The answer is that the next hop router is unreachable from that router. When traceroute stops at a router and the next hop shows a timeout, it means the router successfully received the packet but could not forward it to the next router in the path, so it never sends back the ICMP Time Exceeded message for that hop. This directly indicates a routing failure at that point, not a destination issue or firewall block. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of how traceroute uses ICMP TTL expiration to map each hop; a common trap is assuming the destination is down or that ICMP is simply blocked, but the key clue is that the timeout occurs at a specific intermediate router, not at the final destination. Remember the memory tip: “Stops at a hop, not the top” — if the trace halts mid-path, the next hop is unreachable, not the final host.
N10-009 Network Troubleshooting Practice Question
This N10-009 practice question tests your understanding of network troubleshooting. 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 technician is troubleshooting a user's inability to connect to a server. The technician runs 'tracert' from the user's workstation and sees that traffic stops at a particular router. The last hop shows a timeout. 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.
Why wrong: If the server were off, tracert would reach the server's subnet and then time out at the last hop, not at an intermediate router.
B
The router is blocking ICMP echo requests.
Why wrong: Blocking ICMP would cause the router to not respond, but traffic might still be forwarded; subsequent hops would appear with timeouts at that router.
C
There is a routing loop.
Why wrong: A routing loop would cause repeated hops between routers, not a single stop with timeouts.
D
The next hop router is unreachable from that router.
If the router cannot reach the next hop, it cannot forward packets further, causing tracert to hang at that router.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The next hop router is unreachable from that router.
The 'tracert' command relies on ICMP Time Exceeded messages from intermediate routers to map the path. When traffic stops at a particular router and the next hop shows a timeout, it indicates that the router cannot forward the packet to the next hop, meaning the next hop router is unreachable. This is the most direct cause because the traceroute fails to receive a response from the next hop, not because the destination is off or ICMP is blocked.
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 destination server is powered off.
Why it's wrong here
If the server were off, tracert would reach the server's subnet and then time out at the last hop, not at an intermediate router.
✗
The router is blocking ICMP echo requests.
Why it's wrong here
Blocking ICMP would cause the router to not respond, but traffic might still be forwarded; subsequent hops would appear with timeouts at that router.
✗
There is a routing loop.
Why it's wrong here
A routing loop would cause repeated hops between routers, not a single stop with timeouts.
✓
The next hop router is unreachable from that router.
Why this is correct
If the router cannot reach the next hop, it cannot forward packets further, causing tracert to hang at that router.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse a timeout caused by ICMP filtering (Option B) with a true connectivity failure, but ICMP filtering would cause timeouts at the filtering router itself, not at the next hop, and traceroute uses different ICMP types that are often permitted even when echo requests are blocked.
Detailed technical explanation
How to think about this question
Traceroute works by sending packets with incrementing TTL values; each router decrements the TTL and, when it reaches zero, sends an ICMP Time Exceeded (Type 11) message back to the source. If a router cannot forward a packet because the next hop is unreachable (e.g., due to a failed link or missing route), it will either drop the packet silently or send an ICMP Destination Unreachable (Type 3, Code 0 or 1), but the traceroute will timeout because no ICMP Time Exceeded is generated. In real-world scenarios, this often occurs due to a misconfigured static route or a down interface on the next-hop router.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Troubleshooting — This question tests Network Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The next hop router is unreachable from that router. — The 'tracert' command relies on ICMP Time Exceeded messages from intermediate routers to map the path. When traffic stops at a particular router and the next hop shows a timeout, it indicates that the router cannot forward the packet to the next hop, meaning the next hop router is unreachable. This is the most direct cause because the traceroute fails to receive a response from the next hop, not because the destination is off or ICMP is blocked.
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.
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