Quick Answer
The answer is to configure NSGs on each subnet with appropriate allow rules. This is the minimum configuration for multi-tier subnet isolation using NSGs because each Network Security Group acts as a stateful firewall at the subnet level, allowing you to explicitly permit only the required traffic flows: internet to web, web to app, and app to db, while implicitly denying everything else. On the Microsoft Azure Security Engineer Associate AZ-500 exam, this scenario tests your understanding of least-privilege network segmentation and the distinction between native Azure tools and premium services—a common trap is over-engineering the solution with Azure Firewall or VNet peering when NSGs alone suffice. Remember that NSGs are free, built-in, and applied directly to subnets within the same VNet, making them the simplest and most cost-effective choice for this isolation pattern. A helpful memory tip: think of the three-tier handshake—web opens to the world, app talks only to web, db talks only to app—and let NSGs enforce each handshake with a single allow rule per subnet.
This AZ-500 practice question tests your understanding of secure networking. 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.
You are designing a network security solution for a multi-tier application in Azure. The web tier must be accessible from the internet, the application tier only from the web tier, and the database tier only from the application tier. All tiers are in different subnets of the same VNet. What is the minimum configuration?
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.
Use service endpoints for each tier.
Why wrong: Service endpoints are for Azure services, not subnet isolation.
Create separate VNets for each tier and use VNet peering.
Why wrong: More complex than necessary.
Deploy Azure Firewall in the VNet and route all traffic through it.
Why wrong: Overkill and adds cost.
Configure NSGs on each subnet with appropriate allow rules.
NSGs can filter traffic between subnets.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Configure NSGs on each subnet with appropriate allow rules.
Option A is correct because NSGs on each subnet can control inbound traffic: allow internet to web, allow web to app, allow app to db. Option B is wrong because Azure Firewall is not required. Option C is wrong because VNet peering is not needed. Option D is wrong because service endpoints are for Azure services.
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.
Use service endpoints for each tier.
Why it's wrong here
Service endpoints are for Azure services, not subnet isolation.
Create separate VNets for each tier and use VNet peering.
Why it's wrong here
More complex than necessary.
Deploy Azure Firewall in the VNet and route all traffic through it.
Why it's wrong here
Overkill and adds cost.
Configure NSGs on each subnet with appropriate allow rules.
Why this is correct
NSGs can filter traffic between subnets.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
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 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.
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 AZ-500 subnetting questions on CIDR, address ranges, and subnet selection.
Secure networking — study guide chapter
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FAQ
Secure networking — This question tests Secure networking — CIDR notation defines the prefix length..
The correct answer is: Configure NSGs on each subnet with appropriate allow rules. — Option A is correct because NSGs on each subnet can control inbound traffic: allow internet to web, allow web to app, allow app to db. Option B is wrong because Azure Firewall is not required. Option C is wrong because VNet peering is not needed. Option D is wrong because service endpoints are for Azure services.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related AZ-500 subnetting questions on CIDR, address ranges, and subnet selection.
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.
CIDR notation defines the prefix length.
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are designing network security for a three-tier application. You need to isolate each tier (web, application, data) and control traffic between them. Which TWO Azure services should you use to achieve this? (Choose two.)
mediumWhy A: Options A and C are correct. NSGs provide traffic filtering at the subnet or NIC level. ASGs allow grouping of VMs and referencing them in NSG rules. Option B is wrong because Azure Firewall is a centralized firewall, but for simple tier isolation, NSGs and ASGs suffice. Option D is wrong because VNet peering connects VNets, not tiers within a VNet. Option E is wrong because Azure Policy does not enforce network traffic rules.
Variation 2. You are designing network security for a multi-tier application. The web tier must be accessible from the internet, but the database tier must only be accessible from the web tier. Both tiers are in the same virtual network. Which Azure service should you use to restrict traffic between the tiers?
easyWhy B: Option C is correct because a Network Security Group (NSG) can be associated with the subnet or NIC of the database tier to allow only inbound traffic from the web tier's private IP addresses or subnet. Option A is wrong because Application Security Groups (ASGs) are used to group VMs but still require NSG rules. Option B is wrong because Azure Firewall is a managed firewall, but it's overkill and costlier than an NSG for simple subnet-to-subnet filtering. Option D is wrong because a route table controls routing, not filtering.
Variation 3. You are designing a network security solution for a multi-tier application running in Azure. The front-end VMs must only accept traffic from Azure Front Door. Back-end VMs must only accept traffic from the front-end tier. You plan to use NSGs and ASGs. Which configuration should you use to meet these requirements with minimal administrative overhead?
mediumWhy D: Option C is correct because using Application Security Groups (ASGs) allows you to define network security policies based on application groups, and you can reference an ASG as the source or destination in NSG rules. By placing front-end VMs in an ASG and back-end VMs in another ASG, you can create NSG rules that restrict traffic accordingly. Option A is wrong because using individual VM IP addresses is not scalable. Option B is wrong because service tags for Azure Front Door exist, but they don't cover front-end VMs. Option D is wrong because VNet peering alone does not provide traffic filtering.
Last reviewed: Jun 20, 2026
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