The correct design is to deploy Azure Firewall in each region with forced tunneling enabled, using an active-active configuration. This ensures all traffic between on-premises and Azure—both inbound and outbound—is inspected by the firewall without introducing a single point of failure, while minimizing latency by keeping inspection local to each region. Forced tunneling directs all internet-bound traffic from Azure back through the firewall and ExpressRoute, guaranteeing full inspection. On the Microsoft Cybersecurity Architect exam, this scenario tests your understanding of how to combine multi-region resilience with forced tunneling for compliance and security, often appearing as a trap where candidates mistakenly choose a single hub firewall or rely on NSGs, which only filter and cannot inspect traffic. A key memory tip is “local inspection, global compliance”—each region’s firewall inspects its own traffic, while forced tunneling ensures no traffic bypasses the security boundary.
SC-100 Design security solutions for infrastructure Practice Question
This SC-100 practice question tests your understanding of design security solutions for infrastructure. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 has a multi-region Azure deployment with ExpressRoute connections to on-premises. You need to design a solution that ensures all traffic between on-premises and Azure is inspected by a firewall for both inbound and outbound connections. The solution must minimize latency and avoid a single point of failure. What design should you recommend?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Deploy Azure Firewall in each region with forced tunneling enabled
Option D is correct because deploying Azure Firewall in each region in an active-active configuration with forced tunneling provides inspection for all traffic without a single point of failure. Option A is wrong because a single firewall is a single point of failure and adds latency for all traffic. Option B is wrong because NSGs do not inspect traffic, they filter based on rules. Option C is wrong because a third-party NVA in a single hub introduces a single point of failure and potential licensing complexity.
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 in each region with forced tunneling enabled
Why this is correct
Regional firewalls avoid single point of failure and minimize latency with forced tunneling for inspection.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Deploy Azure Firewall in one central hub region and route all traffic through it
Why it's wrong here
Single point of failure and increased latency for remote regions.
✗
Use Network Security Groups (NSGs) on subnets to filter traffic
Why it's wrong here
NSGs do not inspect traffic, they only filter by rule.
✗
Deploy a third-party NVA in a hub-and-spoke topology with a single hub
Why it's wrong here
Single point of failure and potential licensing complexity.
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.
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: Deploy Azure Firewall in each region with forced tunneling enabled — Option D is correct because deploying Azure Firewall in each region in an active-active configuration with forced tunneling provides inspection for all traffic without a single point of failure. Option A is wrong because a single firewall is a single point of failure and adds latency for all traffic. Option B is wrong because NSGs do not inspect traffic, they filter based on rules. Option C is wrong because a third-party NVA in a single hub introduces a single point of failure and potential licensing complexity.
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.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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