This ANS-C01 practice question tests your understanding of network design. 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.
Refer to the exhibit. An EC2 instance launched in subnet-1a is unable to access the internet. Which 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Subnet-1a does not assign public IP addresses automatically.
Option C is correct because if subnet-1a does not have the 'Auto-assign public IPv4 address' setting enabled, EC2 instances launched in that subnet will not receive a public IP address automatically. Without a public IP, the instance cannot communicate with the internet through an internet gateway, even if the route table has a default route (0.0.0.0/0) pointing to the internet gateway. The instance would need an Elastic IP or a public IP assigned at launch to enable internet access.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 route table rtb-main does not have a default route to the internet gateway.
Why it's wrong here
It does have a route to igw-12345.
✗
The VPC does not have DNS hostnames enabled.
Why it's wrong here
EnableDnsHostnames is true.
✓
Subnet-1a does not assign public IP addresses automatically.
Why this is correct
MapPublicIpOnLaunch is false, so instances lack public IPs.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Subnet-1a is not associated with any route table.
Why it's wrong here
It is associated with rtb-main.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The ANS-C01 exam often tests the misconception that a missing default route is the only cause for internet access failure, but the trap here is that even with a correct route, the instance must have a public IP (via auto-assign or Elastic IP) for the internet gateway to forward traffic back to it.
Detailed technical explanation
How to think about this question
When an EC2 instance in a public subnet lacks a public IP, the internet gateway cannot perform source network address translation (SNAT) because the instance's private IP is not routable on the internet. The instance can still send traffic to the internet gateway, but the gateway drops the return traffic since it has no mapping to a public IP. In contrast, if the instance had an Elastic IP assigned, it would work even without auto-assign public IP, as the Elastic IP provides a persistent public address.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Subnet-1a does not assign public IP addresses automatically. — Option C is correct because if subnet-1a does not have the 'Auto-assign public IPv4 address' setting enabled, EC2 instances launched in that subnet will not receive a public IP address automatically. Without a public IP, the instance cannot communicate with the internet through an internet gateway, even if the route table has a default route (0.0.0.0/0) pointing to the internet gateway. The instance would need an Elastic IP or a public IP assigned at launch to enable internet access.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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Question Discussion
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