Network Security Groups (NSG) in Azure - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Network Security Group (NSG) in Azure?

An NSG is like a security guard for your cloud network. It controls which traffic can enter or leave your virtual machines by using rules that allow or block traffic based on source, destination, port, and protocol.

beginner

How do NSG rules work in Azure?

NSG rules check network traffic against a list of rules in order. Each rule either allows or denies traffic based on conditions like IP address, port, and protocol. The first matching rule decides if the traffic is allowed or blocked.

beginner

What are the two main types of NSG rules?

Inbound rules control traffic coming into a resource. Outbound rules control traffic leaving a resource. Both help protect your cloud resources by filtering traffic.

intermediate

Where can you apply an NSG in Azure?

You can apply an NSG to a subnet or directly to a network interface of a virtual machine. This lets you control traffic at different levels in your network.

intermediate

Why is it important to have a default deny rule in NSGs?

A default deny rule blocks all traffic that does not match any allow rule. This ensures only traffic you explicitly allow can reach your resources, improving security by preventing unwanted access.

What does an NSG primarily control in Azure?

A User login permissions

B Storage account access

C Network traffic to and from resources

D Virtual machine size

NSGs control network traffic by allowing or blocking it based on rules.

Which of the following is NOT a condition you can use in an NSG rule?

A User password

B Destination port

C Source IP address

D Protocol type

NSG rules do not use user passwords; they filter traffic based on network parameters.

Where can you apply an NSG in Azure?

A On a storage account

B On a subnet or network interface

C On a database

D On a virtual machine's operating system

NSGs are applied to subnets or network interfaces to control traffic.

What happens if no NSG rule matches the network traffic?

A Traffic is denied by default

B Traffic is redirected

C Traffic is logged but allowed

D Traffic is allowed by default

NSGs have a default deny rule that blocks traffic not matching any allow rule.

Which type of NSG rule controls traffic leaving a resource?

A Firewall rule

B Inbound rule

C Access rule

D Outbound rule

Outbound rules control traffic leaving a resource.

Explain how Network Security Groups (NSGs) help protect Azure resources.

Think about how a security guard checks who can enter or leave a building.

Describe the difference between inbound and outbound NSG rules.

Consider traffic coming to and leaving from your house.

Practice

1. What is the primary purpose of an Azure Network Security Group (NSG)?

easy

A. To monitor application performance

B. To store data securely in Azure Blob Storage

C. To control inbound and outbound traffic to Azure resources

D. To manage user identities and access

Solution

1. Step 1: Understand NSG function

   NSGs are designed to filter network traffic to and from Azure resources.

2. Step 2: Identify correct purpose

   They do not store data, manage identities, or monitor performance.

3. Final Answer:

   To control inbound and outbound traffic to Azure resources -> Option C

4. Quick Check:

   NSG controls traffic [OK]

Hint: NSG controls network traffic, not data or users [OK]

Common Mistakes:

• Confusing NSG with storage or identity services
• Thinking NSG monitors performance
• Assuming NSG stores data

2. Which of the following is the correct way to specify a rule priority in an NSG rule?

easy

A. Priority is a string describing the rule

B. Priority is an IP address range

C. Priority is a boolean value true or false

D. Priority must be a unique integer between 100 and 4096

Solution

1. Step 1: Understand NSG rule priority format

   NSG rule priority is a unique integer between 100 and 4096 that determines rule evaluation order.

2. Step 2: Eliminate incorrect types

   Priority is not a string, boolean, or IP range.

3. Final Answer:

   Priority must be a unique integer between 100 and 4096 -> Option D

4. Quick Check:

   Priority = integer 100-4096 [OK]

Hint: Priority is a number from 100 to 4096 [OK]

Common Mistakes:

• Using strings or booleans for priority
• Confusing priority with IP ranges
• Not using unique priority numbers

3. Given this NSG rule:
Priority: 200, Direction: Inbound, Access: Deny, Source: Any, Destination: 10.0.0.4, Protocol: TCP, Port: 22
What happens when a user tries to SSH (port 22) to 10.0.0.4?

medium

A. The connection is denied

B. The connection is allowed only if from a specific IP

C. The connection is allowed

D. The connection is logged but allowed

Solution

1. Step 1: Analyze rule details

   The rule denies inbound TCP traffic on port 22 to destination 10.0.0.4 from any source.

2. Step 2: Determine effect on SSH connection

   SSH uses TCP port 22, so the connection attempt matches the deny rule and is blocked.

3. Final Answer:

   The connection is denied -> Option A

4. Quick Check:

   Deny inbound TCP port 22 = connection denied [OK]

Hint: Deny inbound on port 22 blocks SSH connections [OK]

Common Mistakes:

• Assuming 'Any' source means allow
• Confusing deny with logging
• Ignoring direction and port in rule

4. You created an NSG rule to allow inbound HTTP traffic on port 80, but the traffic is still blocked. What is the most likely cause?

medium

A. The NSG is not attached to the subnet or network interface

B. A higher priority deny rule blocks port 80 traffic

C. The source IP address is not specified

D. The protocol is set to UDP instead of TCP

Solution

1. Step 1: Check rule priority and conflicts

   NSG rules are evaluated by priority; a deny rule with higher priority can block traffic despite allow rules.

2. Step 2: Confirm rule attachment and protocol

   While attachment and protocol matter, the most common cause is a conflicting higher priority deny rule.

3. Final Answer:

   A higher priority deny rule blocks port 80 traffic -> Option B

4. Quick Check:

   Higher priority deny overrides allow [OK]

Hint: Check for higher priority deny rules first [OK]

Common Mistakes:

• Ignoring rule priority order
• Assuming NSG attachment is always correct
• Confusing protocol types

5. You want to restrict access so only a specific IP address (203.0.113.5) can access a VM on port 3389 (RDP). Which NSG rule configuration achieves this securely?

hard

A. Priority: 300, Direction: Inbound, Access: Allow, Source: 203.0.113.5, Destination: Any, Protocol: TCP, Port: 3389

B. Priority: 100, Direction: Inbound, Access: Deny, Source: Any, Destination: Any, Protocol: TCP, Port: 3389

C. Priority: 200, Direction: Inbound, Access: Allow, Source: Any, Destination: Any, Protocol: TCP, Port: 3389

D. Priority: 400, Direction: Outbound, Access: Allow, Source: 203.0.113.5, Destination: Any, Protocol: TCP, Port: 3389

Solution

1. Step 1: Allow only specific IP inbound on port 3389

   Priority: 300, Direction: Inbound, Access: Allow, Source: 203.0.113.5, Destination: Any, Protocol: TCP, Port: 3389 allows inbound TCP traffic on port 3389 only from IP 203.0.113.5, which matches the requirement.

2. Step 2: Check other options for correctness

   Priority: 100, Direction: Inbound, Access: Deny, Source: Any, Destination: Any, Protocol: TCP, Port: 3389 denies all inbound TCP 3389 traffic, blocking access. Priority: 200, Direction: Inbound, Access: Allow, Source: Any, Destination: Any, Protocol: TCP, Port: 3389 allows all sources, which is insecure. Priority: 400, Direction: Outbound, Access: Allow, Source: 203.0.113.5, Destination: Any, Protocol: TCP, Port: 3389 is outbound, irrelevant for inbound access.

3. Final Answer:

   Priority: 300, Direction: Inbound, Access: Allow, Source: 203.0.113.5, Destination: Any, Protocol: TCP, Port: 3389 -> Option A

4. Quick Check:

   Allow inbound TCP 3389 from specific IP [OK]

Hint: Allow inbound from specific IP, deny others by priority [OK]

Common Mistakes:

• Allowing all sources instead of specific IP
• Using outbound direction instead of inbound
• Denying all traffic without exception