use dnsmasq as proxy
use dnsmasq tftp server
change the path and ip to your system path and ip
that works on ASUSTOR 
dnsmasq.conf
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port=0
#log-dhcp
enable-tftp
tftp-root=/volume1/pxe
dhcp-range=xxx.xxx.xxx.xxx,proxy  ( xxx.xxx.xxx.xxx your ip dhcp server adress)
pxe-prompt="Taste F8 zeigt Auswahl",20
pxe-service=X86PC,"Starten von Festplatte",0
pxe-service=X86PC,"Mit Menue starten",pxelinux
bridge-interface=bond0, eth0, eth1
dhcp-leasefile=/volume1/pxe/dnsmasq.leases
# a TFTP server; either dnsmasq's built in TFTP server or an
# external one. (See below for how to enable the TFTP server.)
dhcp-boot=pxelinux.0
tftp-port-range=1028,1030
# Boot for Etherboot gPXE. The idea is to send two different
# filenames, the first loads gPXE, and the second tells gPXE what to
# load. The dhcp-match sets the gpxe tag for requests from gPXE.
#dhcp-match=gpxe,175 # gPXE sends a 175 option.
#dhcp-boot=net:#gpxe,undionly.kpxe
#dhcp-boot=mybootimage 
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dnsmasq start  (   S98dnsmasq.sh  )
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#!/bin/sh
if [ -f /var/run/dnsmasq.pid ] ; then
  kill `cat /var/run/dnsmasq.pid`
fi
rm -f /var/run/dnsmasq.pid
sleep 2
/volume0/usr/builtin/sbin/dnsmasq -C /volume1/Optware/dnsmasq.conf
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