- A
DNS resolution failure
Why wrong: DNS failure would prevent resolving hostnames, but the user could still access external websites by IP address. The scenario describes general external access failure, not just name resolution.
- B
Incorrect default gateway
Why wrong: If the default gateway were incorrect, the user would not be able to access the default gateway itself, nor internal servers on different subnets. The user can access internal servers, so the gateway is correct.
- C
NAT configuration issue
NAT is required to translate private addresses to a public address for internet access. If NAT is not configured or malfunctioning, outbound traffic will not reach the internet even if the ACL permits it.
- D
Proxy server misconfiguration
Why wrong: A misconfigured proxy could block internet access, but the question states the ACL permits all outbound traffic. Proxy issues are possible but less likely than NAT, and the scenario does not mention proxy settings.
Quick Answer
The answer is a NAT configuration issue. This is correct because the user can reach internal servers and the default gateway, proving Layer 3 connectivity and routing are working locally, while the ACL permits all outbound traffic, ruling out a firewall block. The failure to reach external websites points directly to a missing or incorrect Network Address Translation (NAT) rule, such as Port Address Translation (PAT) on the router’s outside interface, which is required to translate private IP addresses into a public IP for internet access. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to isolate NAT misconfiguration as a distinct cause of internet access failure, often appearing as a distractor where students mistakenly blame ACLs or routing. A common trap is assuming any external connectivity issue is a firewall problem, but remember: if internal resources work and outbound ACLs are permissive, the bottleneck is almost always NAT. Memory tip: “Internal fine, external blind? Check NAT’s behind.”
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 reports they can access internal servers and the default gateway but cannot reach external websites. The technician checks the router's ACL and finds a rule that permits all outbound traffic. 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.
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
NAT configuration issue
The user can access internal servers and the default gateway, indicating Layer 3 connectivity within the local network. However, external websites are unreachable. Since the ACL permits all outbound traffic, the issue is not a blocked outbound rule. The most likely cause is a NAT configuration issue, such as missing or incorrect IP masquerading (PAT) on the router's outside interface, which prevents internal private IP addresses from being translated to a public IP address for internet access.
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.
- ✗
DNS resolution failure
Why it's wrong here
DNS failure would prevent resolving hostnames, but the user could still access external websites by IP address. The scenario describes general external access failure, not just name resolution.
- ✗
Incorrect default gateway
Why it's wrong here
If the default gateway were incorrect, the user would not be able to access the default gateway itself, nor internal servers on different subnets. The user can access internal servers, so the gateway is correct.
- ✓
NAT configuration issue
Why this is correct
NAT is required to translate private addresses to a public address for internet access. If NAT is not configured or malfunctioning, outbound traffic will not reach the internet even if the ACL permits it.
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.
- ✗
Proxy server misconfiguration
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the misconception that an ACL permitting all outbound traffic guarantees internet access, when in fact NAT must be properly configured to translate private IP addresses to a routable public IP address for external reachability.
Trap categories for this question
Scenario analysis trap
DNS failure would prevent resolving hostnames, but the user could still access external websites by IP address. The scenario describes general external access failure, not just name resolution.
Detailed technical explanation
How to think about this question
NAT (Network Address Translation) is typically configured using the 'ip nat inside' and 'ip nat outside' interface commands, along with an access list defining which internal addresses to translate. A common misconfiguration is forgetting to apply the 'ip nat inside source list <acl> interface <outside> overload' command, which enables PAT (Port Address Translation) to map multiple private addresses to a single public IP. In real-world scenarios, a technician might verify NAT with 'show ip nat translations' and 'debug ip nat' to see if translations are being created for outbound traffic.
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.
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.
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Network Troubleshooting — study guide chapter
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FAQ
Questions learners often ask
What does this N10-009 question test?
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: NAT configuration issue — The user can access internal servers and the default gateway, indicating Layer 3 connectivity within the local network. However, external websites are unreachable. Since the ACL permits all outbound traffic, the issue is not a blocked outbound rule. The most likely cause is a NAT configuration issue, such as missing or incorrect IP masquerading (PAT) on the router's outside interface, which prevents internal private IP addresses from being translated to a public IP address for internet access.
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 →
Same concept, more angles
1 more ways this is tested on N10-009
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network technician is troubleshooting an issue where users on VLAN 20 can access internal servers and the default gateway but cannot reach any external websites. The router's ACL is configured to permit all outbound traffic. What is the most likely cause of this issue?
medium- A.The DNS server is unreachable from the VLAN
- B.The DHCP server is not providing a default gateway
- ✓ C.NAT is not configured or is misconfigured on the router
- D.The switch port for the router is in the wrong VLAN
Why C: Since users can access internal servers and the default gateway, Layer 3 connectivity within the VLAN is working, and the router's ACL permits all outbound traffic. The inability to reach external websites while internal resources are reachable strongly indicates that Network Address Translation (NAT) is either not configured or misconfigured on the router. Without NAT, private IP addresses from VLAN 20 cannot be translated to a public IP, so return traffic from external web servers has no route back to the internal hosts.
Keep practising
More N10-009 practice questions
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- Which of the following is a characteristic of a Layer 2 network switch?
- Which of the following network devices operates primarily at Layer 2 of the OSI model and uses MAC addresses to forward…
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Last reviewed: Jun 30, 2026
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