What is Azure Virtual Network?
Azure Virtual Network (VNet) is the fundamental building block for your private network in Azure. VNet enables many types of Azure resources, such as Azure Virtual Machines (VM), to securely communicate with each other, the internet, and on-premises networks. VNet is similar to a traditional network that you'd operate in your own data center, but brings with it additional benefits of Azure's infrastructure such as scale, availability, and isolation.
- Address space: When creating a VNet, you must specify a custom private IP address space using public and private (RFC 1918) addresses. Azure assigns resources in a virtual network a private IP address from the address space that you assign. For example, if you deploy a VM in a VNet with address space, 10.0.0.0/16, the VM will be assigned a private IP like 10.0.0.4.
- Subnets: Subnets enable you to segment the virtual network into one or more sub-networks and allocate a portion of the virtual network's address space to each subnet. You can then deploy Azure resources in a specific subnet. Just like in a traditional network, subnets allow you to segment your VNet address space into segments that are appropriate for the organization's internal network. This also improves address allocation efficiency. You can secure resources within subnets using Network Security Groups. For more information, see Security groups.
- Regions: VNet is scoped to a single region/location; however, multiple virtual networks from different regions can be connected together using Virtual Network Peering.
- Subscription: VNet is scoped to a subscription. You can implement multiple virtual networks within each Azure subscription and Azure region.
As you build your network in Azure, it is important to keep in mind the following universal design principles:
- Ensure non-overlapping address spaces. Make sure your VNet address space (CIDR block) does not overlap with your organization's other network ranges.
- Your subnets should not cover the entire address space of the VNet. Plan ahead and reserve some address space for the future.
- It is recommended you have fewer large VNets than multiple small VNets. This will prevent management overhead.
- Secure your VNet's by assigning Network Security Groups (NSGs) to the subnets beneath them.
Communicate with the internet
All resources in a VNet can communicate outbound to the internet, by default. You can communicate inbound to a resource by assigning a public IP address or a public Load Balancer. You can also use public IP or public Load Balancer to manage your outbound connections. To learn more about outbound connections in Azure, see Outbound connections, Public IP addresses, and Load Balancer.
When using only an internal Standard Load Balancer, outbound connectivity is not available until you define how you want outbound connections to work with an instance-level public IP or a public Load Balancer.
Communicate between Azure resources
Azure resources communicate securely with each other in one of the following ways:
- Through a virtual network: You can deploy VMs, and several other types of Azure resources to a virtual network, such as Azure App Service Environments, the Azure Kubernetes Service (AKS), and Azure Virtual Machine Scale Sets. To view a complete list of Azure resources that you can deploy into a virtual network, see Virtual network service integration.
- Through a virtual network service endpoint: Extend your virtual network private address space and the identity of your virtual network to Azure service resources, such as Azure Storage accounts and Azure SQL databases, over a direct connection. Service endpoints allow you to secure your critical Azure service resources to only a virtual network. To learn more, see Virtual network service endpoints overview.
- Through VNet Peering: You can connect virtual networks to each other, enabling resources in either virtual network to communicate with each other, using virtual network peering. The virtual networks you connect can be in the same, or different, Azure regions. To learn more, see Virtual network peering.
Communicate with on-premises resources
You can connect your on-premises computers and networks to a virtual network using any combination of the following options:
- Point-to-site virtual private network (VPN): Established between a virtual network and a single computer in your network. Each computer that wants to establish connectivity with a virtual network must configure its connection. This connection type is great if you're just getting started with Azure, or for developers, because it requires little or no changes to your existing network. The communication between your computer and a virtual network is sent through an encrypted tunnel over the internet. To learn more, see Point-to-site VPN.
- Site-to-site VPN: Established between your on-premises VPN device and an Azure VPN Gateway that is deployed in a virtual network. This connection type enables any on-premises resource that you authorize to access a virtual network. The communication between your on-premises VPN device and an Azure VPN gateway is sent through an encrypted tunnel over the internet. To learn more, see Site-to-site VPN.
- Azure ExpressRoute: Established between your network and Azure, through an ExpressRoute partner. This connection is private. Traffic does not go over the internet. To learn more, see ExpressRoute.
Filter network traffic
You can filter network traffic between subnets using either or both of the following options:
- Security groups: Network security groups and application security groups can contain multiple inbound and outbound security rules that enable you to filter traffic to and from resources by source and destination IP address, port, and protocol. To learn more, see Network security groups or Application security groups.
- Network virtual appliances: A network virtual appliance is a VM that performs a network function, such as a firewall, WAN optimization, or other network function. To view a list of available network virtual appliances that you can deploy in a virtual network, see Azure Marketplace.
Route network traffic
Azure routes traffic between subnets, connected virtual networks, on-premises networks, and the Internet, by default. You can implement either or both of the following options to override the default routes Azure creates:
- Route tables: You can create custom route tables with routes that control where traffic is routed to for each subnet. Learn more about route tables.
- Border gateway protocol (BGP) routes: If you connect your virtual network to your on-premises network using an Azure VPN Gateway or ExpressRoute connection, you can propagate your on-premises BGP routes to your virtual networks. Learn more about using BGP with Azure VPN Gateway and ExpressRoute.
Azure VNet limits
There are certain limits around the number of Azure resources you can deploy. Most Azure networking limits are at the maximum values. However, you can increase certain networking limits as specified on the VNet limits page.
There is no charge for using Azure VNet, it is free of cost. Standard charges are applicable for resources, such as Virtual Machines (VMs) and other products. To learn more, see VNet pricing and the Azure pricing calculator.
To get started using a virtual network, create one, deploy a few VMs to it, and communicate between the VMs. To learn how, see the Create a virtual network quickstart.