Create a Subnet in an Azure Virtual Network

This guide provides step-by-step instructions on how to create a new subnet within an existing Azure Virtual Network (VNet) using the Azure portal, Azure CLI, and Azure PowerShell.

Prerequisites

• An existing Azure Virtual Network. If you don't have one, you can create a VNet first.
• Appropriate permissions to manage virtual networks in your Azure subscription.

Method 1: Using the Azure Portal

1. Sign in to the Azure portal: Go to https://portal.azure.com/ and sign in with your Azure account.
2. Navigate to your Virtual Network: Search for "Virtual networks" in the search bar at the top and select "Virtual networks" from the results. Click on the name of the virtual network you want to add a subnet to.
3. Access Subnets: In the virtual network's overview page, select Subnets from the left-hand menu under "Settings".
4. Add Subnet: Click the + Subnet button at the top of the subnets list.
5. Configure Subnet Details:
   • Name: Enter a unique name for your subnet (e.g., WebServersSubnet, AppTierSubnet).
   • Address range: Specify a valid IPv4 address range in CIDR notation that is a subset of the VNet's address space (e.g., 10.0.2.0/24). Ensure this range does not overlap with existing subnets.
   • Network Security Group: (Optional) Choose an existing Network Security Group (NSG) or create a new one to apply network security rules. Select "None" if you don't want to associate an NSG at this time.
   • Route Table: (Optional) Choose an existing route table or create a new one for custom routing. Select "None" if you don't want to associate a route table.
   • Service endpoints: (Optional) Enable service endpoints for specific Azure services if needed.
   • Private endpoints: (Optional) Configure private endpoint connections.
   • Enable DDoS protection: (Optional) Enable Azure DDoS Protection Standard for enhanced protection.
   • Enable subnet private link service: (Optional) Enable for private link service.
6. Save: Click the Save button at the bottom to create the subnet.

Method 2: Using Azure CLI

Follow these steps to create a subnet using the Azure Command-Line Interface.

1. Install and configure Azure CLI: Ensure you have Azure CLI installed and are logged in to your Azure account using az login.
2. Create the subnet: Use the following command, replacing the placeholders with your actual values:

az network vnet subnet create \
  --resource-group <your-resource-group-name> \
  --vnet-name <your-vnet-name> \
  --name <your-subnet-name> \
  --address-prefixes <your-subnet-address-range> \
  --network-security-group <your-nsg-name-optional> \
  --route-table <your-route-table-name-optional>

Example:

az network vnet subnet create \
  --resource-group MyResourceGroup \
  --vnet-name MyVNet \
  --name WebServersSubnet \
  --address-prefixes 10.0.2.0/24

Method 3: Using Azure PowerShell

Follow these steps to create a subnet using Azure PowerShell.

1. Install and configure Azure PowerShell: Ensure you have the Azure PowerShell module installed and are connected to your Azure account using Connect-AzAccount.
2. Retrieve the virtual network object:

$vnet = Get-AzVirtualNetwork -ResourceGroupName "<your-resource-group-name>" -Name "<your-vnet-name>"

Define the subnet configuration:

$subnet = New-AzVirtualNetworkSubnetConfig -Name "<your-subnet-name>" -AddressPrefix "<your-subnet-address-range>"

Add the subnet to the virtual network and update:

$vnet | Add-AzVirtualNetworkSubnetConfig -Name $subnet.Name -AddressPrefix $subnet.AddressPrefix
$vnet | Set-AzVirtualNetwork

Example:

$vnet = Get-AzVirtualNetwork -ResourceGroupName "MyResourceGroup" -Name "MyVNet"
$subnet = New-AzVirtualNetworkSubnetConfig -Name "AppTierSubnet" -AddressPrefix "10.0.3.0/24"
$vnet | Add-AzVirtualNetworkSubnetConfig -Name $subnet.Name -AddressPrefix $subnet.AddressPrefix
$vnet | Set-AzVirtualNetwork

Next Steps

• Configure Network Security Groups for your subnet
• Learn about IP addressing in Azure
• Create and manage route tables