SSH X11 Forwarding over PPTP VPN breaks connection

[Matt Austin]

Network:
I have an Ubuntu desktop machine at home and also an Ubuntu 7.10 desktop machine at work.

I can connect to work from home using PPTP VPN (to a Windows 2003 Server). The VPN connection works fine - I can browse samba shares and use sftp. I can SSH in to my desktop machine and use the command line without any issues.

However, as soon as I attempt to launch a program which uses X11 forwarding the entire VPN connection immediately stops working, I can no longer ping any machines at work.

I can connect to the machine with the X11 forwarding option without issue (ssh user@WorkMachine -X), the problem occurs when I run a program (e.g. gedit).

Tested (as the client) using Ubuntu 7.10 and Hardy beta - same problem happens on both.
However, X11 forwarding from my Ubuntu desktop at work is fine if I connect to work from home using Windows XP with Putty & Xming.

Not sure if the problem is in SSH, or VPN.

[Nicolas Valcarcel (nvalcarcel)]

Thanks for taking the time to report bugs on ubuntu.
Does the connection ends with an error message or simply stops working?
Also i don't understand the whole picture, you are connection from home to a Win 2k3 server and from this server to your desktop and trying to Forward X11 from this windows machine or you are connecting from home to work desktop forwarding X11?

[Matt Austin (mattaustin)]

Hi Nicolas,

Thanks for helping me with this bug.

When I launch a graphical program (e.g. gedit), the connection simply stops working. The SSH console hangs, as does the entire VPN connection (and eventually times out and gets disconnected). I can no longer ping any machines at work in my other terminal tab.

From home I connect to work. The Win2k3 server at work establishes my VPN connection - I can then access the LAN at work, which I then use to connect to my desktop machine at work.

I am attempting to forward X11 from my work desktop to my home machine (i.e. by connecting to my work desktop using "ssh user@workdesktop -X"). This connects without hitch, but as soon as I run a graphical app (e.g. "evolution") the VPN connection hangs.

The exception to this is if I boot my home machine into WinXP, and VPN to work - using Putty and Xming to establish the SSH connection to my work desktop then X11 forwarding works!

Apologies for the lack of clarity - it's a difficult situation to describe.

[Nicolas Valcarcel (nvalcarcel)]

This is a bug in vpn, not in openssh.

[Daniel T Chen (crimsun)]

Which vpn package are you using? Is this symptom reproducible in 8.10 or 9.04?

[Matt Austin (mattaustin)]

This is now working as expected using Ubuntu 8.10 / Ubuntu 9.04 Beta from home and using X forwarding from my work desktop (Ubuntu 8.10) over a PPTP VPN.

network-manager-pptp versions:
Ubuntu 8.10: 0.7~~svn20081015t024626-0ubuntu1.8.10.1
Ubuntu 9.04 Beta: 0.7.1~rc4.20090316+bzr23-0ubuntu2

[xteejx (xteejx-deactivatedaccount)]

This bug report is being closed due to your last comment regarding this being fixed with an update. For future reference you can manage the status of your own bugs by clicking on the current status in the yellow line and then choosing a new status in the revealed drop down box. You can learn more about bug statuses at https://wiki.ubuntu.com/Bugs/Status. Thank you again for taking the time to report this bug and helping to make Ubuntu better. Please submit any future bugs you may find.