Windows Deployment Services allows you to deploy WMI Images via PXE Boot. The PXE Boot setting is configured in DHCP Option 67.
However, UEFI BIOS and Legacy BIOS need different values for this DHCP Option. Most computers these days are UEFI, but occasionally you may need to change it back to re-image an older Legacy BIOS.
DHCP Option 67: UEFI Boot
DHCP Option 67: Legacy Boot
There you have it. These values apply to a standard Windows Deployment Services installation on Windows Server 2008 R2.