Configuring Foreman DHCP server for PXE boot to only respond to certain statically configure MAC address

This post bellow states:

“There’s a external iPXE server (10.10.1.217) already configured that successfully installs the Discovery Image to network booted clients.”

Seems like he is somehow doing a network boot and loading the Discovery with and iPXE without DHCP? I’ll searched online not sure how that is possible. but if it is, that would possibly solve my problem.

Thanks