Re: TCP connection stalls under 2.6.24.7

[Thomas Jarosch <thomas.jarosch@intra2net.com>]

On Thursday, 17. July 2008 15:55:25 Ilpo Järvinen wrote:
> It would quite interesting to know more details about the mail server and
> why the duplicate ACKs are not generated or don't ever reach the sender
> but I guess the details are out of reach?

It will be quite difficult to get more details as it's the SMTP relay sever
of Germany's biggest ISP. There's a comment about them
in Patrick's blog from 2008-06-23 if you are curious ;-)

We see the same issue with a MX server from "United Internet".
Normally they are pretty accurate about standards (they run GMX),
so I guess this must be a problem of a router in between.

This is also supported by the fact that 935 of our boxes already updated
to kernel 2.6.24.7, yet the problem occured only at three sites and I guess
there are more people out there using that SMTP relay server.

Could you somehow "probe" the servers to see if they normally
send duplicated ACKs by faking/forcing a retransmission?
Though I guess this would invole writing some TCP "test" code.

> One option would be to disable reentry to FRTO when some progress was
> made... Please try with the patch below...

Thanks for the patch. It seemed to help a bit. Here are two more traces:
http://www.intra2net.com/de/download/tcpdump/tcp_frto_with_patch.tar.bz2

The first connection somehow made it after 400 seconds,
the second one stalled and timed out :-(
Hope they dumps are useful to you.

Chers,
Thomas
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