RE: Info on "Can't open display"

["Christopher Landrieu" <landrieu at hotmail dot com>]

Harold,

I appreciate your reply.

I originally considered that it could be an interaction with VPN software 
because I do have VPN packages on both computers, however the problems occur 
whether the VPN software is active or not.

As well, the problem is not with all programs making TCP/IP connections to 
port 6000 on the localhost.  That is evidenced by the fact that the TeraTerm 
SSH with X Forwarding worked.  X Forwarding works by having the remote SSH 
server set up a dummy X server on the remote machine (display 10 - :10.0) 
and setting the DISPLAY variable to remote-machine:10.0.  The SSH server 
then tunnels the X traffic through the encrypted SSH socket to the SSH 
client.  The SSH client opens a connection to the local X server 
(localhost:0.0).  The SSH client redirects the tunneled X traffic from the 
SSH Socket to the connection to the local X server.

Therefore, TeraTermSSH is successfully making a working X connection to 
localhost:0.0.  TeraTermSSh in this case is technically an X client.  The 
only programs that fail to successfully connect are the local X clients from 
XFree86.

Also, the local X clients cannot even connect properly to a remote X server. 
  I believe that the TCP/IP connection is being established successfully but 
that these local X clients are not successfully setting up the X11 protocol 
connection.  This is because when I try to run "xterm -display 
remote-x-server:0.0", I can see the connection openned on the remote machine 
("netstat -np" as root on my linux box).  I believe the X server is then 
dropping the connection (like when I do the "telnet localhost 6000" test).

That is why I would like to try and sniff the packets and see what 
communication is taking place between the X server and the X clients.

I'll let you know what I find.

Chris

>From: "Harold Hunt" <huntharo@msu.edu>
>To: <landrieu@hotmail.com>
>Subject: RE: Info on "Can't open display"
>Date: Wed, 6 Jun 2001 13:24:10 -0400
>
>Chris,
>
>Hopefully you can identify the exact conditions that cause this, as we
>haven't yet had a thorough examination of this problem.
>
>You might want to take a look at the current information we have regarding
>this problem, as answered in my draft FAQ:
>http://www.msu.edu/~huntharo/xwin/docs/faq/cygwin-xfree-faq.html#AEN290
>
>A couple users have reported that removing VPN or firewall software solved
>their problems.  It makes sense that VPN software would cause a problem, as
>VPN software usually causes connections to be redirected to a VPN tunnel;
>when a request for 127.0.0.1:6000 or host-name-or-ip-address:6000 shows up
>at the end of the VPN tunnel, the computer at the end of the VPN tunnel
>can't satisfy the request, so the connection fails.  (The VPN machine isn't
>running Cygwin/XFree86, so 127.0.0.1:6000 would fail; as for
>host-name-or-ip-address:6000, the VPN software may reject that because it 
>is
>looping the VPN back onto itself.)
>
>It would have to be pretty braindead VPN software that causes this problem,
>as 127.0.0.1 should never be redirected.  I used the included VPN support
>with Windows 2000, but I never had problems.  Users of lesser known VPN
>software seem to be the ones reporting problems :)
>
>Uninstalling VPN or firewalling software from a machine doesn't always fix
>the problem, as the uninstall program may leave certain files and settings
>in place, thus preserving the problem.
>
>Anyway, let me know what you come up with,
>
>Harold
>

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