Unlocking Azure Network Potential: Subnet Delegation Explained

Azure Virtual Network is a powerful tool that allows you to create and manage your virtual network in the cloud. One of the key features of Azure Virtual Network is Subnet Delegation, which enables you to delegate control over specific subnets to Azure services. Subnet Delegation allows an Azure service to have its permissions and access controls, making it easier to manage and secure network infrastructure. In this article, we will explain Subnet Delegation, how it works in Azure Virtual Networks, and the benefits of managing complex network infrastructures in the cloud.

What is Subnet Delegation?

Subnet delegation is the process of delegating the management of IP addresses within a subnet to a specialized resource provider. In Azure, customers can delegate the management of IP addresses within a subnet to a specific Azure service, such as Azure Kubernetes Service (AKS), Azure Functions, or Azure App Service Environment (ASE). This enables customers to simplify network configuration and management, improve network security, and increase the flexibility and performance of their network resources.

Consider the below flow chart showing how Subnet Delegation works in Azure:

First, you create a subnet in Azure Virtual Network.

Next, you enable subnet Delegation for Azure Service you want to use with the Subnet. This step involves configuring the Azure Service to recognize and use the delegated subnet for specific purposes.

Finally, you assign the delegated subnet to the Azure Service. This allows the Azure Service to use the IP address within the subnet for a specific purpose.

Why Subnet Delegation is important?

Subnet delegation is important because it enables customers to delegate the management of IP addresses within a subnet to a specialized resource provider. This can help to simplify network configuration and management, improve network security, and increase the flexibility and performance of network resources. Here are some of the key benefits of subnet delegation in Azure Virtual Network:

1. Simplifies network management: It enables customers to delegate IP management to a specialized resource provider, simplifying network management and reducing administrative overhead.
2. Improves network security: It helps improve network security by isolating different resources within a subnet. It also reduces the risk of exposing sensitive resources to other resources.
3. Increases flexibility: It enables customers to delegate IP management to various Azure services such as AKS, Functions, or ASE. This increases flexibility and improves the overall experience.
4. Enhances performance: It provides better performance by optimizing the routing of network traffic. This helps to reduce latency and improve the overall performance of network resources.

How to Configure Subnet Delegation in Azure Virtual Network

To configure subnet delegation, below are some of the requirements that you need to meet:

1. Azure account with an active subscription.
2. If you didn’t create the subnet you would like to delegate to an Azure service, you need the following permission: Microsoft.Network/virtualNetworks/subnets/write.
3. Use Bash environment in Azure Cloud Shell.
4. Azure PowerShell installed locally or Azure Cloud Shell.
5. If you use AKS in a delegated subnet, you need to use AKS version 1.19.0 or later.
6. If using Azure Firewall, you need to use Azure Firewall Premium SKU.
7. The Delegated services must support subnet delegation. Not all Azure services support subnet delegation. So, you need to check the documentation for the specific service you want to use.

Here are the steps to configure subnet delegation using PowerShell:

STEP 1: Create a Virtual Network

First, you need to authenticate and connect to your Azure Subscription using the ‘connect-AzAccount‘ cmdlet. Then, create a new virtual network using the ‘New-AzVirtualNetwork‘ cmd.

Connect-AzAccount 

$resourceGroupName = "subnet-delegation-rg" 
$virtualNetworkName = "my-virtual-network" 
$addressPrefix = "10.0.0.0/16" 
$subnetName = "my-subnet" 
$subnetPrefix = "10.0.0.0/24" 

# Create a new virtual network 
New-AzVirtualNetwork ` 
  -ResourceGroupName $resourceGroupName ` 
  -Name $virtualNetworkName ` 
  -AddressPrefix $addressPrefix ` 
  -Location "eastus" 

# Create a new subnet in the virtual network 
New-AzVirtualNetworkSubnetConfig ` 
  -Name $subnetName ` 
  -AddressPrefix $subnetPrefix ` 
  | Add-AzVirtualNetworkSubnetConfig ` 
  -VirtualNetworkName $virtualNetworkName ` 
  -Name $subnetName ` 
  -AddressPrefix $subnetPrefix ` 
  | Set-AzVirtualNetwork

STEP 2: Delegate Subnet to an Azure Service

You can delegate the subnet to an Azure service using the ‘New-AzDelegation' cmdlet and update the subnet using the ‘Set-AzVirtualNetworkSubnetConfig' cmdlet.

# Delegate the subnet to Azure Kubernetes Service (AKS) 
$delegatedServiceName = "Microsoft.ContainerInstance/containerGroups" 
$delegationName = "aks-delegation" 

$delegation = New-AzDelegation ` 
  -Name $delegationName ` 
  -ServiceName $delegatedServiceName 

$subnet = Get-AzVirtualNetworkSubnetConfig ` 
  -VirtualNetworkName $virtualNetworkName ` 
  -Name 

$subnetName $subnet.Delegations = @($delegation) 
Set-AzVirtualNetworkSubnetConfig ` 
  -VirtualNetworkName $virtualNetworkName ` 
  -Name $subnetName ` 
  -Delegations $subnet.Delegations

STEP 3: Remove Subnet Delegation from an Azure Service

To remove subnet delegation from an Azure service, you can simply remove the delegation object from the subnet and update the subnet using the ‘Set-AzVirtualNetworkSubnetConfig' cmdlet.

# Remove delegation from the subnet 
$subnet = Get-AzVirtualNetworkSubnetConfig ` 
  -VirtualNetworkName $virtualNetworkName ` 
  -Name 

$subnetName $subnet.Delegations = @() 
Set-AzVirtualNetworkSubnetConfig ` 
  -VirtualNetworkName $virtualNetworkName ` 
  -Name $subnetName ` 
  -Delegations $subnet.Delegations

That’s It!

Note: Code may vary depending on the Azure SDK and programming language you are using.

Benefits of Subnet Delegation

1. Subnet Delegation enhances network security by reducing the risk of unauthorized access to the virtual network.
2. Delegation helps to improve network performance by optimizing traffic routing.
3. It also enables customers to implement more complex network architecture.
4. Subnet delegation reduces the burden of IP address management by allowing customers to delegate management tasks to specialized resource providers.

Limitations of Subnet Delegation

1. It can introduce network security risks if not configured particularly if unauthorized users gain access to the delegated resource.
2. Performance issues can arise if the delegated service provider does not optimize network traffic routing. Hence, leading to sub-optimal traffic flow and increasing the latency.
3. If multiple services use the same delegated subnet within the same virtual network, this will lead to more complex routing rules and increased management overhead.
4. Additionally, if a customer wants to change service providers, they have to reconfigure their network topology, which will be time-consuming and disruptive.
5. Subnet Delegation is not compatible with certain Azure Service providers.

Conclusion

Subnet delegation enables customers to delegate IP management to specialized resource providers such as Azure Kubernetes Services, Functions, and ASE. This simplifies network configuration and management, improves network security, and increases the flexibility and performance of network resources. However, customers should be aware of the limitations of subnet delegation and take steps to ensure that it is configured properly to minimize the risk of network security breaches and performance issues. Overall, subnet delegation is a valuable tool for customers who want to optimize their Azure Virtual Network infrastructure and simplify network management.