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Design security solutions for infrastructure →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the destinationAddressPrefix should be '*' instead of 'VirtualNetwork'. This is because Azure SQL databases are Platform-as-a-Service (PaaS) resources that, by default, have a public endpoint and do not reside within a virtual network; the 'VirtualNetwork' tag only covers IP addresses within the virtual network’s address space, so an NSG rule using that tag cannot match or deny internet traffic destined for the SQL database’s public endpoint. On the Microsoft Cybersecurity Architect exam, this question tests your understanding of how NSG service tags and address prefixes interact with Azure PaaS services—a common trap is assuming that all Azure resources are inside a virtual network, when in fact many PaaS services require private endpoints or service endpoints to be reachable via VNet traffic. Remember that for internet-bound or internet-originating traffic to PaaS services, the destination prefix must be '*' (all traffic) or the specific public IP range, not a virtual network tag. Memory tip: "PaaS is public by default—use a star to block from afar."

SC-100 Design security solutions for infrastructure Practice Question

This SC-100 practice question tests your understanding of design security solutions for infrastructure. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.

Exhibit

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [
    {
      "type": "Microsoft.Network/networkSecurityGroups",
      "apiVersion": "2023-09-01",
      "name": "nsg-db",
      "properties": {
        "securityRules": [
          {
            "name": "DenySQLFromInternet",
            "properties": {
              "protocol": "Tcp",
              "sourcePortRange": "*",
              "destinationPortRange": "1433",
              "sourceAddressPrefix": "Internet",
              "destinationAddressPrefix": "VirtualNetwork",
              "access": "Deny",
              "priority": 100,
              "direction": "Inbound"
            }
          }
        ]
      }
    }
  ]
}

Refer to the exhibit. The NSG is applied to a subnet containing Azure SQL databases. You notice that traffic from the internet to the databases is not being denied. 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.

Question 1mediummultiple choice
Review the full subnetting walkthrough →

Exhibit

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [
    {
      "type": "Microsoft.Network/networkSecurityGroups",
      "apiVersion": "2023-09-01",
      "name": "nsg-db",
      "properties": {
        "securityRules": [
          {
            "name": "DenySQLFromInternet",
            "properties": {
              "protocol": "Tcp",
              "sourcePortRange": "*",
              "destinationPortRange": "1433",
              "sourceAddressPrefix": "Internet",
              "destinationAddressPrefix": "VirtualNetwork",
              "access": "Deny",
              "priority": 100,
              "direction": "Inbound"
            }
          }
        ]
      }
    }
  ]
}

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The destinationAddressPrefix should be '*' instead of 'VirtualNetwork'

Option C is correct because the destinationAddressPrefix is 'VirtualNetwork', but SQL databases are not in a virtual network by default; they are PaaS services with a public endpoint. Option A is wrong because priority 100 is high. Option B is wrong because the rule explicitly denies traffic. Option D is wrong because the direction is inbound.

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 rule should be Allow to deny traffic

    Why it's wrong here

    Deny is correct for blocking.

  • ✓

    The destinationAddressPrefix should be '*' instead of 'VirtualNetwork'

    Why this is correct

    SQL databases are not in a VNet by default; use '*' to cover all destinations.

    Clue confirmation

    The clue word "most likely" in the question point toward this answer.

    Related concept

    CIDR notation defines the prefix length.

  • ✗

    The priority of the Deny rule is too low (100)

    Why it's wrong here

    Priority 100 is high; lower numbers are higher priority.

  • ✗

    The direction should be Outbound

    Why it's wrong here

    Inbound is correct for incoming traffic to the database.

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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.

What to study next

Got this wrong? Here's your next step.

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.

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FAQ

Questions learners often ask

What does this SC-100 question test?

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 destinationAddressPrefix should be '*' instead of 'VirtualNetwork' — Option C is correct because the destinationAddressPrefix is 'VirtualNetwork', but SQL databases are not in a virtual network by default; they are PaaS services with a public endpoint. Option A is wrong because priority 100 is high. Option B is wrong because the rule explicitly denies traffic. Option D is wrong because the direction is inbound.

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.

About these practice questions

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Same concept, more angles

1 more ways this is tested on SC-100

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. Refer to the exhibit. The NSG is applied to a subnet containing a web server. The web server is not receiving HTTP traffic. What is the most likely cause?

medium
  • A.The DenyAllOther rule has a lower priority than AllowHTTP
  • B.The rule direction is Inbound, but the traffic is outbound
  • ✓ C.The sourceAddressPrefix 'Internet' does not include all source IPs
  • D.The priority of the AllowHTTP rule is too low (100)

Why C: Option B is correct because the rule uses 'Internet' as sourceAddressPrefix, which is a service tag that does not include all public IPs. The actual source IPs may not be covered. Option A is wrong because priority 100 is high enough (lower number = higher priority). Option C is wrong because the rules are correct for inbound traffic. Option D is wrong because the DenyAllOther rule has a higher priority number (1000) than AllowHTTP (100), so it is evaluated after AllowHTTP.

Last reviewed: Jun 21, 2026

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