The answer is to use network ACLs as a stateless layer of defense for subnets, alongside security groups as a stateful virtual firewall and AWS Shield Advanced for DDoS protection. This combination works because security groups operate at the instance level with allow rules only, while network ACLs provide a stateless, subnet-level filter that can explicitly deny traffic, creating a defense-in-depth architecture. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept tests your understanding of layered security controls within a VPC, often appearing in scenario-based questions where you must choose the correct mix of stateful and stateless protections. A common trap is assuming that allowing all outbound traffic is acceptable, but best practices require restricting egress to only necessary destinations. Remember the mnemonic: "SANS" for Security groups (stateful), ACLs (stateless), Network segmentation, and Shield (DDoS).
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.
Which THREE of the following are best practices for securing a VPC? (Choose three.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable AWS Shield Advanced for DDoS protection.
Options A, B, and D are correct. Using security groups as a virtual firewall is a best practice. Using network ACLs as a second layer of defense is also recommended. AWS Shield Advanced is a managed DDoS protection service that should be enabled for VPCs with public endpoints. Option C is incorrect because allowing all outbound traffic is not a security best practice; it should be restricted. Option E is incorrect because default security group should not allow all traffic; it should be restrictive.
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.
✓
Enable AWS Shield Advanced for DDoS protection.
Why this is correct
AWS Shield Advanced provides enhanced DDoS protection for VPC resources.
Clue confirmation
The clue word "best" in the question point toward this answer.
Allow all outbound traffic from the VPC to the internet.
Why it's wrong here
Outbound traffic should be restricted based on least privilege.
✗
Assign a default security group that allows all traffic.
Why it's wrong here
The default security group should be restrictive, not allow all traffic.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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: Enable AWS Shield Advanced for DDoS protection. — Options A, B, and D are correct. Using security groups as a virtual firewall is a best practice. Using network ACLs as a second layer of defense is also recommended. AWS Shield Advanced is a managed DDoS protection service that should be enabled for VPCs with public endpoints. Option C is incorrect because allowing all outbound traffic is not a security best practice; it should be restricted. Option E is incorrect because default security group should not allow all traffic; it should be restrictive.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO of the following are best practices for securing a VPC?
easy
A.Enable VPC Flow Logs on all subnets to block malicious traffic.
✓ B.Use multiple Availability Zones for redundancy.
C.Place database instances in public subnets for easier management.
✓ D.Restrict inbound SSH access to specific IP ranges.
E.Use the default VPC security group for all instances.
Why B: Option A is correct: Using multiple Availability Zones improves resilience and security. Option B is correct: Limiting inbound SSH access to specific IP addresses reduces attack surface. Option C is wrong: Public subnets should not have direct internet access for databases. Option D is wrong: Default VPC security group allows all inbound traffic. Option E is wrong: Flow logs do not block traffic.
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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
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