The answer is to create an AWS WAF web ACL with IP set rules and associate it with the Application Load Balancer. This is the most efficient approach because AWS WAF is purpose-built to filter HTTP/HTTPS traffic at the application layer, allowing you to block specific IP addresses directly at the ALB without managing stateless rules or complex configurations. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of when to use WAF versus network-layer controls like NACLs or security groups—a common trap is confusing stateless NACLs (which require return traffic rules) with the stateful, application-aware filtering of WAF. Remember that security groups cannot deny specific IPs, and route tables do not filter traffic at all. Memory tip: think "WAF for the web, NACL for the network"—if you need to block IPs hitting an ALB, WAF is your direct, exam-approved tool.
SOA-C02 Networking and Content Delivery Practice Question
This SOA-C02 practice question tests your understanding of networking and content delivery. 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 sysadmin needs to block specific IP addresses from accessing an Application Load Balancer. Which approach is MOST efficient?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create an AWS WAF web ACL with IP set rules and associate it with the ALB.
Option B is correct because AWS WAF can be associated with an ALB to filter traffic based on IP addresses. Option A is wrong because NACLs are stateless and not as efficient for ALB. Option C is wrong because security groups cannot block specific IPs. Option D is wrong because route tables don't filter traffic.
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.
✗
Modify the security group for the ALB to deny traffic from those IPs.
Why it's wrong here
Security groups do not support deny rules.
✗
Add a route in the VPC route table to drop traffic from those IPs.
Why it's wrong here
Route tables cannot drop traffic based on source IP.
✓
Create an AWS WAF web ACL with IP set rules and associate it with the ALB.
Why this is correct
WAF provides IP blocking at the ALB level efficiently.
NACLs are stateless and require separate inbound/outbound rules.
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 SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Networking and Content Delivery — This question tests Networking and Content Delivery — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create an AWS WAF web ACL with IP set rules and associate it with the ALB. — Option B is correct because AWS WAF can be associated with an ALB to filter traffic based on IP addresses. Option A is wrong because NACLs are stateless and not as efficient for ALB. Option C is wrong because security groups cannot block specific IPs. Option D is wrong because route tables don't filter traffic.
What should I do if I get this SOA-C02 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 SOA-C02 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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