XVnc does not present GDM Greeter (Login) after openvpn installed - XDMCP

I thought I'd write this up so that it can help anyone else who hits the same issue.

I have a Xvnc set up on my Debian Wheezy (7) with xinetd serving on ports 5900 and up.

All was working fine until I installed openvpn and set up a tunnel to my other site.

After that, I could connect using vnc but Xvnc would only show the default X background - Xvnc was not connecting to GDM using XDMCP to present the login and complete the Display Manager startup.

After a bit of strace'ing of the gdm3 process - the server for XDMCP UDP port 177 - it became obvious that gdm was having trouble resolving the IP Addresses. It all started working when I added the tunnel's local address in the /etc/hosts.

Here's the important parts of the etc/gdm3/daemon.conf:

[security]

DisallowTCP=false

[xdmcp]

Enable=true

DisplaysPerHost=3

Here's the /etc/xinetd

service Xvnc

{

        type = UNLISTED

        disable = no

        socket_type = stream

        protocol = tcp

        wait = no

        user = nobody

        server = /usr/bin/Xvnc

        server_args = -inetd -desktop Acer -query localhost -depth 24 -cc 3 -once -SecurityTypes=none -x XFIXES -geometry 1280x1024 -geometry 1440x900 -geometry 1024x768 -geometry 2560x1440

        port = 5901

}

And as my host has the following Interfaces:

eth0: 192.168.15.10

lo: 127.0.0.1

tun0: 192.168.88.6

Here is my /etc/hosts:

127.0.0.1       localhost

127.0.1.1       acer.cregganna.com      acer

192.168.15.10   acer.cregganna.com      acer

192.168.88.6    acer.cregganna.com      acer