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.
A company uses Azure Front Door to publish a web application globally. They need to protect against DDoS attacks and web application attacks (SQL injection, XSS). Which two services should they enable in combination?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Azure DDoS Protection Standard and Azure WAF policy on Front Door
Azure DDoS Protection protects against volumetric DDoS attacks. Azure Web Application Firewall (WAF) in Front Door protects against application-layer attacks. Azure Firewall is for network-layer filtering. Network Security Groups (NSGs) are for subnet-level filtering. Azure DDoS Protection Standard is the correct tier.
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.
✗
Azure DDoS Protection Standard and Azure Firewall
Why it's wrong here
Incorrect: Azure Firewall does not provide application-layer protection like WAF.
✗
Azure WAF on Application Gateway and Network Security Groups
Why it's wrong here
Incorrect: WAF on Application Gateway is for regional deployments, not global Front Door; NSGs don't protect at application layer.
✗
Azure Firewall and Azure DDoS Protection Basic
Why it's wrong here
Incorrect: Azure Firewall does not replace WAF for application attacks; DDoS Protection Basic is insufficient.
✓
Azure DDoS Protection Standard and Azure WAF policy on Front Door
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: Azure DDoS Protection Standard and Azure WAF policy on Front Door — Azure DDoS Protection protects against volumetric DDoS attacks. Azure Web Application Firewall (WAF) in Front Door protects against application-layer attacks. Azure Firewall is for network-layer filtering. Network Security Groups (NSGs) are for subnet-level filtering. Azure DDoS Protection Standard is the correct tier.
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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