Run the following steps from a Terminal...

  1. open /etc/sysctl.conf using a text editor with the following command...
    run: gksudo gedit /etc/sysctl.conf
  2. Insert the following lines at the end:
    net.ipv6.conf.all.disable_ipv6 = 1
    net.ipv6.conf.default.disable_ipv6 = 1
    net.ipv6.conf.lo.disable_ipv6 = 1
  3. run: sudo sysctl -p
  4. run: cat /proc/sys/net/ipv6/conf/all/disable_ipv6
  5. If you see an output of '1' then IPv6 has been successfully disabled.