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Design security solutions for infrastructure →easyMultiple ChoiceObjective-mapped

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": "2021-02-01",
      "name": "nsg-backend",
      "location": "[resourceGroup().location]",
      "properties": {
        "securityRules": [
          {
            "name": "DenyAllInbound",
            "properties": {
              "protocol": "*",
              "sourcePortRange": "*",
              "destinationPortRange": "*",
              "sourceAddressPrefix": "*",
              "destinationAddressPrefix": "*",
              "access": "Deny",
              "priority": 1000,
              "direction": "Inbound"
            }
          },
          {
            "name": "AllowHTTPFromFrontend",
            "properties": {
              "protocol": "Tcp",
              "sourcePortRange": "*",
              "destinationPortRange": "80",
              "sourceAddressPrefix": "10.0.1.0/24",
              "destinationAddressPrefix": "*",
              "access": "Allow",
              "priority": 100,
              "direction": "Inbound"
            }
          }
        ]
      }
    }
  ]
}

Refer to the exhibit. You are deploying an ARM template that creates a network security group (NSG) named nsg-backend. What is the effect of this NSG on inbound traffic?

Question 1easymultiple choice
Full question →

Exhibit

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [
    {
      "type": "Microsoft.Network/networkSecurityGroups",
      "apiVersion": "2021-02-01",
      "name": "nsg-backend",
      "location": "[resourceGroup().location]",
      "properties": {
        "securityRules": [
          {
            "name": "DenyAllInbound",
            "properties": {
              "protocol": "*",
              "sourcePortRange": "*",
              "destinationPortRange": "*",
              "sourceAddressPrefix": "*",
              "destinationAddressPrefix": "*",
              "access": "Deny",
              "priority": 1000,
              "direction": "Inbound"
            }
          },
          {
            "name": "AllowHTTPFromFrontend",
            "properties": {
              "protocol": "Tcp",
              "sourcePortRange": "*",
              "destinationPortRange": "80",
              "sourceAddressPrefix": "10.0.1.0/24",
              "destinationAddressPrefix": "*",
              "access": "Allow",
              "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

✓

Only inbound traffic from 10.0.1.0/24 on port 80 is allowed; all other inbound traffic is denied

Option B is correct. The NSG has two rules: AllowHTTPFromFrontend with priority 100 allows TCP 80 from 10.0.1.0/24, and DenyAllInbound with priority 1000 denies all other inbound traffic. Since the allow rule has a higher priority (lower number), traffic from the frontend subnet on port 80 is allowed, and all other inbound traffic is denied. Option A is wrong because traffic from 10.0.1.0/24 on port 80 is allowed. Option C is wrong because the explicit deny rule exists. Option D is wrong because the deny rule is not the only 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.

  • ✗

    Only inbound traffic on port 80 is denied

    Why it's wrong here

    Port 80 from the frontend is allowed.

  • ✗

    All inbound traffic is allowed because no default deny rule is present

    Why it's wrong here

    There is an explicit deny rule with priority 1000.

  • ✓

    Only inbound traffic from 10.0.1.0/24 on port 80 is allowed; all other inbound traffic is denied

    Why this is correct

    The allow rule permits specific traffic, and the deny rule blocks everything else.

    Related concept

    CIDR notation defines the prefix length.

  • ✗

    All inbound traffic is allowed except from 10.0.1.0/24

    Why it's wrong here

    Traffic from 10.0.1.0/24 on port 80 is allowed.

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: Only inbound traffic from 10.0.1.0/24 on port 80 is allowed; all other inbound traffic is denied — Option B is correct. The NSG has two rules: AllowHTTPFromFrontend with priority 100 allows TCP 80 from 10.0.1.0/24, and DenyAllInbound with priority 1000 denies all other inbound traffic. Since the allow rule has a higher priority (lower number), traffic from the frontend subnet on port 80 is allowed, and all other inbound traffic is denied. Option A is wrong because traffic from 10.0.1.0/24 on port 80 is allowed. Option C is wrong because the explicit deny rule exists. Option D is wrong because the deny rule is not the only 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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Last reviewed: Jun 21, 2026

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