The answer is to update the ALB security group to allow inbound HTTPS only from the CloudFront managed prefix list, specifically `com.amazonaws.global.cloudfront.origin-facing`. This is the correct choice because a managed prefix list dynamically tracks all of CloudFront’s current IP ranges, automatically updating as CloudFront adds or removes addresses, which eliminates the risk of stale IPs and blocks direct traffic from non-CloudFront sources. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of origin security best practices, often trapping candidates who rely solely on custom headers (which can be spoofed) or AWS WAF alone (which adds complexity without addressing the core network-layer restriction). The key insight is that a security group rule referencing a managed prefix list provides a native, serverless, and automatically maintained boundary at the VPC level. Memory tip: think “prefix list for prefix protection”—if you see “restrict ALB to CloudFront” on the exam, your first instinct should be the managed prefix list, not headers or WAF.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 global e-commerce company uses AWS CloudFront to distribute content. They have an origin behind an Application Load Balancer (ALB) in a VPC. The ALB is internet-facing and has a security group that allows inbound HTTPS traffic from CloudFront's IP ranges. Users in some regions report slow loading times. The company wants to reduce latency and improve performance. They are considering using Lambda@Edge and origin failover. However, they also notice that the ALB is receiving traffic directly from some IPs that are not CloudFront IPs, causing unnecessary load. What should a network engineer do to restrict access to the ALB to only CloudFront?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Update the ALB security group to allow inbound HTTPS only from the CloudFront managed prefix list
The best practice is to restrict ALB security group to CloudFront managed prefix list (com.amazonaws.global.cloudfront.origin-facing). This dynamically allows CloudFront IPs. Option A (custom header) is good but not sufficient alone because attackers can mimic headers. Option B (AWS WAF) can help but is not the primary method. Option D (restrict to specific regions) is not precise.
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.
✓
Update the ALB security group to allow inbound HTTPS only from the CloudFront managed prefix list
Read the scenario before looking for a memorised answer.
✗
Use AWS WAF to block requests that do not come from CloudFront IPs
Why it's wrong here
WAF can be used but security group is simpler and more effective.
✗
Configure the ALB to require a custom header (e.g., X-Origin-Verify) and validate it in the origin
Why it's wrong here
Custom header is a best practice but can be spoofed; security group is more fundamental.
✗
Set up a VPC endpoint for CloudFront to route traffic privately
Why it's wrong here
CloudFront does not use VPC endpoints; it's a global service.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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.
What to study next
Got this wrong? Here's your next step.
Identify which ANS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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: Update the ALB security group to allow inbound HTTPS only from the CloudFront managed prefix list — The best practice is to restrict ALB security group to CloudFront managed prefix list (com.amazonaws.global.cloudfront.origin-facing). This dynamically allows CloudFront IPs. Option A (custom header) is good but not sufficient alone because attackers can mimic headers. Option B (AWS WAF) can help but is not the primary method. Option D (restrict to specific regions) is not precise.
What should I do if I get this ANS-C01 question wrong?
Identify which ANS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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.