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Design security solutions for infrastructure →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the NSG rule blocks all inbound traffic from the internet to the subnet. This is correct because the rule explicitly denies any traffic sourced from the 'Internet' service tag, which represents all IP addresses originating outside of Azure, regardless of protocol or port, and applies it at the subnet level. On the Microsoft Cybersecurity Architect exam, this scenario tests your understanding of how NSG service tags interact with inbound security rules, often appearing in PowerShell or ARM template analysis questions. A common trap is assuming the rule also blocks outbound traffic or traffic from other Azure services, but it only affects inbound internet-sourced flows. Remember the memory tip: "Internet inbound is denied, but Azure internal is still alive."

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.

Exhibit

Refer to the exhibit.

$rg = 'rg-network'
$vnet = 'vnet-prod'
$subnet = 'snet-app'
$nic = 'nic-app1'
$nsg = 'nsg-app'

# Create NSG
$nsgParams = @{
    ResourceGroupName = $rg
    Name = $nsg
    Location = 'eastus'
}
$nsgObj = New-AzNetworkSecurityGroup @nsgParams

# Add rule to deny inbound from internet
$ruleParams = @{
    Name = 'DenyInternetInbound'
    Access = 'Deny'
    Priority = 100
    Direction = 'Inbound'
    Protocol = '*' 
    SourceAddressPrefix = 'Internet'
    SourcePortRange = '*'
    DestinationAddressPrefix = '*' 
    DestinationPortRange = '*'
    NetworkSecurityGroup = $nsgObj
}
Add-AzNetworkSecurityRuleConfig @ruleParams | Set-AzNetworkSecurityGroup

# Associate NSG with subnet
$vnetObj = Get-AzVirtualNetwork -ResourceGroupName $rg -Name $vnet
$subnetObj = $vnetObj.Subnets | Where-Object {$_.Name -eq $subnet}
$subnetObj.NetworkSecurityGroup = $nsgObj
Set-AzVirtualNetwork -VirtualNetwork $vnetObj

Refer to the exhibit. You are reviewing a PowerShell script that configures network security. What is the effect of the NSG rule created in this script?

Question 1mediummultiple choice
Full question →

Exhibit

Refer to the exhibit.

$rg = 'rg-network'
$vnet = 'vnet-prod'
$subnet = 'snet-app'
$nic = 'nic-app1'
$nsg = 'nsg-app'

# Create NSG
$nsgParams = @{
    ResourceGroupName = $rg
    Name = $nsg
    Location = 'eastus'
}
$nsgObj = New-AzNetworkSecurityGroup @nsgParams

# Add rule to deny inbound from internet
$ruleParams = @{
    Name = 'DenyInternetInbound'
    Access = 'Deny'
    Priority = 100
    Direction = 'Inbound'
    Protocol = '*' 
    SourceAddressPrefix = 'Internet'
    SourcePortRange = '*'
    DestinationAddressPrefix = '*' 
    DestinationPortRange = '*'
    NetworkSecurityGroup = $nsgObj
}
Add-AzNetworkSecurityRuleConfig @ruleParams | Set-AzNetworkSecurityGroup

# Associate NSG with subnet
$vnetObj = Get-AzVirtualNetwork -ResourceGroupName $rg -Name $vnet
$subnetObj = $vnetObj.Subnets | Where-Object {$_.Name -eq $subnet}
$subnetObj.NetworkSecurityGroup = $nsgObj
Set-AzVirtualNetwork -VirtualNetwork $vnetObj

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

✓

It blocks all inbound traffic from the internet to the subnet.

The rule denies all inbound traffic from the 'Internet' service tag to all ports and protocols. 'Internet' includes traffic from outside Azure. The rule is applied at the subnet level. It does not affect outbound traffic, nor traffic from other Azure services unless they originate from the internet.

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.

  • ✗

    It blocks all outbound traffic to the internet from the subnet.

    Why it's wrong here

    The rule is inbound direction, not outbound.

  • ✗

    It blocks inbound traffic only from specific IP ranges.

    Why it's wrong here

    The source is 'Internet', which is a service tag, not specific IPs.

  • ✓

    It blocks all inbound traffic from the internet to the subnet.

    Why this is correct

    The rule denies inbound from the Internet service tag to the entire subnet.

    Related concept

    CIDR notation defines the prefix length.

  • ✗

    It allows inbound traffic from the internet, then denies it.

    Why it's wrong here

    The rule is deny, not allow; there is no preceding allow rule.

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: It blocks all inbound traffic from the internet to the subnet. — The rule denies all inbound traffic from the 'Internet' service tag to all ports and protocols. 'Internet' includes traffic from outside Azure. The rule is applied at the subnet level. It does not affect outbound traffic, nor traffic from other Azure services unless they originate from the internet.

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.

About these practice questions

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Same concept, more angles

2 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. You review a PowerShell script that configures an NSG rule. What is the likely security issue with this rule?

hard
  • A.The source address prefix should be a specific IP range
  • B.The rule allows HTTPS instead of HTTP
  • C.The rule is outbound but should be inbound
  • ✓ D.The destination address prefix is 'VirtualNetwork' which allows traffic to all VMs

Why D: Option D is correct: The rule allows HTTP (port 80) from the Internet to the VirtualNetwork address prefix, which effectively allows inbound traffic from any public IP to all VMs in the virtual network on port 80. This is overly permissive. Option A is wrong because the rule allows HTTP, not HTTPS. Option B is wrong because the rule allows inbound, not outbound. Option C is wrong because the rule allows Internet, not a specific IP.

Variation 2. 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?

easy
  • A.Only inbound traffic on port 80 is denied
  • B.All inbound traffic is allowed because no default deny rule is present
  • ✓ C.Only inbound traffic from 10.0.1.0/24 on port 80 is allowed; all other inbound traffic is denied
  • D.All inbound traffic is allowed except from 10.0.1.0/24

Why C: 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.

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Last reviewed: Jun 21, 2026

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