Azure Virtual Network (VNet)

Azure Virtual Network (VNet) is a foundational networking service in Microsoft Azure that enables you to create and manage private, isolated networks in the cloud. Azure Virtual Network allows you to establish secure and seamless communication between Azure resources, on-premises resources, and the internet.

Here are the key points to understand about Azure Virtual Network:

1. **Isolation and Segmentation:** Azure Virtual Network provides network isolation, allowing you to create multiple VNets to segregate resources based on different application tiers, departments, or projects. Each VNet has its own private IP address space, which is isolated from other VNets and the internet.

2. **Private IP Address Space:** When you create a VNet, you define its private IP address space (CIDR block), which represents the range of IP addresses that can be used within the VNet. VMs and other resources deployed within the VNet are assigned private IP addresses from this address space.

3. **Subnets:** Within a VNet, you can further segment the IP address space into multiple subnets. Subnets allow you to logically group resources based on specific network requirements and security considerations. Resources within the same subnet can communicate with each other directly.

4. **Connectivity Options:**

   - **VNet-to-VNet Connectivity:** Azure VNets can be peered together to enable communication between resources in different VNets as if they were on the same network.

   - **Site-to-Site VPN:** You can establish a secure connection between an on-premises network and an Azure VNet using a site-to-site VPN. This allows resources in the VNet to communicate with resources on the on-premises network.

   - **ExpressRoute:** Azure ExpressRoute provides a private, dedicated connection between your on-premises network and Azure VNets, offering higher reliability, lower latency, and higher data transfer rates compared to VPN connections.

5. **Network Security Groups (NSGs):** NSGs are used to control inbound and outbound network traffic to and from resources within a VNet. NSGs act as basic firewalls, allowing you to define rules to permit or deny specific types of traffic.

6. **Azure Firewall and Network Virtual Appliances:** You can deploy Azure Firewall or third-party network virtual appliances within a VNet to provide advanced network security and routing capabilities.

7. **Azure DNS:** Azure Virtual Network integrates with Azure DNS, allowing you to create custom domain names and map them to private IP addresses within your VNets.

8. **Service Endpoints:** VNets can be configured with service endpoints, allowing resources within the VNet to access specific Azure services (e.g., Azure Storage or Azure SQL Database) directly without using public internet access.

Azure Virtual Network is a fundamental building block for organizing and securing your Azure resources. By using VNets, you can create private and secure networks for your applications, enabling seamless communication and connectivity between resources while maintaining control over network traffic and security.