booting ipxe from pxelinux

[jwm77]

using pxelinux.0 (Version 4.04) I could boot ipxe in this way:

LABEL IPXE_shell
KERNEL /ipxe/IPXE.KRN ipxe command (eg. Shell)

using pxelinux (Version 6.01) this works no more
getting: "invalid argument" error.

same error occurs if I try

LABEL IPXE_shell
KERNEL /ipxe/IPXE.KRN
INITRD myscript.ipxe

Is there a workaround?
How to transfer a commandline to ipxe?
I perfer solutions without creating different configurations of ipxe because administration of versions is cumbersome.
pxelinux (v 5.x) I have never used

[robinsmidsrod]

What happens if you put your "ipxe command, e.g. shell" on an APPEND line inside your pxelinux config file? Does that work?

If you just start ipxe.krn without any command, does it allow you to press Ctrl-B to get to the iPXE shell? If so, your issue is specifically getting the scriptlet variable set properly. If you had it working with syslinux 4.xx then I suggest you carefully examine the changelogs between version 4 and 6 and see if they mention anything about incompatibilities with iPXE or loading bzImage kernel images.