Cheat sheet on Azure Subnetting

Here’s a quick cheat sheet on recommended subnet sizing for Azure. Items in bold are subnet names reserved by the platform for their corresponding service.

GatewaySubnet – /27 – https://docs.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-about-vpn-gateway-settings#gwsub

Point-to-Site (P2S) addressing (VPN or VWAN) – Requires a non-vnet address space – depends on how many P2S clients – https://docs.microsoft.com/en-us/azure/vpn-gateway/point-to-site-about#gwsku

AzureBastionSubnet – /27 – https://docs.microsoft.com/en-us/azure/bastion/bastion-create-host-portal#createhost

Azure Virtual WAN Hub – /24 – https://docs.microsoft.com/en-us/azure/virtual-wan/virtual-wan-site-to-site-portal#hub

AzureFirewallSubnet – /25 – https://docs.microsoft.com/en-us/azure/firewall/tutorial-firewall-deploy-portal#create-a-vnet

Application Gateway – min /27 – https://docs.microsoft.com/en-us/azure/application-gateway/configuration-overview#size-of-the-subnet

Azure SQL Managed Instance (SQL MI) – min /27 – https://docs.microsoft.com/en-us/azure/sql-database/sql-database-managed-instance-determine-size-vnet-subnet

App Services (Web Apps, Functions, API Apps) – min /27 – https://docs.microsoft.com/en-us/azure/app-service/web-sites-integrate-with-vnet

App Service Environment – /24 – https://docs.microsoft.com/en-us/azure/app-service/environment/network-info

Logic Apps integration service – /27 – https://docs.microsoft.com/en-us/azure/logic-apps/connect-virtual-network-vnet-isolated-environment#set-up-network-ports

API Management – min /29 – https://docs.microsoft.com/en-us/azure/api-management/api-management-using-with-vnet#–subnet-size-requirement

Azure Kubernetes Service (AKS) – depends on node count –  https://docs.microsoft.com/en-us/azure/aks/configure-azure-cni#plan-ip-addressing-for-your-cluster

Azure Container Instances (ACI) – /29 – https://docs.microsoft.com/en-us/azure/container-instances/container-instances-vnet

Azure Databricks – Requires 2 subnets (Public/Private) – min of two /26 – https://docs.azuredatabricks.net/administration-guide/cloud-configurations/azure/vnet-inject.html#virtual-network-requirements

Azure NetApp Files – /28 – https://docs.microsoft.com/en-us/azure/azure-netapp-files/azure-netapp-files-delegate-subnet

Azure Dedicated HSM – /28 – https://docs.microsoft.com/en-us/azure/dedicated-hsm/networking#subnets

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