NSG in Azure: The Simplest, Beginner-Friendly Explanation

Last Update: December 8, 2025 Post Views: 1078

A simple, friendly, and complete guide to understanding Network Security Groups (NSG) in Azure using real examples.

NSG in Azure – Simple Explanation, Best Guide for Beginners | Azure Networking

NSG in Azure: The Simplest, Beginner-Friendly Explanation 


You are working in the Company. You have the Company Salary Website Hosted on Azure Cloud 

Everything is working fine… until one day, you receive multiple alerts:

  • Someone from another country is trying to connect to your server
  • Random IPs are sending RDP login attempts
  • Your VM's CPU suddenly spikes

You think:
“But only my office staff should access this server. Why is the whole world hitting it?”

This is where the Network Security Group (NSG) becomes critical.


What is NSG in Azure?

NSG stands for Network Security Group. It is like a security guard standing at the door of your Azure Virtual Machine .

Just like a security guard checks:

  • Who can enter
  • Who cannot enter
  • Who can exit
  • Who cannot exit

NSG decides what traffic can go IN and OUT of your Azure resources.


Why is NSG used in Azure?

NSG is used to increase the security of your cloud environment. In the cloud, your VM is directly accessible from the internet, so you need a gatekeeper.

NSG helps you:

  • Allow required traffic (e.g., RDP 3389, SSH 22)
  • Block unwanted traffic
  • Control communication between subnets
  • Protect VMs from hacking attempts

NSG keeps your Azure environment safe and controlled.


How Does NSG Work?

NSG works using rules. Each rule decides whether traffic should be ALLOWED or DENIED.

✔ Types of NSG Rules

  • Inbound rules – Control traffic coming from outside
  • Outbound rules – Control traffic going out from VM

✔ Rule Decision is Based On:

  • Source (Who is coming?)
  • Destination (Where are they going?)
  • Port number (Which Service?)
  • Protocol (TCP/UDP)
  • Action (Allow or Deny)
  • Priority (Lower number = higher priority)

 NSG checks every packet and decides: “Allow this” or “Block this.”


Real-Life Example of NSG

Imagine you live in a building with a security guard. You give instructions:

  • Family members – allow
  • Delivery boy – allow
  • Strangers – block
  • Late-night unknown visitor – block

Similarly, you give NSG instructions:

  • Port 3389 (RDP) – allow only from office IP
  • Port 80 (HTTP) – allow from the internet
  • All other traffic – deny

NSG behaves like a digital security guard.


Key Features of Azure NSG

  • Easy to configure
  • Inbound & outbound control
  • Works at the VM NIC and subnet level
  • Has default security rules
  • Supports service tags
  • Can create custom rules
  • Lightweight and free

NSG is simple but powerful for network protection.


Where Can You Use NSG?

✔ Common Use Cases

  • Protecting Azure Virtual Machines
  • Securing Subnets inside a Virtual Network
  • Allowing traffic only from known IPs
  • Blocking unsafe ports 

Summary: Use NSG anywhere you need simple network-level protection.


FAQs – Frequently Asked Questions

What is NSG in one sentence?

NSG is a security filter that controls inbound and outbound traffic in Azure.

Is NSG free in Azure?

Yes, NSG is completely free.

Where should I apply NSG?

On VM NIC or on subnets — both options work.


Conclusion

NSG is one of the most important security features in Azure. If you are learning Azure, mastering NSG is your first step towards cloud security.


KEY TAKEAWAY:
NSG = Your cloud security guard. It protects VMs and subnets by allowing only safe traffic and blocking all other traffic.


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