Skip to content

Virtual Network Subnet must use standard naming#

Operational Excellence · Virtual Network · Rule · 2025_06 · Awareness

Virtual Network subnets without a standard naming convention may be difficult to identify and manage.

Description#

An effective naming convention allows operators to quickly identify resources, related systems, and their purpose. Identifying resources easily is important to improve operational efficiency, reduce the time to respond to incidents, and minimize the risk of human error.

Some of the benefits of using standardized tagging and naming conventions are:

  • They provide consistency and clarity for resource identification and discovery across the Azure Portal, CLIs, and APIs.
  • They enable filtering and grouping of resources for billing, monitoring, security, and compliance purposes.
  • They support resource lifecycle management, such as provisioning, decommissioning, backup, and recovery.

For example, if you come upon a security incident, it's critical to quickly identify affected systems, the functions that those systems support, and the potential business impact.

For subnets, the Cloud Adoption Framework (CAF) recommends using the snet- prefix.

Requirements for subnet names:

  • At least 1 characters, but no more than 80.
  • Can include alphanumeric, underscore, hyphen, period characters.
  • Can only start with a letter or number, and end with a letter, number or underscore.
  • VNET names must be unique within the parent VNET.

Recommendation#

Consider creating subnets with a standard name. Additionally consider using Azure Policy to only permit creation using a standard naming convention.

Examples#

Configure with Bicep#

To deploy virtual network subnets that pass this rule:

  • Set the name property to a string that matches the naming requirements.
  • Optionally, consider constraining name parameters with minLength and maxLength attributes.

For example:

Azure Bicep snippet
@minLength(1)
@maxLength(80)
@description('The name of the resource.')
param name string

resource subnet 'Microsoft.Network/virtualNetworks/subnets@2024-05-01' = {
  parent: vnet
  name: name
  properties: {
    addressPrefix: '10.0.0.0/24'
    networkSecurityGroup: {
      id: nsg.id
    }
    defaultOutboundAccess: false
  }
}

Configure with Azure Verified Modules

A pre-validated module supported by Microsoft is available from the Azure Bicep public registry. To reference the module, please use the following syntax:

br/public:avm/res/network/virtual-network/subnet:<version>

To use the latest version:

br/public:avm/res/network/virtual-network/subnet:0.1.1

Configure with Azure template#

To deploy virtual network subnets that pass this rule:

  • Set the name property to a string that matches the naming requirements.
  • Optionally, consider constraining name parameters with minLength and maxLength attributes.

For example:

Azure Template snippet
{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "metadata": {
    "_generator": {
      "name": "bicep",
      "version": "0.34.44.8038",
      "templateHash": "1920943566989111543"
    }
  },
  "parameters": {
    "name": {
      "type": "string",
      "minLength": 1,
      "maxLength": 80,
      "metadata": {
        "description": "The name of the resource."
      }
    }
  },
  "resources": [
    {
      "type": "Microsoft.Network/virtualNetworks/subnets",
      "apiVersion": "2024-05-01",
      "name": "[format('{0}/{1}', parameters('name'), parameters('name'))]",
      "properties": {
        "addressPrefix": "10.0.0.0/24",
        "networkSecurityGroup": {
          "id": "[resourceId('Microsoft.Network/networkSecurityGroups', parameters('name'))]"
        },
        "defaultOutboundAccess": false
      },
      "dependsOn": [
        "[resourceId('Microsoft.Network/networkSecurityGroups', parameters('name'))]",
        "[resourceId('Microsoft.Network/virtualNetworks', parameters('name'))]"
      ]
    }
  ]
}

Notes#

This rule does not check if subnets names are unique.

Rule configuration#

AZURE_VNET_SUBNET_NAME_FORMAT

To configure this rule set the AZURE_VNET_SUBNET_NAME_FORMAT configuration value to a regular expression that matches the required format.

For example:

configuration:
  AZURE_VNET_SUBNET_NAME_FORMAT: '^snet-'

Comments