how tunnel X11 to a slow system?

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Currently I have two systems, A and B, where B is a pretty slow system.

When I connect from A to B without tunnelling X11, then when I export
the DISPLAY to A everything is ok.

But if I enable X11 tunneling when I connect to B, then the tunnelled X
applications are running way too slow.  I assume its because B is not
powerfull enough to handle the encryption of the X11 protocol.

So I was thinking maybe I could use a 3rd system, which has a fast CPU.
  Lets call this system "C". (C would be on the same side of the
firewall as B)

Then what I would like to do is to do a SSH connection from A to C with
X11 tunneling.  This will get me past the firewall.  Then I would like
to do a SSH connection between C and B, without tunneling.  That way,
the slow system B will not have to do any encryption when exporting the
DISPLAY.  Then starting an X application on B would show up on A.  The
X11 packets would go through the 2 ssh connections, but only encrypted
between A and C.

Is this possible?

I tried doing the following but it didn't work:

A $ ssh -X C

C $ xhost + B
C $ ssh -x B  (note the lowercase x to disable X11 forwarding...)

B $ export DISPLAY=C
B $ xclock


Re: how tunnel X11 to a slow system?

Before you try some confusing scenario, try running SSH on system B
with the -C option.  This will compress the data before it is sent

Also realize that X apps can be very network intensive and the speed
of your network can be the limiting factor here.

You may say, but we have a 100 MB network on a GB backbone.  That may
be true, but your network guys may be limiting your port to 10 MB,
slowing you down.  

Re: how tunnel X11 to a slow system?

Thanks for the advice.

I did try the -C option, with no significant improvement in performance.

I also did try a faster cipher, like blowfish... same thing.

The reason why I suspect that is not related to network speed is that as
soon as I don't tunnel X11 then everything becomes much faster. I
beleive this rules out the network speed issue, unless the encrypting
adds a lot to the original data.

B is a Mips r5000 180 Mhz with 512M of ram, running OpenSSH_3.0.1p1.  I
would think that 180Mhz would be enough to handle the SSH encryption but
the more testing I do, the more it looks like a CPU issue.

Thanks for the feedback,

tyler wrote:
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