IP address types and allocation methods in Azure
You can assign IP addresses to Azure resources to communicate with other Azure resources, your on-premises network, and the Internet. There are two types of IP addresses you can use in Azure:
- Public IP addresses: Used for communication with the Internet, including Azure public-facing services.
- Private IP addresses: Used for communication within an Azure virtual network (VNet), and your on-premises network, when you use a VPN gateway or ExpressRoute circuit to extend your network to Azure.
Azure has two different deployment models for creating and working with resources: Resource Manager and classic. This article covers using the Resource Manager deployment model, which Microsoft recommends for most new deployments instead of the classic deployment model.
If you are familiar with the classic deployment model, check the differences in IP addressing between classic and Resource Manager.
Public IP addresses
Public IP addresses allow Internet resources to communicate inbound to Azure resources. Public IP addresses also enable Azure resources to communicate outbound to Internet and public-facing Azure services with an IP address assigned to the resource. The address is dedicated to the resource, until it is unassigned by you. If a public IP address is not assigned to a resource, the resource can still communicate outbound to the Internet, but Azure dynamically assigns an available IP address that is not dedicated to the resource. For more information about outbound connections in Azure, see Understand outbound connections.
In Azure Resource Manager, a public IP address is a resource that has its own properties. Some of the resources you can associate a public IP address resource with are:
- Virtual machine network interfaces
- Internet-facing load balancers
- VPN gateways
- Application gateways
IP address version
Public IP addresses are created with an IPv4 or IPv6 address. Public IPv6 addresses can only be assigned to Internet-facing load balancers.
Public IP addresses are created with one of the following SKUs:
Matching SKUs must be used for load balancer and public IP resources. You can't have a mixture of basic SKU resources and standard SKU resources. You can't attach standalone virtual machines, virtual machines in an availability set resource, or a virtual machine scale set resources to both SKUs simultaneously. New designs should consider using Standard SKU resources. Please review Standard Load Balancer for details.
All public IP addresses created before the introduction of SKUs are Basic SKU public IP addresses. With the introduction of SKUs, you have the option to specify which SKU you would like the public IP address to be. Basic SKU addresses are:
- Assigned with the static or dynamic allocation method.
- Are open by default. Network security groups are recommended but optional for restricting inbound or outbound traffic.
- Assigned to any Azure resource that can be assigned a public IP address, such as network interfaces, VPN Gateways, Application Gateways, and Internet-facing load balancers.
- Can be assigned to a specific zone.
- Not zone redundant. To learn more about availability zones, see Availability zones overview.
Standard SKU public IP addresses are:
- Assigned with the static allocation method only.
- Are secure by default and closed to inbound traffic. You must explicit whitelist allowed inbound traffic with a network security group.
- Assigned to network interfaces or public standard load balancers. For more information about Azure standard load balancers, see Azure standard load balancer.
- Zone redundant by default. Can be created zonal and guaranteed in a specific availability zone. To learn more about availability zones, see Availability zones overview and Standard Load Balancer and Availability Zones.
Communication with a standard SKU resource fails until you create and associate a network security group and explicitly allow the desired inbound traffic.
Both basic and standard SKU public IP addresses support the static allocation method. The resource is assigned an IP address at the time it is created and the IP address is released when the resource is deleted.
Basic SKU public IP addresses also support a dynamic allocation method, which is the default if allocation method is not specified. Selecting dynamic allocation method for a basic public IP address resource means the IP address is not allocated at the time of the resource creation. The public IP address is allocated when you associate the public IP address with a virtual machine or when you place the first virtual machine instance into the backend pool of a basic load balancer. The IP address is released when you stop (or delete) the resource. After being released from resource A, for example, the IP address can be assigned to a different resource. If the IP address is assigned to a different resource while resource A is stopped, when you restart resource A, a different IP address is assigned. If you change the allocation method of a basic public IP address resource from static to dynamic, the address is released. To ensure the IP address for the associated resource remains the same, you can set the allocation method explicitly to static. A static IP address is assigned immediately.
Even when you set the allocation method to static, you cannot specify the actual IP address assigned to the public IP address resource. Azure assigns the IP address from a pool of available IP addresses in the Azure location the resource is created in.
Static public IP addresses are commonly used in the following scenarios:
- When you must update firewall rules to communicate with your Azure resources.
- DNS name resolution, where a change in IP address would require updating A records.
- Your Azure resources communicate with other apps or services that use an IP address-based security model.
- You use SSL certificates linked to an IP address.
Azure allocates public IP addresses from a range unique to each Azure region. For details, see Azure Datacenter IP ranges.
DNS hostname resolution
You can specify a DNS domain name label for a public IP resource, which creates a mapping for domainnamelabel.location.cloudapp.azure.com to the public IP address in the Azure-managed DNS servers. For instance, if you create a public IP resource with contoso as a domainnamelabel in the West US Azure location, the fully qualified domain name (FQDN) contoso.westus.cloudapp.azure.com resolves to the public IP address of the resource. You can use the FQDN to create a custom domain CNAME record pointing to the public IP address in Azure. Instead of, or in addition to, using the DNS name label with the default suffix, you can use the Azure DNS service to configure a DNS name with a custom suffix that resolves to the public IP address. For more information, see Use Azure DNS with an Azure public IP address.
Each domain name label created must be unique within its Azure location.
You can associate a public IP address with a Windows or Linux virtual machine by assigning it to its network interface. You can assign either a dynamic or a static public IP address to a virtual machine. Learn more about assigning IP addresses to network interfaces.
Internet-facing load balancers
You can associate a public IP address created with either SKU with an Azure Load Balancer, by assigning it to the load balancer frontend configuration. The public IP address serves as a load-balanced virtual IP address (VIP). You can assign either a dynamic or a static public IP address to a load balancer front-end. You can also assign multiple public IP addresses to a load balancer front-end, which enables multi-VIP scenarios like a multi-tenant environment with SSL-based websites. For more information about Azure load balancer SKUs, see Azure load balancer standard SKU.
An Azure VPN Gateway connects an Azure virtual network to other Azure virtual networks, or to an on-premises network. A public IP address is assigned to the VPN Gateway to enable it to communicate with the remote network. You can only assign a dynamic basic public IP address to a VPN gateway.
You can associate a public IP address with an Azure Application Gateway, by assigning it to the gateway's frontend configuration. This public IP address serves as a load-balanced VIP. You can only assign a dynamic basic public IP address to an application gateway frontend configuration.
The following table shows the specific property through which a public IP address can be associated to a top-level resource, and the possible allocation methods (dynamic or static) that can be used.
|Top-level resource||IP Address association||Dynamic||Static|
|Virtual machine||Network interface||Yes||Yes|
|Internet-facing Load balancer||Front-end configuration||Yes||Yes|
|VPN gateway||Gateway IP configuration||Yes||No|
|Application gateway||Front-end configuration||Yes||No|
Private IP addresses
Private IP addresses allow Azure resources to communicate with other resources in a virtual network or an on-premises network through a VPN gateway or ExpressRoute circuit, without using an Internet-reachable IP address.
In the Azure Resource Manager deployment model, a private IP address is associated to the following types of Azure resources:
- Virtual machine network interfaces
- Internal load balancers (ILBs)
- Application gateways
IP address version
Private IP addresses are created with an IPv4 or IPv6 address. Private IPv6 addresses can only be assigned with the dynamic allocation method. You cannot communicate between private IPv6 addresses on a virtual network. You can communicate inbound to a private IPv6 address from the Internet, through an Internet-facing load balancer. See Create an Internet-facing load balancer with IPv6 for details.
A private IP address is allocated from the address range of the virtual network subnet a resource is deployed in. Azure reserves the first four addresses in each subnet address range, so the addresses cannot be assigned to resources. For example, if the subnet's address range is 10.0.0.0/16, addresses 10.0.0.0-10.0.0.3 cannot be assigned to resources. IP addresses within the subnet's address range can only be assigned to one resource at a time.
There are two methods in which a private IP address is allocated:
- Dynamic: Azure assigns the next available unassigned or unreserved IP address in the subnet's address range. For example, Azure assigns 10.0.0.10 to a new resource, if addresses 10.0.0.4-10.0.0.9 are already assigned to other resources. Dynamic is the default allocation method. Once assigned, dynamic IP addresses are only released if a network interface is deleted, assigned to a different subnet within the same virtual network, or the allocation method is changed to static, and a different IP address is specified. By default, Azure assigns the previous dynamically assigned address as the static address when you change the allocation method from dynamic to static.
- Static: You select and assign any unassigned or unreserved IP address in the subnet's address range. For example, if a subnet's address range is 10.0.0.0/16 and addresses 10.0.0.4-10.0.0.9 are already assigned to other resources, you can assign any address between 10.0.0.10 - 10.0.255.254. Static addresses are only released if a network interface is deleted. If you change the allocation method to dynamic, Azure dynamically assigns the previously assigned static IP address as the dynamic address, even if the address isn't the next available address in the subnet's address range. The address also changes if the network interface is assigned to a different subnet within the same virtual network, but to assign the network interface to a different subnet, you must first change the allocation method from static to dynamic. Once you've assigned the network interface to a different subnet, you can change the allocation method back to static, and assign an IP address from the new subnet's address range.
One or more private IP addresses are assigned to one or more network interfaces of a Windows or Linux virtual machine. You can specify the allocation method as either dynamic or static for each private IP address.
Internal DNS hostname resolution (for virtual machines)
All Azure virtual machines are configured with Azure-managed DNS servers by default, unless you explicitly configure custom DNS servers. These DNS servers provide internal name resolution for virtual machines that reside within the same virtual network.
When you create a virtual machine, a mapping for the hostname to its private IP address is added to the Azure-managed DNS servers. If a virtual machine has multiple network interfaces, or multiple IP configurations for a network interface the hostname is mapped to the private IP address of the primary IP configuration of the primary network interface.
Virtual machines configured with Azure-managed DNS servers are able to resolve the hostnames of all virtual machines within the same virtual network to their private IP addresses. To resolve host names of virtual machines in connected virtual networks, you must use a custom DNS server.
Internal load balancers (ILB) & Application gateways
You can assign a private IP address to the front-end configuration of an Azure Internal Load Balancer (ILB) or an Azure Application Gateway. This private IP address serves as an internal endpoint, accessible only to the resources within its virtual network and the remote networks connected to the virtual network. You can assign either a dynamic or static private IP address to the front-end configuration.
The following table shows the specific property through which a private IP address can be associated to a top-level resource, and the possible allocation methods (dynamic or static) that can be used.
|Top-level resource||IP address association||Dynamic||Static|
|Virtual machine||Network interface||Yes||Yes|
|Load balancer||Front-end configuration||Yes||Yes|
|Application gateway||Front-end configuration||Yes||Yes|
The limits imposed on IP addressing are indicated in the full set of limits for networking in Azure. The limits are per region and per subscription. You can contact support to increase the default limits up to the maximum limits based on your business needs.
Public IP addresses may have a nominal charge. To learn more about IP address pricing in Azure, review the IP address pricing page.