Date: Fri, 7 Feb 2003 08:49:36 -0500 (EST)
From: "Richard B. Johnson" <root@chaos.analogic.com>
Reply-To: root@chaos.analogic.com
To: Martin Zielinski <mz@seh.de>
cc: linux-kernel@vger.kernel.org
Subject: Re: TCP Connection times out
In-Reply-To: <200302071430.34001.mz@seh.de>
Message-ID: <Pine.LNX.3.95.1030207083742.28526B-100000@chaos.analogic.com>
MIME-Version: 1.0
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On Fri, 7 Feb 2003, Martin Zielinski wrote:

> Hello,
> I'm not on the list, so I'm not really informed what's going on. But...
> 
> our problem is a network printer the has paper empty.
> The socket connection to the printer broke down after ~45 minutes with
> errno 110 (Connection timed out).
> 
> Linux base version is 2.4.18 on a strongarm machine.
> 
> Tracking this down brought us to the tcp_send_probe0 function in 
> net/ipv4/tcp_output.c.
> The tp->backoff value becomes allways increased.
> on this machine from 31 on  (tp->rto << tp->backoff) is 0.
> 
> The xmit timer is set to this timeout value - resulting in an ACK burst.
> If the TCP sender gets the (default) 16 ACKS out, before the receiver can 
> answer them, the connection dies.
> This happened every night, when the printer received a huge job from a
> foreign  office.
> 
> If this isn't a bug, it should be made configurable. Or do we miss something?
> 
> Thanks.

Get new firmware for your printer. It's broken. The connection
timed out because the connection timed out, i.e., when the printer
is out of paper, it refuses to ACK incoming packets. You do not
modify a standard TCP/IP implementation to fix a broken printer.

The printer is expecting to hold-off incoming network data, by
refusing to ACK it, until someone adds more paper. This is
unconsionable behavior that violates any standards of Engineering
practice. There is no time-out you could increase because the
printer may be out-of-paper forever, i.e., somebody needs to go
buy some. Network-connected devices just can't do things this
way. The name of the vendor should be published and the vendor
"educated" in such a way that no such printers remain connected
to a network until they are fixed.

And, if Linux didn't follow the standard, and let dead "connected"
devices remain in a connected state, servers that use connections
would would become impossible.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.


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