The answer is that the script is missing the Set-AzVirtualNetwork call after updating the subnet. This is because Set-AzVirtualNetworkSubnetConfig only modifies the local in-memory representation of the subnet configuration within the virtual network object; it does not persist those changes to Azure. Without calling Set-AzVirtualNetwork to push the updated object back to the resource manager, the NSG association is never saved, so connectivity tests will show the rules are not applied. On the Microsoft Cybersecurity Architect exam, this scenario tests your understanding of the imperative Azure PowerShell workflow, where configuration changes must be explicitly committed—a common trap is assuming that Set-AzVirtualNetworkSubnetConfig alone is sufficient. A reliable memory tip is to think of it like editing a document: Set-AzVirtualNetworkSubnetConfig is typing the changes, but Set-AzVirtualNetwork is clicking "Save."
SC-100 Design security solutions for infrastructure Practice Question
This SC-100 practice question tests your understanding of design security solutions for infrastructure. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 run the PowerShell script to apply an NSG to a subnet. However, connectivity tests show that the NSG rule is not being applied. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The script is missing the Set-AzVirtualNetwork call after updating the subnet.
Option D is correct because after modifying the subnet configuration with Set-AzVirtualNetworkSubnetConfig, you must apply the changes using Set-AzVirtualNetwork to update the VNet. Without that, the NSG association is not saved. Option A is wrong because the NSG is created and associated to the subnet, but the VNet update is missing. Option B is wrong because the priority is valid. Option C is wrong because the NSG is applied to the subnet, not the NIC.
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 NSG was not associated to the subnet; Set-AzVirtualNetworkSubnetConfig does not associate the NSG.
Why it's wrong here
Set-AzVirtualNetworkSubnetConfig does associate the NSG, but the VNet must be updated.
✓
The script is missing the Set-AzVirtualNetwork call after updating the subnet.
Why this is correct
The subnet configuration is updated locally, but the VNet is not updated, so the NSG association is not persisted.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The rule priority 100 conflicts with an existing rule with lower priority.
Why it's wrong here
Lower priority numbers are evaluated first; 100 is fine.
✗
The NSG should be associated to the network interface instead of the subnet.
Why it's wrong here
Both subnet and NIC associations work; subnet association is correct for this scenario.
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.
Trap categories for this question
Scenario analysis trap
Both subnet and NIC associations work; subnet association is correct for this scenario.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this SC-100 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 SC-100 subnetting questions on CIDR, address ranges, and subnet selection.
Design security solutions for infrastructure — This question tests Design security solutions for infrastructure — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The script is missing the Set-AzVirtualNetwork call after updating the subnet. — Option D is correct because after modifying the subnet configuration with Set-AzVirtualNetworkSubnetConfig, you must apply the changes using Set-AzVirtualNetwork to update the VNet. Without that, the NSG association is not saved. Option A is wrong because the NSG is created and associated to the subnet, but the VNet update is missing. Option B is wrong because the priority is valid. Option C is wrong because the NSG is applied to the subnet, not the NIC.
What should I do if I get this SC-100 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 SC-100 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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