Azure: Error while using Azure virtual network, It says subnet is not valid in virtual network - azure-virtual-network

Question

$rg1="firstyear-rg-01"
$loc="eastasia"
New-AzResourceGroup -name $rg1 -location $loc
$ec1 = New-AzVirtualNetworkSubnetConfig -Name "ec-lab-sn-01" -AddressPrefix "10.0.0.0/27"
$cs1 = New-AzVirtualNetworkSubnetConfig -Name "cs-lab-sn-01" -AddressPrefix "10.0.1.0/27"
$it1 = New-AzVirtualNetworkSubnetConfig -Name "it-lab-sn-01" -AddressPrefix "10.0.2.0/27"
$mc1 = New-AzVirtualNetworkSubnetConfig -Name "mech-lab-sn-01" -AddressPrefix "10.0.3.0/27"
$vn1 = New-AzVirtualNetwork -Name "firstyear-vn-01" -ResourceGroupName $rg1 -Location $loc -AddressPrefix "10.0.0.0/25" -Subnet $ec1,$cs1,$it1,$mc1
The above is the exact code I tried, but it gives error:
New-AzVirtualNetwork: Subnet 'cs-lab-sn-01' is not valid in virtual
network 'firstyear-vn-01'. StatusCode: 400 ReasonPhrase: Bad Request
ErrorCode: NetcfgInvalidSubnet ErrorMessage: Subnet 'cs-lab-sn-01' is
not valid in virtual network 'firstyear-vn-01'. OperationID :
c5bd59de-a637-45ec-99a7-358372184e98
What am I doing wrong?

Answer 1

If you are using a virtual network with an address range 10.0.0.0/25, the subnet AddressPrefix should be included in that virtual network. You can assign subnets to address prefixed like 10.0.0.0/27, 10.0.0.32/27, 10.0.0.64/27, 10.0.0.96/27 according to the IP Calculator.

Answer 2

I ran into this issue when setting up a subnet in Azure using Terraform.
When I run terraform apply, I get the error below:
module.subnet_private_1.azurerm_subnet.subnet: Creating...
╷
│ Error: creating Subnet: (Name "my-private-1-dev-subnet" / Virtual Network Name "my-dev-vnet" / Resource Group "MyDevRG"): network.SubnetsClient#CreateOrUpdate: Failure sending request: StatusCode=0 -- Original Error: Code="NetcfgInvalidSubnet" Message="Subnet 'my-private-1-dev-subnet' is not valid in virtual network 'my-dev-vnet'." Details=[]
│
│ with module.subnet_private_1.azurerm_subnet.subnet,
│ on ../../../modules/azure/subnet/main.tf line 1, in resource "azurerm_subnet" "subnet":
│ 1: resource "azurerm_subnet" "subnet" {
Here's how I fixed it:
The issue was that I was assignining subnet_address_prefixes that were already assinged to a subnet to the new subnet.
I had already assinged ["10.1.1.0/24"] to an already existing subnet, and I made a mistake in my module to assign it again to the new subnet that I was creating.
All I had to do was to use a different subnet_address_prefixes, which is ["10.1.2.0/24"] and everything worked fine.

Answer 3

In your case, this is because your chosen IP Ranges of the subnets are not part of the Virtual Network IP Range.
Generally such error can occur either because of a subnet with the same name already exist, your chosen ip subnet range is not part of the virtual network ip range or your chosen subnet ip ranges are overlapping.
When you are not sure about the boundaries of your IP Ranges, you can use an IP Range calculator.
As you can see here, your virtual network ranges from 10.0.0.2 to 10.0.0.126. Therefor none of your subnets is in that range as you used:
"10.0.0.0/27","10.0.1.0/27","10.0.2.0/27","10.0.3.0/27"
Depending on the size you need, you can go for a configuration as suggested by #nancy Xiong.
Virtual network : 10.0.0.0/25
subnets: 10.0.0.0/27, 10.0.0.32/27, 10.0.0.64/27, 10.0.0.96/27