Ununtu Disabled ipv6

root@server:~# netstat -atnup | grep 177
udp6       0      0 :::177                  :::*                                4146/gdm-binary

I disabled IPv6 via the Kernel Boot Parameters:

I added "ipv6.disable=1" to the Config Line GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" in /etc/defaults/grub.

$ grep -i ipv6 /etc/default/grub 
GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet splash"

Then updated grub via the command "sudo update-grub" and rebooted.

Now gdm listens on the UDP in IPv4.

$ sudo netstat -tuanp |grep gdm
udp        0      0 0.0.0.0:177             0.0.0.0:*    607/gdm-binary