netdev - Re: TCP RESET after SACK in Kernel 2.6

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Message-Id: <20081016.014057.122319113.davem@davemloft.net>
Date:	Thu, 16 Oct 2008 01:40:57 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	cs-linuxnet@...warz-online.com
Cc:	linux-net@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: TCP RESET after SACK in Kernel 2.6

From: Christian Schwarz <cs-linuxnet@...warz-online.com>
Date: Thu, 16 Oct 2008 10:36:57 +0200

[ netdev is the place to post if you actually want a
  knowledgable person to look into your problem ]

> We're running a Debian Linux router with masquerading enabled
> to access a customers site.  The customer connection has a lot of
> packet loss, so we receive some TCP SACK-messages.
> 
> Our old system with Debian 3.1 and Kernel 2.4.xx handled this correctly,
> but after upgrading to Debian 4.0 and Kenrel 2.6.26.5, sometimes the
> SACK-queries are answered with a TCP RESET by the kernel.

Without any example tcpdump traces it is impossible for anyone to help
debug this problem.

> Background question: we have the following setup:
> 
>    client host  ->  router w/ masquerading  ->  target host
> 
> When the target host sends a SACK-query, is it the router's job to
> resend the packets or is this the client host's job?

The end node TCP stack does this, the router doesn't do this.
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