failed to setup up remote access XDMCP on RHEL 7.3

I have followed the steps outlined under https://access.redhat.com/solutions/2736 to enable remote access from Windows machine.

Apart from opening up 6000-6010/tcp on firewall, I have also open up 177/udp & 7100/tcp.

When I launch Xming on Windows, all I get is a blank screen. Is there other configuration I need to enable?

Environment info:
RHEL 7.3
uname -a
Linux Sandbox 3.10.0-514.el7.x86_64 #1 SMP Wed Oct 19 11:24:13 EDT 2016 x86_64 x86_64 x86_64 GNU/Linux

Windows 10 Pro
XMing Release 6.9.0.31