The router’s subinterfaces (e.g., GigabitEthernet0/0.10, .20, .30) operate as the default gateways for each VLAN, but they do not create additional broadcast domains; they simply route traffic between the existing Layer 2 domains. In real-world deployments, misconfiguring subinterface encapsulation (e.g., 802.1Q) can cause VLAN leaks, inadvertently merging broadcast domains.
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
- →
Networking Concepts — study guide chapter
Learn the concepts, then practise the questions
- →
Networking Concepts practice questions
Targeted practice on this topic area only
- →
All N10-009 questions
520 questions across all exam domains
- →
CompTIA Network+ N10-009 study guide
Full concept coverage aligned to exam objectives
- →
N10-009 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related N10-009 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Networking Concepts practice questions
Practise N10-009 questions linked to Networking Concepts.
Network Implementation practice questions
Practise N10-009 questions linked to Network Implementation.
Network Operations practice questions
Practise N10-009 questions linked to Network Operations.
Network Security practice questions
Practise N10-009 questions linked to Network Security.
Network Troubleshooting practice questions
Practise N10-009 questions linked to Network Troubleshooting.
Network+ network fundamentals practice questions
Practise N10-009 questions linked to Network+ network fundamentals.
Practice this exam
Start a free N10-009 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this N10-009 question test?
Networking Concepts — This question tests Networking Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 3 — Each VLAN is a separate Layer 2 broadcast domain. With VLANs 10, 20, and 30 configured on the switch and a router using subinterfaces to route between them, there are exactly three broadcast domains — one per VLAN. Broadcasts are confined to their VLAN and do not cross VLAN boundaries without a Layer 3 device.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
More N10-009 practice questions
- Which of the following network devices operates primarily at Layer 2 of the OSI model and uses MAC addresses to forward…
- Which of the following is a characteristic of UDP when compared to TCP?
- Which of the following IPv6 addresses is a valid link-local address?
- Which of the following security mechanisms requires a user to authenticate before gaining access to the wired network at…
- Which of the following network protocols operates at the Transport layer of the OSI model and provides connection-orient…
- Which of the following is a characteristic of a connectionless protocol at the transport layer?
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.