Create a network security group

In the previous tutorial, we thoroughly discussed how to create and configure virtual machines (VMs) in Microsoft Azure. In this tutorial, we’ll focus on setting up the virtual network and subnets associated with those VMs. A virtual network is a critical component of the Azure cloud—it enables logical isolation and interconnection of VMs and other resources.

What Is a Virtual Network?

A virtual network is a foundational Azure concept: it functions as a logical network where you can define IP address ranges, subnets, routing rules, and network security policies. It ensures your Azure resources communicate securely and efficiently. When creating a virtual network, consider the following key aspects:

1. IP Address Range: Define the CIDR (Classless Inter-Domain Routing) block for the entire virtual network.
2. Subnets: Partition the virtual network into multiple subnets to simplify management and resource allocation.
3. Network Security Groups (NSGs): Control inbound and outbound traffic to and from subnets.

Creating a Virtual Network

Step 1: Sign in to the Azure Portal

First, sign in to the Azure portal. Ensure you have sufficient permissions to create virtual networks.

Step 2: Create a New Virtual Network

1. In the left navigation pane of the Azure portal, select Create a resource.

2. Search for and select Virtual Network.

3. Click Create, then provide the following information:

   • Name: Enter a name for your virtual network—for example, MyVNet.
   • Address space: Specify an IP address range—for example, 10.0.0.0/16.
   • Subnet: Define a default subnet here—for example:
     • Name: MySubnet
     • Address range: 10.0.0.0/24

Select your desired Region, then complete the creation process.

Code Example

Besides using the Azure portal’s graphical interface, you can also create a virtual network via the Azure CLI. Here's an example command:

az network vnet create \
  --name MyVNet \
  --resource-group MyResourceGroup \
  --address-prefix 10.0.0.0/16 \
  --subnet-name MySubnet \
  --subnet-prefix 10.0.0.0/24

This command creates a new virtual network and subnet within the specified resource group.

Creating Subnets

To add additional subnets to an existing virtual network, follow these steps:

1. In the Azure portal, locate and select your previously created virtual network (MyVNet).

2. In the left menu of the virtual network blade, select Subnets.

3. Click + Add subnet, then fill in the following details:

   • Name: For example, MySecondSubnet
   • Address range: For example, 10.0.1.0/24

4. Click OK to save.

Code Example

Using the Azure CLI, you can add a new subnet with the following command:

az network vnet subnet create \
  --name MySecondSubnet \
  --resource-group MyResourceGroup \
  --vnet-name MyVNet \
  --address-prefix 10.0.1.0/24

Network Security Groups (NSGs)

To protect your virtual network, use Network Security Groups (NSGs) to restrict inbound and outbound traffic. NSGs can be associated with either subnets or individual VM network interfaces.

Creating and Configuring an NSG

1. In the Azure portal, select Create a resource.
2. Search for Network Security Group, then create one.
3. Provide basic information such as name and resource group.
4. After creation, select the NSG and add inbound and outbound rules—specifying priority, port(s), and protocol.

Code Example

Below is an example of how to create an NSG and add a rule using the Azure CLI:

# Create a network security group
az network nsg create \
  --resource-group MyResourceGroup \
  --name MyNSG

# Add an inbound rule
az network nsg rule create \
  --resource-group MyResourceGroup \
  --nsg-name MyNSG \
  --name AllowSSH \
  --protocol tcp \
  --priority 100 \
  --destination-port-range 22 \
  --access allow

Summary

In this tutorial, we covered how to create and configure virtual networks and subnets in Azure—and explored the fundamentals of Network Security Groups (NSGs). By following these steps, you can ensure secure and efficient communication among your VMs while maintaining flexible, business-driven network management.

In the next tutorial, we’ll explore how to use load balancers and scale sets to manage traffic across multiple VMs—ensuring high availability and dynamic scalability. Stay tuned!