The answer is AWS WAF, used to block an IP address from an SAP Application Load Balancer by creating an IP set and a blocking rule associated with the ALB. This works because AWS WAF operates at Layer 7, inspecting incoming HTTP/HTTPS requests before they reach the ALB, allowing you to filter traffic based on source IP addresses at the network edge. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding of where to apply IP-based filtering for SAP workloads behind an ALB, often as a trap against Security Groups, which only see the ALB’s private IP, or NACLs, which operate at the subnet level and cannot filter traffic to a managed ALB directly. A common memory tip is to remember that WAF is the only service that can inspect and block IPs at the application layer before the ALB processes the request, while Security Groups and NACLs are blind to the original client IP in this architecture.
PAS-C01 Operations and Maintenance Practice Question
This PAS-C01 practice question tests your understanding of operations and maintenance. 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.
An SAP administrator notices that the application logs show repeated authentication failures from a specific IP address. The SAP application is hosted on an EC2 instance behind an Application Load Balancer. What AWS service can be used to block traffic from that IP at the network level?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use AWS WAF to create an IP set and block rule, associated with the ALB.
Option C is correct because AWS WAF can be associated with an ALB to filter IP addresses. Option A is wrong because Security Groups are stateful and cannot block based on IP address in the context of an ALB (they see only the ALB's IP). Option B is wrong because NACLs are stateless and applied at the subnet level, but the ALB is a managed service; WAF is more appropriate. Option D is wrong because CloudFront is a CDN and not typically used solely for IP blocking in this scenario.
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.
✗
Use Amazon CloudFront with a geo-restriction to block the IP.
Why it's wrong here
CloudFront geo-restriction blocks by country, not specific IP, and adds unnecessary complexity.
✓
Use AWS WAF to create an IP set and block rule, associated with the ALB.
Why this is correct
AWS WAF can inspect source IP and block requests at the ALB level.
Update the security group of the EC2 instance to deny traffic from that IP.
Why it's wrong here
Security groups are stateful and apply to the instance, but traffic from ALB appears to come from the ALB's IP, not the original client IP.
✗
Add a network ACL rule to the subnet to deny traffic from that IP.
Why it's wrong here
NACLs are stateless and apply at the subnet level, but ALB traffic still originates from the ALB; also WAF is a more direct solution.
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 PAS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Operations and Maintenance — This question tests Operations and Maintenance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Use AWS WAF to create an IP set and block rule, associated with the ALB. — Option C is correct because AWS WAF can be associated with an ALB to filter IP addresses. Option A is wrong because Security Groups are stateful and cannot block based on IP address in the context of an ALB (they see only the ALB's IP). Option B is wrong because NACLs are stateless and applied at the subnet level, but the ALB is a managed service; WAF is more appropriate. Option D is wrong because CloudFront is a CDN and not typically used solely for IP blocking in this scenario.
What should I do if I get this PAS-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 PAS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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