[X2Go-Dev] Traffic shaping nightmare - missing SSH TOS bits

[John A. Sullivan III]

On Tue, 2012-02-21 at 08:41 +0100, Oleksandr Shneyder wrote:
> Am 21.02.2012 07:05, schrieb John A. Sullivan III:
> > Hello, all.  I've been working on a project to implement traffic shaping
> > to conform to 95th percentile billing including our X2Go virtual
> > desktops.  One of the challenges is prioritizing the interactive X2Go
> > traffic (screen, keyboard, mouse) differently from bulk traffic like
> > local share transfers, printing, and possibly sound.  I thought this
> > would be trivial because of the SSH transport since SSH sets the
> > minimize-delay bit for interactive traffic and the maximize-throughput
> > bit for bulk transfers.  Thus we could distinguish the packets by
> > looking at the TOS bits.  This is how the default Linux pfifo_fast qdisc
> > does it anyway.
> > 
> > I took a packet trace just to confirm it and, to my horror, I see that
> > we are not setting any of the TOS bits and thus not prioritizing
> > interactive traffic even with the default traffic shaping.
> > 
> > I'm guessing this is a casualty of moving to libssh.  Is there any way
> > to set the TOS bits for interactive to 0x10, bulk to 0x08 as it is in
> > OpenSSH?.  It would be really nice if sound could be configured either
> > way according the the administrator's preference.  Unfortunately, I did
> > not see anything in the libssh documentation to show how to do this
> > although I do not claim to understand it.
> > 
> > This is a critical issue for any WAN based deployments like ours.
> > Thanks - John
<snip>
> Hello John,
> 
> I think it is a question for libssh mailing list.
<snip>
Yes, but the X2Go devs would need to implement the answer in X2Go or, if
it is not possible using libssh, find another way to distinguish the
traffic.  In fact, as I think about it, I wonder if it is unwise to rely
upon libssh for those installation which may not use ssh as a transport
- John