Virtual Network Concepts

A virtual network (VNet) is a logical representation of a physical network that is implemented in software. Virtual networks enable you to securely and reliably connect Azure resources to each other, to the internet, and to your on-premises networks.

Key Components of a Virtual Network

Address Space: A private IP address range that you assign to your virtual network. This is typically a CIDR block (e.g., 10.0.0.0/16).
Subnets: Divisions of the virtual network's address space. Each subnet is a range within the virtual network's address space. Resources are deployed into subnets.
Network Interfaces (NICs): Virtual network interfaces that connect Azure resources, such as virtual machines, to a virtual network. Each NIC is associated with a subnet.
Route Tables: Define how network traffic is directed within your virtual network. By default, Azure provides system routes, but you can create custom route tables for more control.
Network Security Groups (NSGs): Act as a virtual firewall for your VNets to filter network traffic by allowing or denying inbound and outbound traffic to resources.
Gateways: Used for connecting your virtual network to other networks, such as your on-premises network (VPN Gateway) or other VNets (VNet-to-VNet connection).

Why Use Virtual Networks?

Isolation and Security: VNets provide a private and isolated environment for your Azure resources. NSGs allow granular control over traffic flow.
Connectivity: Easily connect resources within the VNet, to the internet, and to on-premises environments.
Scalability: Design your network topology to accommodate growth and changing requirements.
Hybrid Cloud: Seamlessly integrate your Azure resources with your existing on-premises infrastructure using VPN or ExpressRoute.

Common Scenarios

Deploying multi-tier applications in different subnets.
Connecting on-premises servers to Azure virtual machines securely.
Creating a hub-and-spoke network topology.
Segmenting networks for compliance or security reasons.

Did you know? You can peer VNets together to allow resources in different virtual networks to communicate with each other. This is a powerful way to create complex, interconnected cloud environments.

Example: Creating a Basic Virtual Network

Here's a conceptual example of how you might define a virtual network and a subnet using Azure CLI:


# Define variables
RESOURCE_GROUP="myResourceGroup"
LOCATION="eastus"
VNET_NAME="myVNet"
SUBNET_NAME="mySubnet"
ADDRESS_PREFIX="10.0.0.0/16"
SUBNET_PREFIX="10.0.0.0/24"

# Create a resource group if it doesn't exist
az group create --name $RESOURCE_GROUP --location $LOCATION

# Create the virtual network
az network vnet create \
  --resource-group $RESOURCE_GROUP \
  --name $VNET_NAME \
  --address-prefix $ADDRESS_PREFIX

# Create a subnet within the virtual network
az network vnet subnet create \
  --resource-group $RESOURCE_GROUP \
  --vnet-name $VNET_NAME \
  --name $SUBNET_NAME \
  --address-prefix $SUBNET_PREFIX