The answer is that IP routing is disabled on the router, which prevents inter-subnet communication even though the router is directly connected to both subnets. When IP routing is disabled, the router behaves like a host device: it will respond to pings sent to its own interface IP addresses, but it will not forward packets between different subnets. This explains why hosts on subnet A can ping their default gateway at 10.0.1.1 but cannot reach any host on subnet B. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of the router’s fundamental role in layer 3 forwarding—a common trap is assuming that simply having multiple interfaces configured is enough to route traffic. Remember that a router must have the global `ip routing` command enabled to forward packets between subnets; without it, each interface operates in isolation. A helpful memory tip: “No ip routing, no inter-subnet routing.”
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 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.
✓
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.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
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 →
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.
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.