Question about command line arguments

Hi all,
A while back it was recommended (to force encryption on all communication between client and server) to either put the server on a separate subnet OR add in the server args.txt or the client args.txt:
–internet_only_mode true

Ok - so I have installed the linux server for ubuntu using the ppa - I tried adding into the daemon_args of the start script but it came back not recognizing the command - so where do I put this to force the server into internet_only_mode?