Re: TCP Window Scaling problem with buggy routers FIX works

[Stephen Hemminger]

On Mon, 30 Aug 2004 13:00:37 +0200
Maciej Soltysiak <solt@xxxxxxxxxxxxxxxxx> wrote:

> Hi,
> 
> I am just letting you guys know that the fix for
> tcp window scaling problem with buggy routers works.

As mentioned in the patch to automatically manage tcp window
scale size. This was an (mostly unwanted) side-effect.

> There were people (including me) reporting that tcp traffic
> through some buggy (eg. cisco) routers in linux-2.6.8 slows
> down to a crawl.

Find and fix the problem. It may come back.

> A workaround was to zero tcp_window_scaling sysctl knob.
> 
> With this patch:
> http://www.kernel.org/pub/linux/kernel/v2.5/testing/cset/cset-shemminger@xxxxxxxx|ChangeSet|20040826205608|22084.txt
> 
> sitting in 2.6.9-rc1 BK repository the linux box can have
> fast transfers again.
> 
> Note that they are not that fast as with tcp_window_scaling disabled.
> But they are certainly fast and will not cause problems like
> ssh sessions hangning, etc.

That is because every time the linux box says the window size is N.
The other side is thinking the window is N/4 because the router in
the middle corrupted the initial connection requuest.


> Thanks for the workaround for buggy routers netdev!

Don't expect the default Linux kernel configuration to work
on broken networks.


-- 
Stephen Hemminger 		mailto:shemminger@xxxxxxxx
Open Source Development Lab	http://developer.osdl.org/shemminger
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