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.
You are designing a network security solution for a multi-tier application hosted in Azure. The front-end web tier must be accessible from the internet, but the back-end database tier must only accept traffic from the front-end tier. Which Azure service should you use to enforce this restriction?
Azure Firewall
Why wrong: Azure Firewall provides centralized network security, but NSGs are simpler for subnet-level filtering.
Network Security Groups (NSGs)
NSGs filter traffic between subnets based on rules.
Azure Bastion
Why wrong: Azure Bastion provides secure remote access, not network segmentation.
Application Gateway
Why wrong: Application Gateway is a layer 7 load balancer, not a network filter.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Network Security Groups (NSGs)
Option A is correct because Network Security Groups (NSGs) can be used to filter traffic between subnets. By applying an NSG to the database subnet with a rule allowing inbound traffic only from the front-end subnet's IP range, you restrict access. Option B is wrong because Azure Firewall is a managed firewall service, but for simple subnet-level filtering, NSGs are more appropriate and cost-effective. Option C is wrong because Application Gateway is a layer 7 load balancer. Option D is wrong because Azure Bastion provides secure RDP/SSH access to VMs.
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
For each option: why learners choose it and why it is or isn't the right answer here.
Azure Firewall
Why it's wrong here
Azure Firewall provides centralized network security, but NSGs are simpler for subnet-level filtering.
Network Security Groups (NSGs)
Why this is correct
NSGs filter traffic between subnets based on rules.
Related concept
CIDR notation defines the prefix length.
Azure Bastion
Why it's wrong here
Azure Bastion provides secure remote access, not network segmentation.
Application Gateway
Why it's wrong here
Application Gateway is a layer 7 load balancer, not a network filter.
Common exam traps
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
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.
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
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
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
Design security solutions for infrastructure — This question tests Design security solutions for infrastructure — CIDR notation defines the prefix length..
The correct answer is: Network Security Groups (NSGs) — Option A is correct because Network Security Groups (NSGs) can be used to filter traffic between subnets. By applying an NSG to the database subnet with a rule allowing inbound traffic only from the front-end subnet's IP range, you restrict access. Option B is wrong because Azure Firewall is a managed firewall service, but for simple subnet-level filtering, NSGs are more appropriate and cost-effective. Option C is wrong because Application Gateway is a layer 7 load balancer. Option D is wrong because Azure Bastion provides secure RDP/SSH access to VMs.
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.
CIDR notation defines the prefix length.
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Last reviewed: Jun 21, 2026
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