@ikt_le Hi, not sure what system you are using for DHCP but if it is windows please have a look at the guide below
https://wiki.fogproject.org/wiki/index.php/BIOS_and_UEFI_Co-Existence follow this, but please add the fog server IP to option 66. Also if you have subnets you need to complete this on each subnet scope on the dhcp server. Also if you have 2 DHCP servers you must do it on each one and on each subnet (unless is copies over properly between the servers, mine didn’t last time i set it up)