Nested Hyper-V

Would someone be able to confirm is this is only available on server 2016 and Windows 10, but not the older Server 2012r2? Thank you!

i belive it's a mater of supported or not. but if doing in a lab... why not?

Yeah, it's a function of the latest changes so Windows 10 Anniversary or Server 2016. No, you can't nest in 2012 r2, simply won't work at all. It's not just a matter of support, it simply won't run.

Server 2016 added a specific VM configuration to enable nested virtualization. It must be enabled via PowerShell:
Set-VMProcessor -VMName (name) -ExposeVirtualizationExtensions $true

Once that is set and you boot up the VM, you can then install the Hyper-V role on the guest. I've been using this on my own home lab and is much more stable than VMWare's nesting.

This feature is not available in 2012R2 and older, but is available on Windows 10 since it is the same underlying components as 2016