You need to enter the MAC ID to your "grub.cfg" of your booting IMG or ISO.
set vid=0x058f
set pid=0x6387
set sn=A8ODN02468
set mac1=ADD YOUR MAC ADR HERE without :
set rootdev=/dev/md0
set netif_num=1
#set extra_args_3617='earlycon=uart8250,io,0x3f8,115200n8 earlyprintk loglevel=15'
set extra_args_3617=''
well thats all. After that you can boot your loader and join your ip over the internet to install DSM.
Demens's post in Install over Internet - External IP (08.2018) was marked as the answer