The answer is the computer’s local firewall blocking outbound ICMP. This is correct because the user can reach the local gateway but not an external IP like 8.8.8.8, while other hosts on the same subnet have no issue—this isolates the fault to the specific host, not the network or router. A local firewall configured to block outbound ICMP traffic will prevent ping replies from leaving the machine to external destinations, yet still allow local subnet communication, since ICMP is often restricted by default in stricter security policies. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to differentiate between host-level and infrastructure-level problems; a common trap is to blame the default gateway or DNS when the issue is actually the local firewall. Remember the memory tip: “Local ping fails out, but gateway works—check the host’s firewall first.”
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 user can ping the default gateway (192.168.1.1) but cannot ping the external IP address 8.8.8.8. Other users on the same subnet can ping 8.8.8.8 without issue. The user's IP configuration is correct: IP 192.168.1.10/24, default gateway 192.168.1.1, DNS 8.8.8.8. What 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.
Firewalls often block ICMP by default or may have been configured to do so. Since other users work, the problem is local to this machine.
B
The router is missing a default route to the internet
Why wrong: If the router lacked a default route, no user would be able to ping external IPs. Since others can, the router's routing is fine.
C
The DNS server is not resolving the hostname
Why wrong: The user is pinging an IP address directly (8.8.8.8), not a hostname, so DNS resolution is not required.
D
The network cable is loose or faulty
Why wrong: A cable issue would likely cause intermittent connectivity or failure to reach the gateway. Since pinging the gateway succeeds, the cable is functioning.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The computer's firewall is blocking outbound ICMP
The user can ping the default gateway (192.168.1.1) but not the external IP 8.8.8.8, while other users on the same subnet can ping 8.8.8.8 without issue. This isolates the problem to the user's specific host, not the network infrastructure. A local firewall on the user's computer blocking outbound ICMP (Internet Control Message Protocol) traffic would prevent ping to external IPs while still allowing local subnet communication, as ICMP is often restricted by default in some security policies.
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 computer's firewall is blocking outbound ICMP
Why this is correct
Firewalls often block ICMP by default or may have been configured to do so. Since other users work, the problem is local to this machine.
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 router is missing a default route to the internet
Why it's wrong here
If the router lacked a default route, no user would be able to ping external IPs. Since others can, the router's routing is fine.
✗
The DNS server is not resolving the hostname
Why it's wrong here
The user is pinging an IP address directly (8.8.8.8), not a hostname, so DNS resolution is not required.
✗
The network cable is loose or faulty
Why it's wrong here
A cable issue would likely cause intermittent connectivity or failure to reach the gateway. Since pinging the gateway succeeds, the cable is functioning.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a routing or DNS issue when the problem is host-specific, but the key clue is that other users on the same subnet succeed, pointing to a local host configuration or firewall problem rather than a network-wide fault.
Detailed technical explanation
How to think about this question
ICMP Echo Requests (ping) are Layer 3 packets that traverse the network stack; a host firewall (e.g., Windows Defender Firewall, iptables) can filter ICMP based on direction (inbound/outbound), interface, or IP address. In Windows, the 'File and Printer Sharing (Echo Request - ICMPv4-In)' rule controls inbound ICMP, but outbound ICMP is typically allowed unless explicitly blocked by a custom rule or third-party firewall. Real-world scenarios include corporate security policies that block outbound ICMP to prevent network reconnaissance or DDoS amplification attacks.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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 computer's firewall is blocking outbound ICMP — The user can ping the default gateway (192.168.1.1) but not the external IP 8.8.8.8, while other users on the same subnet can ping 8.8.8.8 without issue. This isolates the problem to the user's specific host, not the network infrastructure. A local firewall on the user's computer blocking outbound ICMP (Internet Control Message Protocol) traffic would prevent ping to external IPs while still allowing local subnet communication, as ICMP is often restricted by default in some security policies.
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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Question Discussion
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