Quick Answer
The answer is that the NACL outbound rule is blocking return traffic. This is because Network ACLs are stateless, meaning they evaluate each packet independently without tracking connection state; while the inbound rule permits SSH traffic to reach the EC2 instance, the outbound rule must explicitly allow the response traffic back to the client on ephemeral ports. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this concept frequently appears as a trap where candidates assume that allowing inbound traffic is sufficient, forgetting that stateless NACLs require symmetric rules for both directions. A common memory tip is to remember that NACLs are “no state, no sympathy”—they don’t remember your connection, so you must write rules for both inbound and outbound flows.
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. 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 SysOps administrator is troubleshooting an issue where an EC2 instance cannot be accessed via SSH from the internet. The security group allows inbound SSH (port 22) from 0.0.0.0/0. The network ACL (NACL) for the subnet has an inbound rule allowing SSH from 0.0.0.0/0. What else could be blocking access?
The NACL inbound rule is blocking traffic.
Why wrong: NACL inbound rule allows SSH.
The internet gateway is not attached to the VPC.
Why wrong: If IGW were not attached, no internet access.
The security group rule is misconfigured.
Why wrong: Security group already allows SSH.
The NACL outbound rule is blocking return traffic.
NACL outbound must allow ephemeral ports for return traffic.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The NACL outbound rule is blocking return traffic.
Option C is correct. The NACL must also have an outbound rule to allow return traffic. NACLs are stateless, so outbound rules must be explicitly set. Option A is wrong because the security group is already correct. Option B is wrong because NACL inbound is allowed. Option D is wrong because the internet gateway allows inbound traffic.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The NACL inbound rule is blocking traffic.
Why it's wrong here
NACL inbound rule allows SSH.
The internet gateway is not attached to the VPC.
Why it's wrong here
If IGW were not attached, no internet access.
The security group rule is misconfigured.
Why it's wrong here
Security group already allows SSH.
The NACL outbound rule is blocking return traffic.
Why this is correct
NACL outbound must allow ephemeral ports for return traffic.
Related concept
CIDR notation defines the prefix length.
Common exam traps
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
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
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Networking and Content Delivery — study guide chapter
Learn the concepts, then practise the questions
Networking and Content Delivery practice questions
Targeted practice on this topic area only
All SOA-C02 questions
1,546 questions across all exam domains
AWS Certified SysOps Administrator Associate SOA-C02 study guide
Full concept coverage aligned to exam objectives
SOA-C02 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise SOA-C02 questions linked to Monitoring, Logging, and Remediation.
Practise SOA-C02 questions linked to Reliability and Business Continuity.
Practise SOA-C02 questions linked to Deployment, Provisioning, and Automation.
Practise SOA-C02 questions linked to Security and Compliance.
Practise SOA-C02 questions linked to Networking and Content Delivery.
Practise SOA-C02 questions linked to Cost and Performance Optimization.
Practise SOA-C02 questions linked to SOA-C02 fundamentals.
Practise SOA-C02 questions linked to SOA-C02 scenario.
Practise SOA-C02 questions linked to SOA-C02 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Networking and Content Delivery — This question tests Networking and Content Delivery — CIDR notation defines the prefix length..
The correct answer is: The NACL outbound rule is blocking return traffic. — Option C is correct. The NACL must also have an outbound rule to allow return traffic. NACLs are stateless, so outbound rules must be explicitly set. Option A is wrong because the security group is already correct. Option B is wrong because NACL inbound is allowed. Option D is wrong because the internet gateway allows inbound traffic.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
CIDR notation defines the prefix length.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
Last reviewed: Jun 20, 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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.