Quick Answer
The answer is a misconfigured network ACL’s outbound rules blocking traffic. Even when an EC2 instance has a public IP, sits in a public subnet with a route to an internet gateway, and its security group permits all outbound traffic, the subnet’s network ACL acts as a stateless firewall that must explicitly allow both inbound and outbound traffic. If the outbound rule is missing or set to deny, the instance cannot send packets to the internet, making this the most likely cause of an EC2 internet connectivity network ACL issue. On the AWS Certified Developer Associate DVA-C02 exam, this question tests your understanding of the layered security model: security groups are stateful and only need outbound rules for response traffic, while network ACLs are stateless and require explicit rules for both directions. A common trap is assuming a security group’s outbound allow is sufficient, but the network ACL can override it. Memory tip: “SG is stateful, NACL is stateless—check both directions for internet access.”
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 cannot connect to the internet. The instance has a public IP address and is in a public subnet with a route to an internet gateway. The security group allows all outbound traffic. What is the most likely cause?
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.
The subnet's route table does not have a route to an internet gateway.
Why wrong: It has a route.
The security group's outbound rules are too restrictive.
Why wrong: Outbound traffic is allowed.
The network ACL's outbound rules are blocking traffic.
Network ACLs are stateless and must allow both inbound and outbound.
The instance does not have a public IP address.
Why wrong: It has a public IP.
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 network ACL's outbound rules are blocking traffic.
Option D is correct because a missing or misconfigured network ACL can block traffic even if security group allows it. Option A is wrong because the instance has a public IP. Option B is wrong because the route table has a route to an internet gateway. Option C is wrong because outbound is allowed.
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 subnet's route table does not have a route to an internet gateway.
Why it's wrong here
It has a route.
The security group's outbound rules are too restrictive.
Why it's wrong here
Outbound traffic is allowed.
The network ACL's outbound rules are blocking traffic.
Why this is correct
Network ACLs are stateless and must allow both inbound and outbound.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
The instance does not have a public IP address.
Why it's wrong here
It has a public IP.
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 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.
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 DVA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Troubleshooting and Optimization — study guide chapter
Learn the concepts, then practise the questions
Troubleshooting and Optimization practice questions
Targeted practice on this topic area only
All DVA-C02 questions
1,616 questions across all exam domains
AWS Certified Developer Associate DVA-C02 study guide
Full concept coverage aligned to exam objectives
DVA-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 DVA-C02 questions linked to Development with AWS Services.
Practise DVA-C02 questions linked to Security.
Practise DVA-C02 questions linked to Deployment.
Practise DVA-C02 questions linked to Troubleshooting and Optimization.
Practise DVA-C02 questions linked to DVA-C02 fundamentals.
Practise DVA-C02 questions linked to DVA-C02 scenario.
Practise DVA-C02 questions linked to DVA-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
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — CIDR notation defines the prefix length..
The correct answer is: The network ACL's outbound rules are blocking traffic. — Option D is correct because a missing or misconfigured network ACL can block traffic even if security group allows it. Option A is wrong because the instance has a public IP. Option B is wrong because the route table has a route to an internet gateway. Option C is wrong because outbound is allowed.
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.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 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.
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.