Approach: Convert ipxe.efi to ISO (simpler)

Download prebuilt ipxe.efi

Create ISO

xorriso -as mkisofs -o ipxe.iso -b ipxe.efi -no-emul-boot
-isohybrid-mbr /usr/lib/GRUB/efimbridge.bin
-c boot.cat
-V "iPXE"
-l
--allow-disc
-e ipxe.efi
-b ipxe.efi
/dev/null

Or with genisoimage + xorriso

mkdir iso_root cp ipxe.efi iso_root/ipxe.efi cat > iso_root/boot.ipxe << 'EOF' #!ipxe kernel http:///vmlinuz ip=dhcp root=/dev/ram0 ramdisk_size=... initrd http:///initrd.img boot EOF

xorriso -as mkisofs -o ipxe.iso -b iso_root/ipxe.efi -no-emul-boot
-isohybrid-mbr -c boot.cat -V "iPXE" -l iso_root

Key point: The boot.ipxe file can be included in the ISO or hosted alongside ipxe.efi — the EFI firmware can load it directly via the iPXE shell:

#!ipxe chain http:///boot.ipxe || shell