Azure Virtual Network easily extends your on-premises network through site-to-site VPN, much the way you’d set up and connect to a remote branch office. You control the network topology, including configuration of DNS and IP address ranges, and manage it just like your on-premises infrastructure.
With Virtual Network, you can build hybrid cloud applications that securely connect to your on-site datacenter—so an Azure web application can access an on-premises SQL Server database or authenticate users against an on-premises Active Directory service.
Because Virtual Network creates a direct connection between your local development machine and Azure Virtual Machines, you can troubleshoot and debug them using the same tools you would use for on-premises applications.
Virtual Networks provides an added layer of security. Only virtual machines and services within the same virtual network can identify or connect to each other. Cloud services and virtual machines on a virtual network also avoid the public internet.
With virtual networks, you can build services that rely on Cloud Services and Virtual Machines. Use Azure web roles for your front end and Virtual Machines for backend databases. Combining Platform-as-a-Service (PaaS) and Infrastructure-as-a-Service (IaaS) within a Virtual Network gives you more flexibility and scalability in building apps.