iface ens3 inet6 manual
  up   ip route add 2001:db8:0:15::/64 dev ens3
  up   sysctl -w net.ipv6.conf.ens3.forwarding=1
  up   sysctl -w net.ipv6.conf.all.forwarding=1 #TODO: why?
  down ip route del 2001:db8:0:15::/64 dev ens3
  ip-forward on