The answer is that the Databricks cluster is not using a managed virtual network with a service endpoint to the storage account. This is correct because when a storage account firewall is configured with a subnet rule, the default action is to deny all traffic, and only requests originating from the specified subnet are permitted. If the Databricks cluster is deployed in its own unmanaged virtual network or is not associated with that exact subnet, its traffic will be blocked even though it resides in the same overall virtual network. On the DP-203 exam, this scenario tests your understanding of how Azure Databricks networking interacts with Azure Storage firewalls—a common trap is assuming that being in the same virtual network is sufficient, when in fact the cluster must either use a managed VNet with a service endpoint or be explicitly added to the subnet rule. Remember the tip: “Same VNet ≠ same subnet; a service endpoint bridges the gap.”
DP-203 Practice Question: Secure, monitor, and optimize data storage and data processing
This DP-203 practice question tests your understanding of secure, monitor, and optimize data storage and data processing. 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 deploy the ARM template to create a storage account. After deployment, a developer reports that they cannot access the storage account from an Azure Databricks notebook running in the same virtual network as specified in the subnet rule. What is the most likely reason?
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.
The storage account uses customer-managed keys from Key Vault, which requires additional permissions.
Why wrong: CMK does not block network access; it only affects encryption.
B
The firewall default action is Deny, and there are no IP rules allowing the Databricks cluster's public IP.
Why wrong: The subnet rule should allow traffic via service endpoint; however, if Databricks cluster is not using that subnet, it will be denied.
C
The Databricks cluster is not using a managed virtual network with a service endpoint to the storage account.
For the subnet rule to work, the Databricks cluster must be deployed in a virtual network that has a service endpoint to Microsoft.Storage. If the cluster is using a public IP, access is denied.
D
The storage account has hierarchical namespace enabled, which blocks non-ADLS Gen2 tools.
Why wrong: HNS enables ADLS Gen2 features; it does not block access.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Databricks cluster is not using a managed virtual network with a service endpoint to the storage account.
Option D is correct because the default action is Deny, and only traffic from the specified subnet is allowed. The developer's Databricks notebook might be using a cluster that is not using a managed virtual network or is not in that subnet. Option A is wrong because HNS enabled does not block access. Option B is wrong because firewall is correctly set to Deny with a rule for the subnet. Option C is wrong because the key vault encryption doesn't block 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 uses customer-managed keys from Key Vault, which requires additional permissions.
Why it's wrong here
CMK does not block network access; it only affects encryption.
✗
The firewall default action is Deny, and there are no IP rules allowing the Databricks cluster's public IP.
Why it's wrong here
The subnet rule should allow traffic via service endpoint; however, if Databricks cluster is not using that subnet, it will be denied.
✓
The Databricks cluster is not using a managed virtual network with a service endpoint to the storage account.
Why this is correct
For the subnet rule to work, the Databricks cluster must be deployed in a virtual network that has a service endpoint to Microsoft.Storage. If the cluster is using a public IP, access is denied.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The storage account has hierarchical namespace enabled, which blocks non-ADLS Gen2 tools.
Why it's wrong here
HNS enables ADLS Gen2 features; it does not block access.
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 DP-203 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 DP-203 subnetting questions on CIDR, address ranges, and subnet selection.
Secure, monitor, and optimize data storage and data processing — This question tests Secure, monitor, and optimize data storage and data processing — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The Databricks cluster is not using a managed virtual network with a service endpoint to the storage account. — Option D is correct because the default action is Deny, and only traffic from the specified subnet is allowed. The developer's Databricks notebook might be using a cluster that is not using a managed virtual network or is not in that subnet. Option A is wrong because HNS enabled does not block access. Option B is wrong because firewall is correctly set to Deny with a rule for the subnet. Option C is wrong because the key vault encryption doesn't block access.
What should I do if I get this DP-203 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 DP-203 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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