Question 75 of 999

Design infrastructure solutions →easyMultiple ChoiceObjective-mapped

Quick Answer

The answer is to deploy all tiers in the same VNet with separate subnets and use Network Security Groups (NSGs) to restrict traffic, placing an Azure Application Gateway with WAF in front of the web tier. This design achieves secure multi-tier network isolation by leveraging subnet-level segmentation within a single VNet, where NSGs act as stateful firewalls to explicitly allow only necessary traffic between tiers—such as web-to-API and API-to-database—while blocking all other flows, including direct internet access to the database. On the AZ-305 exam, this scenario tests your understanding of the principle of least privilege in network design, where the trap is overcomplicating with VNet peering or Azure Firewall when simple subnet isolation suffices. A common memory tip: think of the three-tier architecture as a castle with three locked rooms, where NSGs are the keys for each door, and the Application Gateway is the guarded front gate—never expose the treasure room (database) directly.

AZ-305 Design infrastructure solutions Practice Question

This AZ-305 practice question tests your understanding of design infrastructure solutions. 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 need to design a networking solution for a multi-tier application that includes a web front-end, an API layer, and a database. The web and API tiers must be accessible from the internet, while the database tier must be isolated. What is the most secure and efficient design?

Question 1easymultiple choice

Full question →

A
Place all VMs in the same subnet and use a single Azure Load Balancer to distribute traffic.
Why wrong: This exposes the database tier to internet traffic and reduces security.
B
Use separate VNets for each tier and connect them with VNet peering.
Why wrong: Unnecessarily complex; separate subnets within a VNet provide isolation.
C
Deploy all VMs in a single subnet and use Azure Firewall to inspect all inbound and outbound traffic.
Why wrong: Azure Firewall adds cost and complexity without proper tier isolation.
D
Deploy all tiers in the same VNet with separate subnets, and use NSGs to restrict traffic. Place an Azure Application Gateway with WAF in front of the web tier.
Secure and efficient: subnets isolate tiers, NSGs control traffic, Application Gateway provides internet-facing entry and WAF protection.

Full breakdown with real-world context →

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

✓

Deploy all tiers in the same VNet with separate subnets, and use NSGs to restrict traffic. Place an Azure Application Gateway with WAF in front of the web tier.

Option C is correct because using subnets for each tier with NSG restrictions provides isolation. Application Gateway with WAF protects the web tier. Option A (load balancer for all tiers) exposes the database. Option B (VNet peering) is not needed. Option D (Azure Firewall for all traffic) is overkill and complex.

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.

✗
Place all VMs in the same subnet and use a single Azure Load Balancer to distribute traffic.
Why it's wrong here
This exposes the database tier to internet traffic and reduces security.
✗
Use separate VNets for each tier and connect them with VNet peering.
Why it's wrong here
Unnecessarily complex; separate subnets within a VNet provide isolation.
✗
Deploy all VMs in a single subnet and use Azure Firewall to inspect all inbound and outbound traffic.
Why it's wrong here
Azure Firewall adds cost and complexity without proper tier isolation.
✓
Deploy all tiers in the same VNet with separate subnets, and use NSGs to restrict traffic. Place an Azure Application Gateway with WAF in front of the web tier.
Why this is correct
Secure and efficient: subnets isolate tiers, NSGs control traffic, Application Gateway provides internet-facing entry and WAF protection.
Related concept
CIDR notation defines the prefix length.

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 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

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 AZ-305 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this AZ-305 question test?

Design infrastructure solutions — This question tests Design infrastructure solutions — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Deploy all tiers in the same VNet with separate subnets, and use NSGs to restrict traffic. Place an Azure Application Gateway with WAF in front of the web tier. — Option C is correct because using subnets for each tier with NSG restrictions provides isolation. Application Gateway with WAF protects the web tier. Option A (load balancer for all tiers) exposes the database. Option B (VNet peering) is not needed. Option D (Azure Firewall for all traffic) is overkill and complex.

What should I do if I get this AZ-305 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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