[teraflop]

There are a bunch of different options to "bootstrap" iPXE in the first place. Least invasive is probably to boot it from a USB drive. You can also set up a traditional PXE boot process using DHCP/TFTP on your network to "chain-load" iPXE (if your client's network card supports PXE), or you can even flash iPXE into the boot ROM on certain network cards.

However you do it, once iPXE starts running, it will take control of the NIC and fetch the actual OS images that it needs from the internet over HTTP.

[Joe_Cool]

Some HP server UEFIs also support boot from http. So you can boot the .efi executable directly from the internet. For https you need to enroll the certificate first and it's a bit more involved.

I am sure there are other implementations I have only seen it on HP servers so far.