The correct answer is that the Key Vault is accessible only from the 10.0.0.0/24 subnet. This is because the Key Vault network ACLs default action is set to Deny, which blocks all traffic by default, but the configuration includes an IP rule that explicitly allows traffic from the 10.0.0.0/24 range. In Azure, when the defaultAction is Deny, any IP address not listed in an allow rule is automatically rejected, making the IP rule the sole exception granting access. On the SC-900 exam, this scenario tests your understanding of how network ACLs enforce perimeter security for Key Vault, often appearing as a trick where candidates mistakenly think a Deny default blocks everything, forgetting that explicit allow rules override it. A common trap is assuming public network access is still enabled, but with defaultAction: Deny, internet traffic is blocked unless a specific IP rule permits it. Memory tip: think of the defaultAction as a locked door—only the IP rules are the keys that unlock entry.
SC-900 Practice Question: Describe the capabilities of Microsoft security solutions
This SC-900 practice question tests your understanding of describe the capabilities of microsoft security solutions. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 are reviewing an ARM template for an Azure resource. Assuming the resource is a Key Vault, what is the effect of the networkAcls configuration?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Key Vault is accessible only from the 10.0.0.0/24 subnet.
The defaultAction is Deny, but an IP rule allows traffic from 10.0.0.0/24. So only that subnet can access the Key Vault. Option D is correct. Option A is wrong because public network access is disabled, so it's not accessible from the internet. Option B is wrong because the IP rule allows the subnet. Option C is wrong because the default action is Deny, not Allow.
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 Key Vault is accessible from any network.
Why it's wrong here
Incorrect: PublicNetworkAccess is Disabled and defaultAction is Deny.
✓
The Key Vault is accessible only from the 10.0.0.0/24 subnet.
Why this is correct
Correct: The IP rule allows that subnet, and default action denies all others.
The Key Vault is accessible from all Azure services.
Why it's wrong here
Incorrect: Only the specified IP range is allowed.
✗
The Key Vault is not accessible from any network.
Why it's wrong here
Incorrect: The IP rule allows traffic from 10.0.0.0/24.
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 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-900 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-900 subnetting questions on CIDR, address ranges, and subnet selection.
Describe the capabilities of Microsoft security solutions — This question tests Describe the capabilities of Microsoft security solutions — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The Key Vault is accessible only from the 10.0.0.0/24 subnet. — The defaultAction is Deny, but an IP rule allows traffic from 10.0.0.0/24. So only that subnet can access the Key Vault. Option D is correct. Option A is wrong because public network access is disabled, so it's not accessible from the internet. Option B is wrong because the IP rule allows the subnet. Option C is wrong because the default action is Deny, not Allow.
What should I do if I get this SC-900 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-900 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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