boot from a large iso file

[robinsmidsrod]

Normally, you can't access the contents of an ISO after the kernel has booted. You'll need to tell the kernel how to access the files it needs from a network resource.

Here it seems like the ISO is generated in a way that is incompatible with memdisk. Since you're dealing with CentOS, I would recommend that you unpack the ISO and boot CentOS directly using the kernel and initrd found on the ISO.

There should be some tutorials on how to boot CentOS using PXE. The tutorials might be based on PXELINUX, but it should be quite simple to rewrite it to ipxe.