ISU does not have a KMS server that licenses Windows Server installs. The ISOs we provided for 2008 R2 will be good for 30 days without entering a key. Just to verify this, I accessed your two active Windows VMs (RDP and your DC rebuild); both report that they are set to 30-day expiration. In the event that those do start complaining sooner, you can always re-arm as well using: slmgr.vbs /rearm