The correct answer is Azure Application Gateway on the web subnet and network security groups on the database subnet. This solution achieves multi-tier network isolation in Azure by placing the Application Gateway as a regional, layer-7 load balancer in front of the web tier, while NSGs on the database subnet enforce a strict inbound rule that only permits traffic from the web tier subnet, effectively blocking direct internet access to the database. On the AZ-305 exam, this scenario tests your ability to choose the simplest, most manageable service for east-west isolation within a VNet, often contrasting regional versus global services. A common trap is selecting Azure Firewall, which adds unnecessary overhead for simple subnet filtering, or Azure Front Door, which is a global service that cannot provide VNet-level isolation. Remember the memory tip: "Gateway for the web, NSG for the DB" — keep the database locked down with subnet-level rules, not a full firewall.
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 are designing a networking solution for a multi-tier application in Azure. The front-end web tier must be accessible from the internet, while the back-end database tier must only be accessible from the web tier. You need to minimize management overhead and ensure that the back-end tier is not directly reachable from the internet. What should you use?
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
✓
Azure Application Gateway on the web subnet and network security groups on the database subnet
Option C is correct. Azure Application Gateway can be placed in front of the web tier in a VNet, and network security groups (NSGs) on the database subnet can restrict inbound traffic to only the web tier subnet. Option A is wrong because Azure Front Door is a global load balancer, not a regional one, and does not provide VNet-level isolation. Option B is wrong because Azure Firewall is a managed firewall but adds unnecessary complexity; NSGs are simpler for subnet-level filtering. Option D is wrong because Azure Bastion is for RDP/SSH access, not for application traffic.
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 Application Gateway on the web subnet and network security groups on the database subnet
Why this is correct
Application Gateway provides internet-facing access to the web tier; NSGs restrict database traffic to the web subnet only.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Azure Bastion for database access and Azure Front Door for web access
Why it's wrong here
Bastion is for management, not for application traffic.
✗
Azure Front Door with private link for the web tier and service endpoints for the database tier
Why it's wrong here
Front Door is for global load balancing; service endpoints do not provide subnet-level isolation.
✗
Azure Firewall in a hub VNet with forced tunneling for all traffic
Why it's wrong here
Overly complex for this requirement; NSGs are sufficient.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-305 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-305 subnetting questions on CIDR, address ranges, and subnet selection.
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: Azure Application Gateway on the web subnet and network security groups on the database subnet — Option C is correct. Azure Application Gateway can be placed in front of the web tier in a VNet, and network security groups (NSGs) on the database subnet can restrict inbound traffic to only the web tier subnet. Option A is wrong because Azure Front Door is a global load balancer, not a regional one, and does not provide VNet-level isolation. Option B is wrong because Azure Firewall is a managed firewall but adds unnecessary complexity; NSGs are simpler for subnet-level filtering. Option D is wrong because Azure Bastion is for RDP/SSH access, not for application traffic.
What should I do if I get this AZ-305 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-305 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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