Hi,
After hours of tries, we failed to install .net 3.5 on a server running Windows 2012 R2 Std Ed from the ROK DVD media.
As workaround, we finally installed Windows 2012 R2 from a "normal" media (Microsoft select ?), enabled .net 3.5 feature and activated the OEM license in two steps.
1) Register the oem licence via : slmrg.vbs /ipk xxxxx-xxxxx-xxxxx....
2) Activate licence from the control panel (system)
Max