- A
NACLs are stateless, so you must update the NACL to allow the return (outbound) ephemeral port range; security groups alone cannot override a blocked NACL.
Stateless NACLs require both inbound and outbound rules. Missing outbound for ephemeral ports will block return traffic even if SG rules are correct.
- B
NACLs are stateful and automatically track connections; the fix is to add a new inbound rule to the security group for client source ports.
Why wrong: NACLs are stateless; connection tracking occurs at the security group level only. Adding SG inbound rules won’t unblock outbound traffic blocked by the NACL.
- C
The issue is caused by ALB health checks; configure a new target group health check on port 80 so traffic can be routed.
Why wrong: Health checks may affect routing, but the symptom points to NACL blocking return packets. Changing health check ports won’t address NACL stateless behavior.
- D
Because instances are in private subnets, add a NAT gateway so return traffic can reach the internet over dynamic routing.
Why wrong: NAT affects internet egress, not east-west return paths inside the VPC subnet. The observed NACL rule gap is within the subnet path.
SAA-C03 Design Secure Architectures Practice Question
This SAA-C03 practice question tests your understanding of design secure architectures. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: nACLs are stateless, requiring explicit rules for both inbound and outbound traffic.. 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.
An application runs on EC2 instances in private subnets behind an Application Load Balancer (ALB). Security groups allow inbound HTTPS (443) from the ALB’s security group to the instance security group, and outbound from instances is set to allow ephemeral ports.
Despite this, clients see connection timeouts. After reviewing network ACLs, you find the NACL associated with the instance subnet has an inbound allow for destination port 443, but it does not have a corresponding outbound allow for ephemeral ports.
What is the most likely reason the traffic fails, and what should be updated?
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
NACLs are stateless, so you must update the NACL to allow the return (outbound) ephemeral port range; security groups alone cannot override a blocked NACL.
Network ACLs are stateless, meaning they do not automatically allow return traffic. Even though the security group allows inbound HTTPS from the ALB, the NACL blocks the return traffic because it lacks an outbound rule for ephemeral ports (typically 1024-65535). Since NACLs are evaluated before security groups, a missing outbound allow rule causes the response packets to be dropped, resulting in connection timeouts.
Key principle: NACLs are stateless, requiring explicit rules for both inbound and outbound traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
NACLs are stateless, so you must update the NACL to allow the return (outbound) ephemeral port range; security groups alone cannot override a blocked NACL.
Why this is correct
Stateless NACLs require both inbound and outbound rules. Missing outbound for ephemeral ports will block return traffic even if SG rules are correct.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
NACLs are stateless, requiring explicit rules for both inbound and outbound traffic.
- ✗
NACLs are stateful and automatically track connections; the fix is to add a new inbound rule to the security group for client source ports.
Why it's wrong here
NACLs are stateless; connection tracking occurs at the security group level only. Adding SG inbound rules won’t unblock outbound traffic blocked by the NACL.
- ✗
The issue is caused by ALB health checks; configure a new target group health check on port 80 so traffic can be routed.
Why it's wrong here
Health checks may affect routing, but the symptom points to NACL blocking return packets. Changing health check ports won’t address NACL stateless behavior.
- ✗
Because instances are in private subnets, add a NAT gateway so return traffic can reach the internet over dynamic routing.
Why it's wrong here
NAT affects internet egress, not east-west return paths inside the VPC subnet. The observed NACL rule gap is within the subnet path.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume security groups' stateful nature applies to NACLs, or they confuse the direction of the missing rule (inbound vs. outbound) and overlook the need for an outbound ephemeral port rule in the NACL.
Detailed technical explanation
How to think about this question
NACLs operate at the subnet level and are evaluated in numeric order; they are stateless, so each direction of traffic (request and response) must be explicitly allowed. Ephemeral ports (1024-65535) are used by the client to receive the server's response; without an outbound allow rule for these ports, the response packets are silently dropped. In contrast, security groups are stateful and automatically allow return traffic, but they cannot override a blocked NACL because NACLs are evaluated first.
KKey Concepts to Remember
- NACLs are stateless, requiring explicit rules for both inbound and outbound traffic.
- NACLs process rules in order, from lowest to highest, and stop at the first match.
- NACLs operate at the subnet level, applying to all instances within that subnet.
- Ephemeral ports (1024-65535) are used for return traffic by clients and servers.
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
NACLs are stateless, requiring explicit rules for both inbound and outbound traffic.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review nACLs are stateless, requiring explicit rules for both inbound and outbound traffic., then practise related SAA-C03 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Secure Architectures — This question tests Design Secure Architectures — NACLs are stateless, requiring explicit rules for both inbound and outbound traffic..
What is the correct answer to this question?
The correct answer is: NACLs are stateless, so you must update the NACL to allow the return (outbound) ephemeral port range; security groups alone cannot override a blocked NACL. — Network ACLs are stateless, meaning they do not automatically allow return traffic. Even though the security group allows inbound HTTPS from the ALB, the NACL blocks the return traffic because it lacks an outbound rule for ephemeral ports (typically 1024-65535). Since NACLs are evaluated before security groups, a missing outbound allow rule causes the response packets to be dropped, resulting in connection timeouts.
What should I do if I get this SAA-C03 question wrong?
Review nACLs are stateless, requiring explicit rules for both inbound and outbound traffic., then practise related SAA-C03 questions on the same topic to reinforce the concept.
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?
NACLs are stateless, requiring explicit rules for both inbound and outbound traffic.
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Last reviewed: Jun 11, 2026
This SAA-C03 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 SAA-C03 exam.
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