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

[Brett Parker]

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 :)

> 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 :)

Cheers,
-- 
Brett Parker