[ALUG] Re: Re: Re: Re: TCP Problem *NOT* routing (was: Wierd routing/DNS problem)

[cl at isbd.net]

On Fri, Oct 06, 2006 at 09:57:53AM +0100, Brett Parker wrote:
> On Fri, Oct 06, 2006 at 09:47:50AM +0100, cl at isbd.net wrote:
> > On Fri, Oct 06, 2006 at 09:40:09AM +0100, Brett Parker wrote:
> > > OK - alarm bells just went off in my head... just a simple, really easy
> > > question here... is this a 2.6.17 kernel? If so, can you try the
> > > following:
> > >         echo 0 > /proc/sys/net/ipv4/tcp_window_scaling
> > > 
> > It's a 2.6.18 kernel (rc5 I think), but the above *does* fix the
> > problem - what arcane art is that?!   :-)
> > 
> > Brilliant, thanks.
> 
> OK - the basic problem is that in the 2.6.17 kernel the window scaling
> was actually "fixed" to conform to the specification, and now uses a
> percentage of available ram for the window sizes... the unfortunate part
> is that half the routers in the world are completely broken wrt the
> spec, which is a pain...
> 
> So, the "long term" fix for now is to add to /etc/sysctl.conf the
> following:
> 
> net.ipv4.tcp_rmem=4096 87380 174760
> net.ipv4.tcp_wmem=4096 16384 131072
> 
> Which are the old defaults for the window sizes.
> 
> To test that you can do:
>         sysctl -w net.ipv4.tcp_rmem="4096 87380 174760"
>         sysctl -w net.ipv4.tcp_wmem="4096 16384 131072"
>         sysctl -w net.ipv4.tcp_window_scaling=1
> 
> If you want to check that these are set, cat the corresponding files in
> /proc/sys, so for example:
>         cat /proc/sys/net/ipv4/tcp_window_scaling
> 
> And check that's back to 1, and the other 2 are set as I've put in
> here... and long live the tcp connection :)
> 
Excellent, thank you, I've done all that now and I'm just doing a
reboot remotely - I'm not totally convinced it'll come back up for me
to check now but that doesn't really matter.


> > I'm expecting this sort of problem really, I'm pushing the edge of
> > drivers available in Linux which is why I'm using a 2.6.18 kernel, the
> > SuSE 10.2 alpha (it'll be beta very soon I think) was one of the few
> > that has the drivers I want in it.
> 
> I'm fairly sure that 2.6.18 has been released, Noodles probably knows
> better than I... *looks at kernel.org* - yup, it's been released,
> 2006-09-20 was the release date :)
> 
Yes, I know that, but there's no distribution with the released
version of the 2.6.18 kernel in it yet - at least not a 'major'
distribution.  I need to get something up and running in order to
enable me to build a released 2.6.18 kernel.

While I've been waffling away here the system *has* rebooted
successfully and now I can make TCP connections to the outside world!

:-)   Thanks very much indeed.

-- 
Chris Green (chris at halon.org.uk)