- A
An internet gateway is attached to the VPC and a default route points to it.
Why wrong: Internet gateway would allow inbound, but instance is in private subnet.
- B
A VPC endpoint for S3 is configured.
Why wrong: VPC endpoint provides access to S3 only, not general internet.
- C
A NAT gateway is configured in a different availability zone.
Why wrong: NAT gateway would be visible in route table.
- D
An egress-only internet gateway is used for IPv6 traffic.
Egress-only internet gateway allows outbound IPv6 traffic without inbound.
Question 1,118 of 1,748
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 security engineer notices that an EC2 instance in a private subnet can reach the internet, even though there is no NAT gateway or instance in the route table. 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
✓
An egress-only internet gateway is used for IPv6 traffic.
An egress-only internet gateway (EIGW) allows outbound-only IPv6 traffic from instances in a private subnet to the internet, but it does not permit inbound connections initiated from the internet. Since the question states there is no NAT gateway or instance, and the instance can reach the internet, the most likely cause is that the VPC uses IPv6 and an EIGW is configured with a default route (::/0) pointing to it. This enables outbound internet access without a NAT device, matching the described scenario.
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.
- ✗
An internet gateway is attached to the VPC and a default route points to it.
Why it's wrong here
Internet gateway would allow inbound, but instance is in private subnet.
- ✗
A VPC endpoint for S3 is configured.
Why it's wrong here
VPC endpoint provides access to S3 only, not general internet.
- ✗
A NAT gateway is configured in a different availability zone.
- ✓
An egress-only internet gateway is used for IPv6 traffic.
Why this is correct
Egress-only internet gateway allows outbound IPv6 traffic without inbound.
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 assume internet access from a private subnet always requires a NAT gateway or instance, overlooking the fact that egress-only internet gateways provide outbound-only IPv6 internet access without any NAT device.
Detailed technical explanation
How to think about this question
An egress-only internet gateway is a horizontally scaled, redundant component that allows outbound IPv6 traffic from a VPC to the internet but drops any unsolicited inbound IPv6 traffic. It works only with IPv6 (using the ::/0 route) and is not compatible with IPv4. In a real-world scenario, if an organization migrates to IPv6 and configures an EIGW for private subnets, instances can reach the internet for updates or external APIs without needing a NAT gateway, but they remain protected from inbound 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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: An egress-only internet gateway is used for IPv6 traffic. — An egress-only internet gateway (EIGW) allows outbound-only IPv6 traffic from instances in a private subnet to the internet, but it does not permit inbound connections initiated from the internet. Since the question states there is no NAT gateway or instance, and the instance can reach the internet, the most likely cause is that the VPC uses IPv6 and an EIGW is configured with a default route (::/0) pointing to it. This enables outbound internet access without a NAT device, matching the described scenario.
What should I do if I get this SCS-C02 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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Last reviewed: Jul 4, 2026
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