From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765784AbXG2PbB (ORCPT ); Sun, 29 Jul 2007 11:31:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762617AbXG2Pav (ORCPT ); Sun, 29 Jul 2007 11:30:51 -0400 Received: from adsl-67-120-171-161.dsl.lsan03.pacbell.net ([67.120.171.161]:45868 "HELO linuxace.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1763028AbXG2Pau (ORCPT ); Sun, 29 Jul 2007 11:30:50 -0400 Date: Sun, 29 Jul 2007 08:30:49 -0700 From: Phil Oester To: "Darryl L. Miles" Cc: linux-kernel@vger.kernel.org Subject: Re: TCP SACK issue, hung connection, tcpdump included Message-ID: <20070729153049.GA13309@linuxace.com> References: <46AC2CBE.5010500@netbauds.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46AC2CBE.5010500@netbauds.net> User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 29, 2007 at 06:59:26AM +0100, Darryl L. Miles wrote: > The problems start around time index 09:21:39.860302 when the CLIENT issues > a TCP packet with SACK option set (seemingly for a data segment which has > already been seen) from that point on the connection hangs. I'd say most likely scenario is the SERVER is behind a Cisco Pix firewall, which has known bugs in handling packets with sack option. By default the Cisco has sequence number randomization enabled, but it's a half-assed implementation which doesn't bother adjusting the sequence numbers inside sack options. This has been reported to Cisco, and they don't seem to care. As a workaround, you can do this: echo 0 > /proc/sys/net/ipv4/tcp_sack and it will probably fix it up. It'd be really nice, however, to have a per-route option for sack, similar to how we can clamp window scaling per route. Something like the below ip r a Phil