we want to boot the PI 4 from the network without an sd card. We already have an old system that works on the old pis with a minimal image that gets from the DHCP server the boot server.
Is something like that also possible with the PI 4 without TFTP or does the pi 4 netboot only work with TFTP?
As far as I know specification of netboot is to use the tftp (Trivial File Transfer Protocol) to get the boot image from any server. Usually you install a tftp server for it, but it may be possible that a server application encapsulated this protocol. If that were the case, you wouldn't have to install a tftp server. An example of such a program is dnsmasq.
As of today however, you cannot netboot a Raspberry Pi 4B because it isn't supported. This is noted at Raspberry Pi boot modes:
The Raspberry Pi 4B does not use the bootcode.bin file - instead the bootloader is located in an on-board EEPROM chip. The Pi 4B bootloader currently only supports booting from an SD card. Support for USB host mode boot and Ethernet boot will be added by a future software update. See Pi4 Bootflow and SPI Boot EEPROM.
Therefore, it seems you will have to wait a while for netbooting with a Raspberry Pi 4B.
You definitely can netboot a 4B, I'm doing it.
See: https://linuxhit.com/raspberry-pi-pxe-boot-netbooting-a-pi-4-without-an-sd-card/
TFTP is required for netboot, that's just the way it's defined.
