The answer is to add an AWS WAF rule using the 'IP reputation lists' managed rule group to block malicious IPs. This is the most efficient approach because AWS WAF’s managed rule group is pre-configured and continuously updated by AWS threat intelligence to automatically block known malicious IP addresses without requiring manual maintenance of a growing block list. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of when to use managed rule groups versus manual security group or NACL updates—a common trap is trying to solve application-layer blocking with network-layer controls like security groups or stateless NACLs, which are not designed for dynamic IP reputation lists. Remember the memory tip: for malicious IPs at the application layer, think “managed reputation, not manual configuration.”
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 company hosts a web application on EC2 instances in an Auto Scaling group behind an Application Load Balancer (ALB). The security team wants to block a list of known malicious IP addresses from accessing the application. They have already created an AWS WAF web ACL and associated it with the ALB. What is the MOST efficient way to block the IP addresses?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add an AWS WAF rule to the web ACL that uses the 'IP reputation lists' managed rule group to block malicious IPs.
Option B is correct because AWS WAF has a managed rule group 'IP reputation lists' that automatically blocks known malicious IPs. Option A is wrong because updating security groups is not scalable for a large list. Option C is wrong because Network ACLs are stateless and not designed for application-layer blocking. Option D is wrong because CloudFront is an additional layer not mentioned and would add complexity.
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.
✗
Place a CloudFront distribution in front of the ALB and use CloudFront's geo-restriction feature.
Why it's wrong here
Wrong: Geo-restriction blocks by country, not specific IPs.
✓
Add an AWS WAF rule to the web ACL that uses the 'IP reputation lists' managed rule group to block malicious IPs.
Why this is correct
Correct: Managed rule group automatically blocks known malicious IPs.
Configure a network ACL on the ALB's subnet to deny inbound traffic from each malicious IP.
Why it's wrong here
Wrong: NACLs are stateless and not suitable for application-layer blocking.
✗
Add each IP address as an inbound deny rule in the security group of the ALB.
Why it's wrong here
Wrong: Security groups have limits and are not designed for large IP blocklists.
Common exam traps
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 ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Add an AWS WAF rule to the web ACL that uses the 'IP reputation lists' managed rule group to block malicious IPs. — Option B is correct because AWS WAF has a managed rule group 'IP reputation lists' that automatically blocks known malicious IPs. Option A is wrong because updating security groups is not scalable for a large list. Option C is wrong because Network ACLs are stateless and not designed for application-layer blocking. Option D is wrong because CloudFront is an additional layer not mentioned and would add complexity.
What should I do if I get this ANS-C01 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 ANS-C01 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 →
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.