@george1421 ok so lets wrap this thread up nice and neat.
On the HP EliteDesk 705 G5 computers, they for what ever reason, do not like the unidonly.kpxe iPXE boot loader. iPXE undionly.kpxe will issue a dhcp request and the dhcp servers will send an OFFER packet but iPXE rejects the offer and just sends a DISCOVER packet again. And it continues over and over with the DISCOVER and receiving an OFFER but rejecting the given OFFER.
We did find that ipxe.kpxe did work correctly on these HP systems. So this kind of tells me the UNDI firmware driver in the network adapter is faulty. I’m suspecting a future firmware update will address the issue. In the mean time we had to work out a solution to send ipxe.kpxe to these computers only and send undionly.kpxe to all other bios based systems. Luckily the OP had linux dhcp servers on this subnet so we set out to see if we can identify these systems based on their UUID. Through testing unfortunately the UUID on these HP systems are globally unique instead of encoding the model and unique ID in the UUID field like Dell does. So the OP settled on identifying the systems based on mac prefix. This is the following setting we added to the isc-dhcp server on his network.
class “Legacy-hpbroken” { match if (substring(option vendor-class-identifier, 0, 20) = “PXEClient:Arch:00000”) and (substring(hardware, 1, 3) = 00:01:02;); filename “ipxe.kkpxe”; }