The answer is Network Security Groups (NSGs). NSGs filter network traffic to and from Azure resources using rules based on source, destination, port, and protocol, acting as a distributed, stateful firewall that evaluates each packet at the subnet or network interface level. On the Microsoft Azure Fundamentals AZ-900 exam, this question tests your understanding of how NSGs provide granular traffic control within a virtual network, often contrasting them with Azure Firewall, which is a centralized, managed service for broader network protection. A common trap is confusing NSGs with Azure Firewall—remember that NSGs are rule-based filters applied directly to subnets or NICs, while Azure Firewall is a full, cloud-native firewall service. For a memory tip, think of NSGs as the "front door bouncer" for your Azure resources: they check every packet’s source, destination, port, and protocol against a list of allowed or denied guests before letting it in or out.
AZ-900 Describe Azure architecture and services Practice Question
This AZ-900 practice question tests your understanding of describe azure architecture and services. 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.
Which Azure network security service filters network traffic to and from Azure resources using rules based on source, destination, port, and protocol?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Network Security Groups (NSGs)
Network Security Groups (NSGs) are the correct answer because they filter network traffic to and from Azure resources at the subnet or network interface level using rules that specify source, destination, port, and protocol. NSGs operate as a distributed, stateful firewall that evaluates each packet against a set of allow or deny rules, making them the primary tool for granular network traffic control within a virtual network.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Azure Firewall
Why it's wrong here
Azure Firewall is a managed, cloud-based network security service with more advanced features; NSGs provide basic traffic filtering.
✗
Azure DDoS Protection
Why it's wrong here
DDoS Protection defends against denial of service attacks, not general traffic filtering.
✓
Network Security Groups (NSGs)
Why this is correct
NSGs filter network traffic using configurable rules based on source, destination, port, and protocol.
Related concept
Read the scenario before looking for a memorised answer.
✗
Azure WAF
Why it's wrong here
WAF protects web applications from layer 7 attacks; NSGs provide network layer traffic filtering.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Azure Firewall with NSGs because both perform filtering, but Azure Firewall is a centralized, managed service for advanced scenarios (e.g., inspecting outbound traffic to the internet), while NSGs are the correct answer for basic, rule-based filtering at the resource or subnet level.
Detailed technical explanation
How to think about this question
NSGs contain a set of security rules that are evaluated in priority order (lowest number first) and are stateful, meaning that if an inbound rule allows traffic, the outbound response is automatically allowed regardless of outbound rules. Each rule includes properties such as source and destination IP address ranges (or service tags like 'VirtualNetwork'), port ranges, protocol (TCP, UDP, or Any), and an action (Allow or Deny). In a real-world scenario, an NSG might be applied to a subnet hosting a web server to allow inbound HTTP (TCP 80) and HTTPS (TCP 443) traffic from the internet while denying all other inbound traffic, ensuring only legitimate web traffic reaches the server.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-900 question in full detail.
Describe Azure architecture and services — This question tests Describe Azure architecture and services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Network Security Groups (NSGs) — Network Security Groups (NSGs) are the correct answer because they filter network traffic to and from Azure resources at the subnet or network interface level using rules that specify source, destination, port, and protocol. NSGs operate as a distributed, stateful firewall that evaluates each packet against a set of allow or deny rules, making them the primary tool for granular network traffic control within a virtual network.
What should I do if I get this AZ-900 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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