If you want IPv6 disabled permanently on an Ubuntu 16.04 system, here’s a good way to do it. Disabling it like this should keep it disabled permanently, even after performing updates that could potentially enable it again without you knowing it. I haven’t tested it, so I’m not 100% certain, but if you decide to upgrade Ubuntu to 16.10 or the most recent version, it should still have ipv6 disabled …
