DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. 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 company runs a web application on EC2 instances behind an ALB. The security team notices that the ALB is receiving a large number of requests from a single IP address, causing high CPU on the instances. They want to block this IP at the load balancer level without affecting other traffic. The ALB currently has a default action of forwarding to the target group. What is the MOST effective way to block this IP?
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 an IP match condition and associate it with the ALB.
Option B is correct because AWS WAF can be integrated with ALB to create a rule that blocks requests from a specific IP address. Option A is wrong because security groups cannot deny traffic; they only allow. Option C is wrong because modifying the listener rule's target group would not block the IP; it would just route elsewhere. Option D is wrong because the network ACL is for subnets, not for the ALB directly, and would affect all traffic to the subnets.
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.
✗
Update the network ACL for the VPC subnets to deny inbound traffic from that IP.
Why it's wrong here
This would block all traffic to the subnets, not just the ALB, and would affect other resources.
✗
Add a deny rule in the ALB's security group for the source IP.
Why it's wrong here
Security groups only support allow rules, not deny.
✗
Change the listener rule to forward requests from that IP to a different target group with no instances.
Why it's wrong here
ALB listener rules do not evaluate source IP; they route based on path/host/etc.
✓
Create an AWS WAF web ACL with an IP match condition and associate it with the ALB.
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 DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Incident and Event Response — This question tests Incident and Event Response — 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 an IP match condition and associate it with the ALB. — Option B is correct because AWS WAF can be integrated with ALB to create a rule that blocks requests from a specific IP address. Option A is wrong because security groups cannot deny traffic; they only allow. Option C is wrong because modifying the listener rule's target group would not block the IP; it would just route elsewhere. Option D is wrong because the network ACL is for subnets, not for the ALB directly, and would affect all traffic to the subnets.
What should I do if I get this DOP-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 DOP-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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