On a recent project, a client had a requirement for all Public IP addresses to be part of a Pubic IP Address Prefix. This ensured they could both re-use and predict their IPs. Greatly simplifying Governance requirements and white-listing with partners.
However, once the Prefix was active, I went to create a Virtual Network Gateway to test some connectivity options. Being a simple test, I was using the Portal for deployment. I realised that the parameter defaults prevent you from using a Prefix IP as they are on the Standard SKU by default. If you’re creating a single VNG that is not linked to an Availability Zone, the Portal looks for a Basic SKU and you receive this error:
Now a quick fix was to simply select one the AZ SKUs, but I didn’t want that. Thankfully, Cloud Shell was my answer. Out of curiosity, I then tried the same process, but via Powershell. Using the exact same resources and parameters.
And…success! My guess is the flag that prevents you from using a Standard SKU Public IP address for a VpnGw1 SKU VNG is a parameter limitation rather than a technical one. The VNG works exactly as expected.
Hopefully this can save you some time if you find yourself in the same situation!
Bonus tip! When working in Cloud Shell, if there is a parameter you are unfamiliar with and not sure what it expects as input, type out the parameter and hit tab, it will list all allowed inputs: