X11 forward in SSH

[YLTan]

What the different bet. setting X11Forwarding and not setting it at the SSH server? I noticed in both cases I can still use Xwindows by putting up the appropiate DISPLAY parameters and able to spawn the Xwindows on my PC's. Is there a diff. in terms of encrypted X11 traffic in both cases?

[Jerome Baron]

Hi,

Effectively with X11 forwarding you can lunch graphical application with a ssh session. The only problem is your lan connection speed!
Without X11 forwarding I mean that you can't use graphical interface by ssh.

Configuration on server in /etc/ssh/sshd_config:
X11Forwarding yes
X11DisplayOffset 10
# Change the port for more security
Port 5522

restart ssd daemon

Configuration on client in /etc/ssh/ssh_config or??/.ssh/config :
ForwardX11 yes
Compression yes
Port 5522 # the same port that on server

Without client configuration :
# ssh -XC -p 5522 -l

Regards,
Jerome

[Jerome Baron]

oups I give you linux config file....

On HP-UX config file are in /opt/ssh/etc.

Regards,
Jerome

[YLTan]

Hi Jerome,

I test on both cases for X11Forward is yes and No, in both cases i can use the Xwindows graphic interface. It seems there is no diff. whether X11Forward is set or not. Did i miss something??

[Jerome Baron]

Hi,

For me the only way to disable X11 is to put no at X11Forwarding. I try on m??y system and have the same result (graphical application run in all case.
I suspect a "bug".

Regards,
Jerome

[Christian Gebhardt]

Hi

if you have
X11Forwarding yes
in the sshd_config file (don't forget to restart the sshd after changing the parameter) the sshd set the Variable DISPLAY to something like this:

DISPLAY=:10.0

you do not have to set the display manually, all X11-windows are forwarded to your client automatically.

If the ssh-Server is behind a firewall
xterm -display :0
doesn't work
but with X11forwarding enabled and typing
xterm
the display is tunneled via the ssh-connection

Chris

[YLTan]

Hi Christian,

Does this means with X11Forward enable, the Xwindows traffic actually forced to use SSH connection which is encrypted?

Without X11Forward enable, Xwindows traffic are travelling in CLEAR TEXT even I am connecting to the SSH server using SSH client and have the DISPLAY=:10.0

[Christian Gebhardt · Accepted solution]

yes