- A
Network ACLs on the ALB subnet with deny rules
Why wrong: Network ACLs are stateless and affect all traffic, not targeted.
- B
AWS WAF with an IP set rule that blocks the malicious IPs
WAF integrates with ALB and can block IPs.
- C
AWS Shield Advanced with automatic IP blocking
Why wrong: Shield Advanced is for DDoS mitigation, not custom IP blocking.
- D
Security Groups for the ALB with deny rules
Why wrong: Security groups support allow rules only, not deny.
Question 1,196 of 1,705
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 has deployed a web application behind an Application Load Balancer (ALB) in a VPC. The security team wants to block a list of known malicious IP addresses from accessing the application. Which service should they use to implement this protection?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
AWS WAF with an IP set rule that blocks the malicious IPs
AWS WAF is a web application firewall that can inspect HTTP/S traffic and block requests based on conditions such as IP addresses. By creating an IP set containing the malicious IPs and associating it with a web ACL on the ALB, the security team can block those IPs at the application layer. This is more granular and efficient than network-level controls. Option A (Network ACLs) are stateless and operate at the subnet level, not designed for application-layer filtering, and would require managing deny rules that conflict with the default allow. Option C (AWS Shield Advanced) provides DDoS protection and cost protection, but does not offer granular IP blocking based on a custom list. Option D (Security Groups) are stateful firewalls that only support allow rules; they cannot deny specific IP addresses.
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.
- ✗
Network ACLs on the ALB subnet with deny rules
Why it's wrong here
Network ACLs are stateless and affect all traffic, not targeted.
- ✓
AWS WAF with an IP set rule that blocks the malicious IPs
- ✗
AWS Shield Advanced with automatic IP blocking
Why it's wrong here
Shield Advanced is for DDoS mitigation, not custom IP blocking.
- ✗
Security Groups for the ALB with deny rules
Why it's wrong here
Security groups support allow rules only, not deny.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
Visual reference
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
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.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
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: AWS WAF with an IP set rule that blocks the malicious IPs — AWS WAF is a web application firewall that can inspect HTTP/S traffic and block requests based on conditions such as IP addresses. By creating an IP set containing the malicious IPs and associating it with a web ACL on the ALB, the security team can block those IPs at the application layer. This is more granular and efficient than network-level controls. Option A (Network ACLs) are stateless and operate at the subnet level, not designed for application-layer filtering, and would require managing deny rules that conflict with the default allow. Option C (AWS Shield Advanced) provides DDoS protection and cost protection, but does not offer granular IP blocking based on a custom list. Option D (Security Groups) are stateful firewalls that only support allow rules; they cannot deny specific IP addresses.
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.
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Last reviewed: Jun 20, 2026
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