Hmm, I had this working in an environment a while back, but not currently. I'm looking at an old config and it seems I had these settings. I hope it helps somewhat
set service dhcp-server global-parameters 'allow booting;' set service dhcp-server global-parameters 'allow bootp;' set service dhcp-server global-parameters 'option option-128 code 128 = string;' set service dhcp-server global-parameters 'option option-129 code 129 = text;' set service dhcp-server global-parameters 'filename "/pxelinux.0";' set service dhcp-server global-parameters 'next-server 10.10.10.10;'
Maybe you need to allow booting and bootp? And definte the specific numbered options?