This ANS-C01 practice question tests your understanding of network implementation. 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 network engineer created the CloudFormation stack shown. After creation, an EC2 instance launched in PublicSubnet does not have a public IP address. What is the most likely reason?
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
✓
The VPC does not have an Internet Gateway attached
Option A is correct because an EC2 instance in a public subnet requires an Internet Gateway (IGW) attached to the VPC to receive a public IP address. Without an IGW, the instance cannot be assigned a public IP or communicate with the internet, even if the subnet is configured to auto-assign public IPs. The CloudFormation stack likely omitted the IGW resource or its attachment to the VPC, leaving the VPC isolated.
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 VPC does not have an Internet Gateway attached
Why this is correct
Without an Internet Gateway, instances cannot be assigned public IPs or reach the internet.
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.
✗
The subnet does not have an Internet Gateway attached
Why it's wrong here
Internet Gateway is attached to the VPC, not the subnet.
✗
The subnet's route table does not have a route to a NAT Gateway
Why it's wrong here
NATGateway is for private subnets; public subnets use Internet Gateway.
✗
The instance type does not support public IP addresses
Why it's wrong here
All EC2 instance types support public IP assignment.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The ANS-C01 exam often tests the misconception that a NATGateway is required for public IP assignment, but the correct requirement is an Internet Gateway attached to the VPC with a route in the subnet's route table.
Detailed technical explanation
How to think about this question
When an EC2 instance is launched in a subnet with 'Auto-assign public IPv4 address' enabled, the VPC's DHCP option set and the subnet's route table must include a default route (0.0.0.0/0) pointing to an Internet Gateway for the public IP to be assigned and for traffic to route correctly. Without the IGW attachment, the VPC's internet gateway ID is null, causing the subnet's auto-assign feature to fail silently—the instance gets only a private IP. In CloudFormation, this often occurs when the AWS::EC2::InternetGateway resource is defined but not attached via AWS::EC2::VPCGatewayAttachment, or the attachment is missing entirely.
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 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.
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 Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The VPC does not have an Internet Gateway attached — Option A is correct because an EC2 instance in a public subnet requires an Internet Gateway (IGW) attached to the VPC to receive a public IP address. Without an IGW, the instance cannot be assigned a public IP or communicate with the internet, even if the subnet is configured to auto-assign public IPs. The CloudFormation stack likely omitted the IGW resource or its attachment to the VPC, leaving the VPC isolated.
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.
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 →
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.
This ANS-C01 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 ANS-C01 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.