XDMCP and NAT

[Ritesh Sood]

Hi all,

This mail is more of a feature request, and looking at the number of
messages on the web, I'm sure quite a number of users would be happy to
have this functionality, which is already provided by many commercial
Xservers for windows.

I want use Xephyr/Xnest on my home machine local_host (as display :1)
and have the display controlled by xdm running on a remote application server
(app_server)

First, please have your browser's font set to a monospaced one so that
the boxes below are displayed correctly.

Here's how the network "topology" looks like.

+---------------+         +------------+          +-------------+
| local_host    |         | NAT server |          | app_server  |
| 192.168.0.100 |-------> | 1.2.3.4    |--------->| 5.6.7.8     |
| running Xnest |         |            |          | my.univ.edu |
                  |   my.univ.edu  |
| on display :1 |         | my.isp.com |          | running xdm |
+---------------+         +------------+          +-------------+

At the app_server end, Xaccess contains
*.univ.edu   NOBROADCAST
*.isp.com   NOBROADCAST
to have some measure of security

I'm running xdm as
# xdm -debug 1 -config ....

Within the university network of-course, things work very well. From
local_host too, at-least XDMCP authentication is happening correctly,
i.e. xdm sees that the incoming request is from *.isp.com. and considers
it legitimate.

Next, it tries to open 192.168.0.100:1 for login window, etc; and that
of-course fails.

Just to make sure that port forwarding on 60xx ports is happening correctly,
I do
$ xterm -display my.isp.com:1.0
and that works alright.

As i mentioned above, many Xserver implementations for windows provide
an option so that the NAT IP address can be passed to xdm instead of
XDMCP picking up the local_host address by default. See these FAQs, for
instance:
http://connectivity.hummingbird.com/support/nc/exceed/exc9003009.html?cks=y
http://www.netsarang.com/products/xmg_faq.html

It would be great if we could have similar functionality in the Xorg
Xservers.

Thanks everyone for taking the time to read my mail and for your wonderful
work.

Regards,
Ritesh.