hi,
this question has popped up a couple of times so - Andreas made a doc on how to configure DHCP for WDS etc, which you can use as a reference. DL it here:
http://2pintsoftware.com/download/using-dhcp-to-control-wds-pxe-boots-for-bios-efi-clients/
For the iPXE boot loaders you would configure option 67 as follows
boot\x64\snponly.efi for EFI
boot\x86\undionly.kpxe for BIOS