- A
Deploy Azure Firewall with threat intelligence-based filtering enabled. Use Sentinel to generate alerts when SMB traffic is detected, and manually block IPs.
Why wrong: Manual intervention required; does not automate blocking.
- B
Use Microsoft Defender for Cloud to detect ransomware and deploy a third-party firewall in VPC. Configure Sentinel to send alerts to the firewall API.
Why wrong: VPC is an AWS concept; not applicable to Azure.
- C
Integrate Microsoft Defender for Identity with Sentinel. Create a playbook that automatically adds malicious IPs to a custom Azure Firewall policy, and use Sentinel incidents for investigation.
Defender for Identity detects lateral movement via SMB; playbook automates blocking via Azure Firewall; incidents provide forensic data.
- D
Enable network security groups (NSGs) on all subnets. Use Sentinel to detect SMB anomalies and apply NSG rules via Azure Policy.
Why wrong: NSGs cannot block based on real-time threat intelligence; Azure Policy is for compliance, not incident response.
Quick Answer
The correct answer is to integrate Microsoft Defender for Identity with Sentinel, creating a playbook that automatically adds malicious IPs to a custom Azure Firewall policy while using Sentinel incidents for investigation. This design works because Defender for Identity detects SMB-based ransomware behavior, such as anomalous lateral movement or brute-force attempts, and feeds those alerts into Sentinel, where a playbook triggers an automated block on Azure Firewall—providing both network-level prevention and forensic evidence without manual intervention. On the Microsoft Cybersecurity Architect exam, this scenario tests your ability to combine detection (Defender for Identity), automation (Sentinel playbooks), and enforcement (Azure Firewall) into a cohesive hybrid security solution; a common trap is choosing NSG rules, which lack real-time threat intel integration, or confusing Azure Firewall with AWS VPC. Remember the mnemonic “D.A.B.”—Detect with Defender, Automate with playbooks, Block with Azure Firewall.
SC-100 Design security solutions for infrastructure Practice Question
This SC-100 practice question tests your understanding of design security solutions for infrastructure. 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.
You are a security architect at a global manufacturing company. The company uses a hybrid infrastructure with on-premises Active Directory and Azure. They have recently deployed Microsoft Sentinel as their SIEM. The security team wants to detect and investigate ransomware attacks that spread via SMB. The CISO has requested a solution that can automatically block malicious IPs at the network level and provide forensic evidence. You need to design a solution that meets these requirements with minimal manual intervention. What should you include in your design?
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
Integrate Microsoft Defender for Identity with Sentinel. Create a playbook that automatically adds malicious IPs to a custom Azure Firewall policy, and use Sentinel incidents for investigation.
Option C uses Microsoft Defender for Identity to detect SMB-based attacks and Azure Firewall to block IPs via playbooks. Option A uses Azure Firewall alone without detection; Option B uses NSG but cannot block based on real-time threat intel; Option D uses VPC (AWS) which is not applicable.
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.
- ✗
Deploy Azure Firewall with threat intelligence-based filtering enabled. Use Sentinel to generate alerts when SMB traffic is detected, and manually block IPs.
Why it's wrong here
Manual intervention required; does not automate blocking.
- ✗
Use Microsoft Defender for Cloud to detect ransomware and deploy a third-party firewall in VPC. Configure Sentinel to send alerts to the firewall API.
Why it's wrong here
VPC is an AWS concept; not applicable to Azure.
- ✓
Integrate Microsoft Defender for Identity with Sentinel. Create a playbook that automatically adds malicious IPs to a custom Azure Firewall policy, and use Sentinel incidents for investigation.
- ✗
Enable network security groups (NSGs) on all subnets. Use Sentinel to detect SMB anomalies and apply NSG rules via Azure Policy.
Why it's wrong here
NSGs cannot block based on real-time threat intelligence; Azure Policy is for compliance, not incident response.
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 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 SC-100 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this SC-100 question test?
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: Integrate Microsoft Defender for Identity with Sentinel. Create a playbook that automatically adds malicious IPs to a custom Azure Firewall policy, and use Sentinel incidents for investigation. — Option C uses Microsoft Defender for Identity to detect SMB-based attacks and Azure Firewall to block IPs via playbooks. Option A uses Azure Firewall alone without detection; Option B uses NSG but cannot block based on real-time threat intel; Option D uses VPC (AWS) which is not applicable.
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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Last reviewed: Jun 21, 2026
This SC-100 practice question is part of Courseiva's free Microsoft 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 SC-100 exam.
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