The answer is to add a virtual network rule for the specific VNet. This is correct because Azure Storage firewalls operate on a default-deny model; when public network access is disabled, no traffic is allowed unless an explicit rule grants access. A virtual network rule, combined with a service endpoint on the subnet, tells the storage account to accept traffic only from that specific VNet, effectively restricting storage account access to that network boundary. On the Microsoft Cybersecurity Architect exam, this scenario tests your understanding of network segmentation controls—a common trap is thinking a service endpoint alone is sufficient, but the endpoint merely enables the route; the rule is what enforces the filter. Remember the memory tip: “Endpoint enables, rule restricts.”
SC-100 Design security solutions for infrastructure Practice Question
This SC-100 practice question tests your understanding of design security solutions for infrastructure. 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 need to ensure that the storage account 'seccorpstorage' is only accessible from a specific Azure virtual network. What should you do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a virtual network rule for the specific VNet
Option B is correct because you need to add a virtual network rule to allow traffic from the VNet. The current configuration has no rules, so all traffic is denied. Option A is wrong because the storage account already has public network access disabled. Option C is wrong because enabling firewall and adding IP rules would allow specific IPs, not a VNet. Option D is wrong because adding a service endpoint alone is incomplete without the rule.
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.
✓
Add a virtual network rule for the specific VNet
Why this is correct
Adding a VNet rule allows traffic from that VNet while blocking all other traffic.
Enable the service endpoint for Microsoft.Storage on the VNet subnet
Why it's wrong here
Service endpoint alone does not grant access; a VNet rule is also required.
✗
Enable firewall and add an IP rule for the VNet's public IP
Why it's wrong here
VNet traffic originates from private IPs, not public IPs.
✗
Enable public network access and add a firewall rule
Why it's wrong here
Public network access is already disabled; enabling it would be insecure.
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 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: Add a virtual network rule for the specific VNet — Option B is correct because you need to add a virtual network rule to allow traffic from the VNet. The current configuration has no rules, so all traffic is denied. Option A is wrong because the storage account already has public network access disabled. Option C is wrong because enabling firewall and adding IP rules would allow specific IPs, not a VNet. Option D is wrong because adding a service endpoint alone is incomplete without the rule.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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