Azure NSG vs Azure Firewall: When to Use Each

Introduction #

Azure Network Security Groups and Azure Firewall are both used to control traffic, but they solve different problems.

Many beginners see both services and assume they are interchangeable. They are not. An NSG is a packet-filtering control attached close to network interfaces or subnets, while Azure Firewall is a managed security service designed for centralized inspection and policy enforcement.

Knowing where each one fits helps you avoid overengineering small environments and under-securing larger ones.

What an NSG Does #

An NSG is a layer of allow and deny rules applied to:

• A subnet
• A network interface

The rules evaluate source, destination, port, and protocol. This makes NSGs useful for segmenting traffic inside a virtual network and limiting which systems can talk to each other.

For example, you might use an NSG to:

• Allow HTTPS to a web subnet
• Allow RDP only from a management subnet
• Block direct database access from the internet

NSGs are simple, lightweight, and usually one of the first controls added in an Azure network.

What Azure Firewall Does #

Azure Firewall is a managed, stateful network security service that sits in a central location and inspects traffic flowing through it.

It supports:

• Network rules
• Application rules
• DNAT rules
• Threat intelligence filtering
• Centralized logging and policy management

This makes it more suitable when you want one place to control outbound internet access, inspect traffic across multiple spokes, or apply shared security policy across subscriptions and environments.

The Simplest Way to Think About the Difference #

A useful mental model is:

• NSG = local traffic guardrail
• Azure Firewall = centralized traffic control point

An NSG is usually attached close to the workload. Azure Firewall is usually placed in a hub or shared security boundary where traffic is intentionally routed through it.

When NSG Is Usually Enough #

An NSG is often enough when:

• The environment is small
• You mainly need subnet-level segmentation
• Outbound internet control is not very complex
• You do not need advanced application-aware filtering

For a small lab, a simple internal app, or a tightly scoped workload, NSGs can provide strong value without adding much operational overhead.

When Azure Firewall Becomes Worth It #

Azure Firewall becomes more useful when:

• Many workloads need a common egress path
• You want centralized outbound filtering
• Multiple VNets or spokes need shared policy
• Security teams need one place to review and manage rules
• You want better visibility into allowed and denied traffic

In larger environments, centralized control matters just as much as the rules themselves.

When to Use Both Together #

In real environments, the answer is often both.

You can use:

• NSGs for local segmentation at subnet or NIC level
• Azure Firewall for centralized ingress, egress, and cross-network policy

That combination gives you defense in depth. If one layer is too broad, the other can still reduce blast radius.

Common Mistake to Avoid #

One common mistake is using only NSGs and expecting them to behave like a centralized firewall platform. Another is deploying Azure Firewall everywhere when simple segmentation would have solved the problem.

Pick the control based on the design goal:

• Need local traffic restriction close to workloads? Start with NSGs.
• Need shared inspection and policy across environments? Bring in Azure Firewall.

Conclusion #

Azure NSG and Azure Firewall are complementary, not competing, services.

NSGs are best for distributed segmentation close to workloads. Azure Firewall is better for centralized inspection and policy enforcement. Once that distinction is clear, network design decisions become much easier.