[breppp]

Roughly from memory iPXE is a bootable image that acts similar to a PXE BIOS, so you boot to that image like a regular disk. It acts like a bios by for example hooking your interrupts for storage reads.

In order to find where the image is, you need some kind of discovery mechanism. This is where DHCP comes in. Remember this is all happening before you have an OS, so it has to be very bare bones