- A
The subnet’s network ACL is blocking outbound ephemeral ports.
Correct. The network ACL is stateless and must allow inbound ephemeral ports for return traffic. If it blocks them, the connection fails.
- B
The NAT Gateway does not have an Elastic IP.
Why wrong: Incorrect. The scenario states the NAT Gateway has an Elastic IP.
- C
The private subnet has a route to an internet gateway.
Why wrong: Incorrect. A private subnet should not have a route to an IGW; that would make it public.
- D
The security group is blocking inbound traffic from the NAT Gateway.
Why wrong: Incorrect. Security groups are stateful, so inbound traffic from the NAT Gateway is automatically allowed if outbound HTTPS is allowed.
Question 1,016 of 1,546
SOA-C02 Network ACL (NACL) Practice Question
This SOA-C02 practice question tests your understanding of networking and content delivery. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: network ACL (NACL). 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 SysOps administrator is troubleshooting an issue where an EC2 instance in a private subnet cannot connect to the internet. The instance has a security group allowing outbound HTTPS traffic. The subnet’s route table has a default route (0.0.0.0/0) to a NAT Gateway. The NAT Gateway is in a public subnet with an Elastic IP and a route to an internet gateway. What is a likely cause of the issue?
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
✓
The subnet’s network ACL is blocking outbound ephemeral ports.
The correct answer is A. Network ACLs are stateless, so even if outbound HTTPS (port 443) is allowed, the NACL must also allow inbound ephemeral ports (1024-65535) for the return traffic. If a custom NACL is blocking those inbound ports, the connection fails, even though the security group (stateful) automatically allows return traffic. Option B is incorrect because the NAT Gateway does have an Elastic IP. Option C is incorrect because a private subnet should not have a direct route to an IGW. Option D is incorrect because security groups are stateful and do not block inbound traffic from the NAT Gateway if outbound is allowed.
Key principle: Network ACL (NACL)
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 subnet’s network ACL is blocking outbound ephemeral ports.
- ✗
The NAT Gateway does not have an Elastic IP.
- ✗
The private subnet has a route to an internet gateway.
Why it's wrong here
Incorrect. A private subnet should not have a route to an IGW; that would make it public.
- ✗
The security group is blocking inbound traffic from the NAT Gateway.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Scenario analysis trap
Incorrect. The scenario states the NAT Gateway has an Elastic IP.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Network ACL (NACL)
- Security Group
- Ephemeral Ports
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
Network ACL (NACL)
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review network ACL (NACL), then practise related SOA-C02 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
Networking and Content Delivery — This question tests Networking and Content Delivery — Network ACL (NACL).
What is the correct answer to this question?
The correct answer is: The subnet’s network ACL is blocking outbound ephemeral ports. — The correct answer is A. Network ACLs are stateless, so even if outbound HTTPS (port 443) is allowed, the NACL must also allow inbound ephemeral ports (1024-65535) for the return traffic. If a custom NACL is blocking those inbound ports, the connection fails, even though the security group (stateful) automatically allows return traffic. Option B is incorrect because the NAT Gateway does have an Elastic IP. Option C is incorrect because a private subnet should not have a direct route to an IGW. Option D is incorrect because security groups are stateful and do not block inbound traffic from the NAT Gateway if outbound is allowed.
What should I do if I get this SOA-C02 question wrong?
Review network ACL (NACL), then practise related SOA-C02 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Network ACL (NACL)
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Last reviewed: Jun 20, 2026
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