The answer is that the instance does not have a public IPv4 address, network ACLs are blocking traffic, and the instance is stopped. These three causes directly prevent SSH connectivity even when the security group appears permissive. A public IPv4 address is required for internet-based SSH access, as private IPs are not routable from outside the VPC. Network ACLs operate at the subnet level and can silently deny inbound traffic regardless of security group rules, making them a common oversight. On the AWS Certified Developer Associate DVA-C02 exam, this question tests your ability to distinguish between stateful security groups and stateless network ACLs, and to verify that the instance is actually running—not just that it exists. A frequent trap is assuming that an IAM role or key pair affects network reachability; they do not. Remember the mnemonic “P.I.N.”—Public IP, Inbound NACL, and iNstance state—to quickly recall the three non-obvious causes of SSH unreachability.
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. 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 developer is troubleshooting an EC2 instance that is unreachable via SSH. The instance is in a public subnet with a security group that allows inbound SSH from 0.0.0.0/0. Which THREE are possible causes? (Choose 3.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The network ACL associated with the subnet is blocking inbound SSH.
Network ACLs can block traffic even if security group allows. The instance may not have a public IP. The IAM role doesn't affect SSH access. The key pair is used for authentication, not connectivity. The instance may be stopped.
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
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
The network ACL associated with the subnet is blocking inbound SSH.
Why this is correct
Network ACLs are stateless and must allow both inbound and outbound traffic.
Common exam trap: usable hosts are not the same as total addresses
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
How to think about this question
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.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
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
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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DVA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The network ACL associated with the subnet is blocking inbound SSH. — Network ACLs can block traffic even if security group allows. The instance may not have a public IP. The IAM role doesn't affect SSH access. The key pair is used for authentication, not connectivity. The instance may be stopped.
What should I do if I get this DVA-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DVA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
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 →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A developer is troubleshooting an EC2 instance that is unreachable via SSH. The instance passed the status checks, and the security group allows SSH from the developer's IP. What should the developer check next?
medium
A.The security group's outbound rules.
B.The route table for the subnet.
✓ C.The network ACL's outbound rules.
D.The instance's system log for kernel errors.
Why C: The network ACL is stateless and must allow both inbound and outbound traffic. Option B is correct: the outbound ephemeral port range must be allowed for the return traffic. Option A is wrong because the security group is stateful and allows return traffic automatically. Option C is wrong because the instance is reachable for status checks. Option D is wrong because route tables do not affect direct connectivity to the instance from the internet if it has a public IP.
Last reviewed: Jun 20, 2026
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This DVA-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 DVA-C02 exam.
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