iPXE fails to boot anything

[robinsmidsrod]

memtest is a single binary application that is working in BIOS mode, that's why it's working without issues.

ISO files can't boot unless they are specifically made to work purely from a ramdisk that is loaded ONCE and then do not access the medium they are loaded from to fetch additional files. Any ISO that uses that approach will not work unless the initrd/ramdisk has special support in it to load the additional files off the network. Most ISOs that can also be loaded to a USB device have drivers for optical drives and other local storage (like USB) so that it can find additional files on those kind of devices automatically. Unfortunately it's not possible to load information from the network in a purely automatic way for most ISOs without additional configuration. E.g. Debian and Ubuntu LiveCDs can be booted from NFS or SMB because the ramdisk (casper) has support for that.

I'm surprised to hear that atih11.iso works using regular PXE/TFTP, but not using ipxe. How do you boot atih11.iso using regular PXE? Do you actually mean, using pxelinux and memdisk?

I think you should enable either serial or syslog logging so that you can post a log of what you experience with exact screenshots and error messages shown. Then we might be able to help you out more.