netdev - Re: bug in tcp?

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Date:	Mon, 16 Apr 2007 15:50:38 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Sebastian Kuzminsky <seb@...hlab.com>
Cc:	netdev@...r.kernel.org
Subject: Re: bug in tcp?

On Mon, 16 Apr 2007 16:28:22 -0600
Sebastian Kuzminsky <seb@...hlab.com> wrote:

> I'm seeing some weird behavior in TCP.  The issue is perfectly
> reproducible using netcat and other programs.  This is what I do:
> 
>     1.  Open a TCP connection over the loopback (over IPv4).
> 
>     2.  Send a couple of bytes of data each way.  No problems.
> 
>     3.  Wait about 120 hours with no writes on either side of the
>         connection.
> 
>     4.  write() a few bytes to the server's socket.  I'd expect the data
>         to go through, but it doesnt.  I see the TCP frame from the
>         server to the client, but instead of an ACK, the client sends
>         back a RST.  netstat shows the bytes sitting in the server's
>         socket's send-buffer.
> 
>     5.  write a few bytes to the client's socket.  The server gets
>         these immediately.
> 
>     6.  On the next server-to-client retransmit, the client gets the
>         bytes from the server.  After this, the connection works normally.
> 
> 
> The libpcap capture file is here (only shows steps 4-6):
> 
>     http://highlab.com/~seb/tcp-idleness-bug
> 
> 
> The behavior is reproducible on all kernels I've tried: 2.4.32, 2.6.19.1,
> and 2.6.20.4.  I dont think it's iptables-related, though I'm rerunning
> the tests on a machine without iptables to be sure.  I'll have results
> for you in 120 hours.  ;-)
> 
> 

What server? Some servers do application timeouts.

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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