The correct answer is to implement Azure Firewall, network security groups (NSGs), and Azure DDoS Protection as the three network security measures for a defense-in-depth strategy in an Azure multi-tier application. Azure Firewall acts as a centralized, stateful firewall to filter inbound and outbound traffic across the entire virtual network, while NSGs provide micro-segmentation by controlling traffic between subnets or individual NICs, enforcing least-privilege access between application tiers. Azure DDoS Protection mitigates volumetric attacks at the network layer, ensuring availability. On the Microsoft Cybersecurity Architect exam, this scenario tests your ability to layer controls from the perimeter down to the subnet level, avoiding common traps like confusing VPN gateways (which handle connectivity, not security) or Azure Front Door (which is specific to web application delivery, not general network defense). A useful memory tip is to think of the three layers as "Firewall for the edge, NSGs for the middle, DDoS for the flood."
SC-100 Design security solutions for infrastructure Practice Question
This SC-100 practice question tests your understanding of design security solutions for infrastructure. 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.
Your organization is implementing a defense-in-depth strategy for a multi-tier application hosted on Azure. You need to secure the network layers. Which THREE measures should you implement?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable Azure DDoS Protection on the virtual network.
Option B is correct because Azure Firewall provides centralized inbound and outbound traffic filtering. Option C is correct because network security groups (NSGs) provide micro-segmentation at the subnet or NIC level. Option D is correct because Azure DDoS Protection helps mitigate volumetric attacks. Option A is wrong because a VPNgateway is for connectivity, not a network security layer. Option E is wrong because Azure Front Door is an application delivery and security service, but it is not a general network security layer for all tiers; it is more specific to web applications.
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 Azure DDoS Protection on the virtual network.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this SC-100 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SC-100 subnetting questions on CIDR, address ranges, and subnet selection.
Design security solutions for infrastructure — This question tests Design security solutions for infrastructure — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Enable Azure DDoS Protection on the virtual network. — Option B is correct because Azure Firewall provides centralized inbound and outbound traffic filtering. Option C is correct because network security groups (NSGs) provide micro-segmentation at the subnet or NIC level. Option D is correct because Azure DDoS Protection helps mitigate volumetric attacks. Option A is wrong because a VPN gateway is for connectivity, not a network security layer. Option E is wrong because Azure Front Door is an application delivery and security service, but it is not a general network security layer for all tiers; it is more specific to web applications.
What should I do if I get this SC-100 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 SC-100 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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