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
