- A
The router is not configured with a routing protocol.
Why wrong: A routing protocol is unnecessary for directly connected networks; the router automatically knows about them.
- B
IP routing is disabled on the router.
If IP routing is disabled, the router will not forward packets between its interfaces, preventing inter-subnet communication.
- C
The hosts in subnet A have the wrong default gateway.
Why wrong: The hosts can ping the router interface, so the default gateway is correctly set to 10.0.1.1.
- D
The switch in subnet A is blocking ICMP traffic.
Why wrong: Switches forward ICMP at Layer 2; blocking would require an ACL, which is unlikely in this scenario.
Question 188 of 520
N10-009 Networking Concepts Practice Question
This N10-009 practice question tests your understanding of networking concepts. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 technician is configuring a small office network with two subnets: 10.0.1.0/24 and 10.0.2.0/24. Each subnet has its own switch, and both switches are connected to a router with interfaces 10.0.1.1 and 10.0.2.1. Hosts on subnet A can ping the router's interface in their subnet but cannot ping hosts on subnet B. Which of the following is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
✓
IP routing is disabled on the router.
The hosts on subnet A can ping their default gateway (10.0.1.1) but cannot reach hosts on subnet B, which indicates that the router is not forwarding packets between the two directly connected subnets. This behavior is characteristic of a router with IP routing disabled, as the router will not perform inter-VLAN or inter-subnet forwarding unless the 'ip routing' command is enabled globally. Without IP routing, the router acts as a host and will only respond to traffic destined for its own interfaces, dropping any packets that require forwarding to another subnet.
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 router is not configured with a routing protocol.
Why it's wrong here
A routing protocol is unnecessary for directly connected networks; the router automatically knows about them.
When this WOULD be correct
In a scenario where the router does not have directly connected interfaces to both subnets (e.g., subnets are behind other routers), and the router needs to dynamically learn routes to reach them, then a routing protocol would be necessary for inter-subnet communication.
- ✓
IP routing is disabled on the router.
Why this is correct
If IP routing is disabled, the router will not forward packets between its interfaces, preventing inter-subnet communication.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The hosts in subnet A have the wrong default gateway.
Why it's wrong here
The hosts can ping the router interface, so the default gateway is correctly set to 10.0.1.1.
When this WOULD be correct
In a scenario where hosts on subnet A cannot ping the router's interface (10.0.1.1) but can ping other hosts on the same subnet, the most likely cause would be an incorrect default gateway configured on the hosts.
- ✗
The switch in subnet A is blocking ICMP traffic.
Why it's wrong here
Switches forward ICMP at Layer 2; blocking would require an ACL, which is unlikely in this scenario.
When this WOULD be correct
In a scenario where hosts on the same subnet cannot ping each other or the local gateway, and the switch is configured with ACLs or port security that blocks ICMP, then the switch blocking ICMP would be the likely cause.
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.
✓IP routing is disabled on the router.Correct answer▾
Why this is correct
If IP routing is disabled, the router will not forward packets between its interfaces, preventing inter-subnet communication.
✗The router is not configured with a routing protocol.Wrong answer — click to see why▾
Why this is wrong here
The router is directly connected to both subnets (10.0.1.0/24 and 10.0.2.0/24), so it automatically has routes to these networks. A routing protocol is only needed to learn routes to non-directly connected networks, which is not the case here.
★ When this WOULD be the correct answer
In a scenario where the router does not have directly connected interfaces to both subnets (e.g., subnets are behind other routers), and the router needs to dynamically learn routes to reach them, then a routing protocol would be necessary for inter-subnet communication.
Why candidates choose this
Candidates often assume that any routing between subnets requires a routing protocol, not realizing that directly connected routes are automatically added and sufficient for communication between directly attached networks.
✗The hosts in subnet A have the wrong default gateway.Wrong answer — click to see why▾
Why this is wrong here
The hosts can ping the router's interface in their subnet, indicating the default gateway is correctly configured. The issue is inter-subnet routing, not the gateway address.
★ When this WOULD be the correct answer
In a scenario where hosts on subnet A cannot ping the router's interface (10.0.1.1) but can ping other hosts on the same subnet, the most likely cause would be an incorrect default gateway configured on the hosts.
Why candidates choose this
Candidates often assume that connectivity issues between subnets stem from incorrect gateway settings, overlooking that the router's routing capability (IP routing enabled) is required for forwarding between subnets.
✗The switch in subnet A is blocking ICMP traffic.Wrong answer — click to see why▾
Why this is wrong here
The switch in subnet A is a Layer 2 device and does not block ICMP traffic between subnets; inter-subnet communication requires a router, and the issue is that the router is not forwarding packets because IP routing is disabled.
★ When this WOULD be the correct answer
In a scenario where hosts on the same subnet cannot ping each other or the local gateway, and the switch is configured with ACLs or port security that blocks ICMP, then the switch blocking ICMP would be the likely cause.
Why candidates choose this
Candidates may think switches can filter traffic between subnets or that ICMP blocking is a common issue, but switches operate at Layer 2 and do not route between subnets.
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 N10-009 exam often tests the distinction between 'routing protocol' and 'IP routing' — candidates mistakenly think a routing protocol is required for directly connected subnets, when in fact the 'ip routing' global command is the fundamental enabler of any Layer 3 forwarding.
Trap categories for this question
Scenario analysis trap
Switches forward ICMP at Layer 2; blocking would require an ACL, which is unlikely in this scenario.
Detailed technical explanation
How to think about this question
On Cisco IOS routers, IP routing is enabled by default, but if it has been explicitly disabled with the 'no ip routing' command, the router will not forward packets between its interfaces, even if they are directly connected. This is a common misconfiguration during lab exercises or when a device is repurposed from a host role. The router will still respond to pings on its own IP addresses because those are handled by the control plane, but it will drop any packet with a destination IP not matching one of its own interfaces.
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: IP routing is disabled on the router. — The hosts on subnet A can ping their default gateway (10.0.1.1) but cannot reach hosts on subnet B, which indicates that the router is not forwarding packets between the two directly connected subnets. This behavior is characteristic of a router with IP routing disabled, as the router will not perform inter-VLAN or inter-subnet forwarding unless the 'ip routing' command is enabled globally. Without IP routing, the router acts as a host and will only respond to traffic destined for its own interfaces, dropping any packets that require forwarding to another subnet.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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.