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SOA-C02 Practice Question: NACL ephemeral port rules required for response…
This SOA-C02 practice question tests your understanding of nacl ephemeral port rules required for response…. 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?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
Enable stateful packet inspection on the NACL by toggling the 'track connections' setting in the VPC console
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.
B
Distractor review
Add a security group outbound rule allowing all traffic because NACL rules only apply to inbound traffic
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.
C
Distractor review
Change port 443 to allow both TCP and UDP protocols in the inbound NACL rule
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.
D
Best answer
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.
Common exam trap
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.
Technical deep dive
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
- 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
Related practice questions
Related SOA-C02 practice-question pages
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A company uses Amazon CloudFront to deliver content to a global audience. The origin is an Application Load Balancer in us-east-1. The SysOps administrator wants to reduce costs by minimizing the number of requests that reach the origin server. Which action should the administrator take?
Question 2
A company runs a batch processing application on Amazon EC2 that runs for 2 hours every night. The workload can tolerate interruptions. Which EC2 purchasing option provides the lowest cost for this use case?
Question 3
A SysOps administrator needs to monitor the CPU utilization of an Amazon RDS DB instance and receive an alarm when CPU utilization exceeds 80% for 5 consecutive minutes. Which AWS service should be used to create this alarm?
Question 4
A company runs a critical web application on Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer (ALB). The application uses session stickiness (sticky sessions) to maintain user sessions. The SysOps administrator notices that when instances are replaced during a scale-in or failure event, users lose their session data. The administrator needs to preserve session data across instance failures without losing stickiness benefits. What should the administrator do?
Question 5
A company runs a production web application on a single Amazon EC2 instance. The application experiences a predictable and steady workload 24/7. The SysOps administrator wants to minimize compute costs for this instance while ensuring it remains available during the expected workload. Which EC2 purchasing option should the administrator use?
Question 6
A company has a VPC with public and private subnets. The private subnets host application servers that need to make outbound HTTPS connections to the internet. The SysOps administrator must implement a solution that provides outbound internet connectivity while preventing inbound connections from the internet. Additionally, the solution must allow the company to control which domains the application servers can access. Which solution should the administrator implement?
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
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 — Unlike security groups, NACLs are stateless — they evaluate inbound and outbound traffic independently without tracking connection state. When a client connects on port 443, the server responds using the client's ephemeral source port (typically in the range 1024–65535 on Linux, or 49152–65535 on Windows). If the NACL does not have an outbound rule allowing TCP traffic on the ephemeral port range (1024–65535), the response packets are blocked at the NACL, and the client receives no data. Adding an outbound rule allowing TCP destination ports 1024–65535 (or the full range 0–65535) resolves 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.
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