This AZ-500 practice question tests your understanding of secure networking. 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 secure network architecture for a three-tier application. The web tier must be accessible from the internet, while the application and database tiers must only be accessible from the web tier. Which Azure service should you use to isolate the tiers most securely?
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) on subnets
Option A is correct because NSGs with subnet-level rules can restrict traffic between tiers. Option B is wrong because Azure Firewall is a centralized firewall, but for simple tier isolation, NSGs are more appropriate and cost-effective. Option C is wrong because VNet peering connects networks, not isolates tiers. Option D is wrong because Azure Front Door is for global load balancing, not tier isolation.
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 Firewall with application rules
Why it's wrong here
Overkill for simple tier isolation; NSGs are sufficient.
✗
Azure Front Door with Web Application Firewall
Why it's wrong here
Front Door is for internet-facing web apps, not for internal tier isolation.
✓
Network security groups (NSGs) on subnets
Why this is correct
NSGs allow fine-grained inbound/outbound rules between subnets.
Peering connects VNets, but you still need NSGs for isolation.
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 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-500 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 AZ-500 subnetting questions on CIDR, address ranges, and subnet selection.
Secure networking — This question tests Secure networking — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Network security groups (NSGs) on subnets — Option A is correct because NSGs with subnet-level rules can restrict traffic between tiers. Option B is wrong because Azure Firewall is a centralized firewall, but for simple tier isolation, NSGs are more appropriate and cost-effective. Option C is wrong because VNet peering connects networks, not isolates tiers. Option D is wrong because Azure Front Door is for global load balancing, not tier isolation.
What should I do if I get this AZ-500 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 AZ-500 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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