The answer is that the subnet does not have a service endpoint for Microsoft.Storage enabled. Even though the subnet ID matches the virtual network rule in the Azure Storage firewall, traffic from the VM is still blocked because the subnet must explicitly delegate a service endpoint to Microsoft.Storage for the rule to take effect. Without this endpoint, the VM’s traffic is routed over the public internet and is denied by the storage account’s default Deny action. On the Microsoft Azure Solutions Architect Expert AZ-305 exam, this scenario tests your understanding of how virtual network service endpoints bridge Azure PaaS services to specific subnets, a common trap where candidates assume a listed subnet alone is sufficient. Remember the memory tip: “Rule lists the subnet, but the endpoint is the key—no endpoint, no entry.”
AZ-305 Design infrastructure solutions Practice Question
This AZ-305 practice question tests your understanding of design infrastructure solutions. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Refer to the exhibit. You have an Azure Storage account with the settings shown. A developer reports that they cannot access the storage account from their Azure VM that is connected to subnet-a. The VM's subnet ID matches the one in the rule. What is the most likely cause of the issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The subnet does not have a service endpoint for Microsoft.Storage enabled
The network rule set has defaultAction set to Deny, and only virtual network rules are configured. For traffic from a VM in subnet-a to be allowed, the VM's subnet must be listed. However, the VM might not have a service endpoint enabled for Microsoft.Storage on that subnet. Option A is wrong because the subnet is listed. Option C is wrong because HTTPS is enabled. Option D is wrong because GRS does not prevent access.
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.
✗
The storage account requires HTTPS and the VM is using HTTP
Why it's wrong here
supportsHttpsTrafficOnly is true, but the error is likely network, not protocol.
✗
The storage account does not have a firewall rule for the VM's public IP
Why it's wrong here
The rule is configured for the virtual network, not public IP.
✓
The subnet does not have a service endpoint for Microsoft.Storage enabled
Why this is correct
Virtual network rules require a service endpoint on the subnet to be effective.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The storage account uses GRS replication which is not supported with network rules
Why it's wrong here
GRS works with network rules.
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: The subnet does not have a service endpoint for Microsoft.Storage enabled — The network rule set has defaultAction set to Deny, and only virtual network rules are configured. For traffic from a VM in subnet-a to be allowed, the VM's subnet must be listed. However, the VM might not have a service endpoint enabled for Microsoft.Storage on that subnet. Option A is wrong because the subnet is listed. Option C is wrong because HTTPS is enabled. Option D is wrong because GRS does not prevent access.
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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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