An Azure virtual network (VNet) is a representation of your own network in the cloud. It is a logical isolation of the Azure cloud dedicated to your subscription. You can fully control the IP address blocks, DNS settings, security policies, and route tables within this network. You can also further segment your VNet into subnets and launch Azure IaaS virtual machines (VMs) and/or Cloud services (PaaS role instances). Additionally, you can connect the virtual network to your on-premises network using one of the connectivity options available in Azure. In essence, you can expand your network to Azure, with complete control on IP address blocks with the benefit of enterprise scale Azure provides.
The figure below shows an on-premises network connected to the public Internet through a router. You can also see a firewall between the router and a DMZ hosting a DNS server and a web server farm. The web server farm is load balanced using a hardware load balancer that is exposed to the Internet, and consumes resources from the internal subnet. The internal subnet is separated from the DMZ by another firewall, and hosts Active Directory Domain Controller servers, database servers, and application servers.
Notice how the Azure infrastructure takes on the role of the router, allowing access from your VNet to the public Internet without the need of any configuration. Firewalls can be substituted by Network Security Groups (NSGs) applied to each individual subnet. And physical load balancers are substituted by internet facing and internal load balancers in Azure.
Virtual Network Benefits
- Isolation. VNets are completely isolated from one another. That allows you to create disjoint networks for development, testing, and production that use the same CIDR address blocks.
- Access to the public Internet. All IaaS VMs and PaaS role instances in a VNet can access the public Internet by default. You can control access by using Network Security Groups (NSGs).
- Access to VMs within the VNet. PaaS role instances and IaaS VMs can be launched in the same virtual network and they can connect to each other using private IP addresses even if they are in different subnets without the need to configure a gateway or use public IP addresses.
- Name resolution. Azure provides internal name resolution for IaaS VMs and PaaS role instances deployed in your VNet. You can also deploy your own DNS servers and configure the VNet to use them.
- Security. Traffic entering and exiting the virtual machines and PaaS role instances in a VNet can be controlled using Network Security groups.
- Connectivity. VNets can be connected to each other, and even to your on-premises datacenter, by using a site-to-site VPN connection, or ExpressRoute connection. To learn more about VPN gateways, visit About VPN gateways. To learn more about ExpressRoute, visit ExpressRoute technical overview.