Create App Service Environment Subnet address space issue

Question

I am trying to create a new Azure App Service Environment within an existing virtual network that contains two address spaces. In this case I am trying to create the subnet in the second address space as shown below.

When I then try to create a new Subnet Address Block of 172.31.12.0/25 the Azure Portal tells me that the "Subnet not contained in the address space". Surely this is correct as the CIDR Range is from 172.31.12.0 - 172.31.12.127 for this range.

The sites validation will allow me to create a small range within the 172.31.11.0/24 range but this isn't what I need.

Anyone know what I am missing here?

Answer 1

It's the same error as you on my side. It looks like a restriction or something else like that on the Azure portal. It seems that you only could select the subnet address block from the original address space for the ASE. Even I change to select the Virtual Network Address Block to the second address space and create the subnet in the original address space, this still works.

update

As a workaround, you could create an ASE subnet from the second address space via this ARM template.

1. Create a second address space in the Azure VNet mynettest
2. Create a subnet2 in this address space.
3. Use the above parameters to deploy the template. Create an ASE in the subnet2.