- A
Add an outbound NACL rule allowing TCP on destination ports 1024–65535 to permit response traffic to clients' ephemeral ports
Ephemeral ports are the temporary high-numbered ports clients open for receiving responses. Because NACLs are stateless, return traffic must be explicitly allowed by an outbound rule. The rule 'Allow TCP outbound to 0.0.0.0/0 on ports 1024–65535' covers all client ephemeral port ranges and allows the web server's responses to flow back to the client.
- B
Enable stateful packet inspection on the NACL by toggling the 'track connections' setting in the VPC console
Why wrong: NACLs are always stateless and there is no setting to enable stateful inspection. Stateful packet filtering is a feature of security groups, not NACLs. The NACL always requires explicit inbound and outbound rules for both request and response traffic.
- C
Add a security group outbound rule allowing all traffic because NACL rules only apply to inbound traffic
Why wrong: NACLs apply to both inbound and outbound traffic on the subnet. Security group outbound rules are separate from NACL outbound rules. The security group may already allow outbound traffic, but the NACL is a separate layer that also must permit the outbound response packets.
- D
Change port 443 to allow both TCP and UDP protocols in the inbound NACL rule
Why wrong: HTTPS uses TCP only. Changing to UDP would not match HTTPS connections. The problem is not the protocol on the inbound rule — it is the missing outbound rule for ephemeral ports on the response side.
SOA-C02 Practice Question: NACL ephemeral port rules required for response…
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: 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 security team applied Network ACL rules to a subnet to allow inbound TCP traffic on port 443 (HTTPS). Users connecting from the internet can initiate connections, but they never receive responses. The NACL is applied to the subnet containing the web servers. What is missing?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"never"Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
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
Add an outbound NACL rule allowing TCP on destination ports 1024–65535 to permit response traffic to clients' ephemeral ports
Network ACLs are stateless, meaning they evaluate each packet independently without tracking connection state. While the inbound rule allows HTTPS traffic (TCP 443) to reach the web servers, the outbound response traffic from the servers to the clients' ephemeral ports (typically 1024–65535) is blocked by the default deny-all outbound rule. Adding an outbound NACL rule allowing TCP traffic on destination ports 1024–65535 permits the response traffic to flow back to the clients, resolving the issue.
Key principle: 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.
- ✓
Add an outbound NACL rule allowing TCP on destination ports 1024–65535 to permit response traffic to clients' ephemeral ports
Why this is correct
Ephemeral ports are the temporary high-numbered ports clients open for receiving responses. Because NACLs are stateless, return traffic must be explicitly allowed by an outbound rule. The rule 'Allow TCP outbound to 0.0.0.0/0 on ports 1024–65535' covers all client ephemeral port ranges and allows the web server's responses to flow back to the client.
Clue confirmation
The clue word "never" in the question point toward this answer.
Related concept
NACL
- ✗
Enable stateful packet inspection on the NACL by toggling the 'track connections' setting in the VPC console
Why it's wrong here
NACLs are always stateless and there is no setting to enable stateful inspection. Stateful packet filtering is a feature of security groups, not NACLs. The NACL always requires explicit inbound and outbound rules for both request and response traffic.
- ✗
Add a security group outbound rule allowing all traffic because NACL rules only apply to inbound traffic
Why it's wrong here
NACLs apply to both inbound and outbound traffic on the subnet. Security group outbound rules are separate from NACL outbound rules. The security group may already allow outbound traffic, but the NACL is a separate layer that also must permit the outbound response packets.
- ✗
Change port 443 to allow both TCP and UDP protocols in the inbound NACL rule
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse stateless NACLs with stateful security groups, assuming that allowing inbound traffic automatically permits outbound responses, when in fact NACLs require explicit outbound rules for return traffic.
Detailed technical explanation
How to think about this question
Network ACLs operate at the subnet level and evaluate rules in order by rule number, with a default deny-all rule at the end. When a client initiates a connection from an ephemeral port (e.g., 34567) to the server's port 443, the server responds to that same ephemeral port; without an explicit outbound NACL rule allowing the response, the packet is dropped. This stateless behavior contrasts with security groups, which automatically allow return traffic for established connections, making NACL configuration more error-prone in scenarios with dynamic client ports.
KKey Concepts to Remember
- NACL
- ephemeral ports
- stateless
- inbound and outbound rules
- 1024-65535
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
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 nACL, then practise related SOA-C02 questions on the same topic to reinforce the concept.
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Networking and Content Delivery — study guide chapter
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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 — NACL.
What is the correct answer to this question?
The correct answer is: Add an outbound NACL rule allowing TCP on destination ports 1024–65535 to permit response traffic to clients' ephemeral ports — Network ACLs are stateless, meaning they evaluate each packet independently without tracking connection state. While the inbound rule allows HTTPS traffic (TCP 443) to reach the web servers, the outbound response traffic from the servers to the clients' ephemeral ports (typically 1024–65535) is blocked by the default deny-all outbound rule. Adding an outbound NACL rule allowing TCP traffic on destination ports 1024–65535 permits the response traffic to flow back to the clients, resolving the issue.
What should I do if I get this SOA-C02 question wrong?
Review nACL, then practise related SOA-C02 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "never". Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
What is the key concept behind this question?
NACL
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Last reviewed: Jun 11, 2026
This SOA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SOA-C02 exam.
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