From owner-freebsd-amd64@FreeBSD.ORG Tue May 12 14:10:33 2009 Return-Path: Delivered-To: freebsd-amd64@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 007DE1065677 for ; Tue, 12 May 2009 14:10:32 +0000 (UTC) (envelope-from michael@rancid.berkeley.edu) Received: from malcolm.berkeley.edu (malcolm.Berkeley.EDU [IPv6:2607:f140:ffff:ffff::239]) by mx1.freebsd.org (Postfix) with ESMTP id D6D0D8FC19 for ; Tue, 12 May 2009 14:10:32 +0000 (UTC) (envelope-from michael@rancid.berkeley.edu) Received: from michaels-macbook-pro.local ([IPv6:2607:f140:800:8001:21f:5bff:feeb:81c6]) (authenticated bits=0) by malcolm.berkeley.edu (8.14.3/8.13.8m1) with ESMTP id n4CEAWpg050233 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 12 May 2009 07:10:32 -0700 (PDT) (envelope-from michael@rancid.berkeley.edu) Message-ID: <4A098357.2020204@rancid.berkeley.edu> Date: Tue, 12 May 2009 07:10:31 -0700 From: Michael Sinatra User-Agent: Thunderbird 2.0.0.21 (Macintosh/20090302) MIME-Version: 1.0 To: Andrey Voitenkov References: <200905121120.n4CBK2bc091671@freefall.freebsd.org> In-Reply-To: <200905121120.n4CBK2bc091671@freefall.freebsd.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: ClamAV 0.94.2/9354/Mon May 11 19:26:05 2009 on malcolm.berkeley.edu X-Virus-Status: Clean X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.0.1 (malcolm.berkeley.edu [IPv6:2607:f140:ffff:ffff::239]); Tue, 12 May 2009 07:10:32 -0700 (PDT) Cc: freebsd-amd64@freebsd.org Subject: Re: amd64/134486: Wrong MSS in outgoing packets for non-default (1460) MSS X-BeenThere: freebsd-amd64@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Porting FreeBSD to the AMD64 platform List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 12 May 2009 14:10:33 -0000 On 5/12/09 4:20 AM, Andrey Voitenkov wrote: > The following reply was made to PR amd64/134486; it has been noted by GNATS. > > From: Andrey Voitenkov > To: bug-followup@FreeBSD.org > Cc: av@holymail.biz > Subject: Re: amd64/134486: Wrong MSS in outgoing packets for non-default > (1460) MSS > Date: Tue, 12 May 2009 13:50:29 +0300 > > Workaround: > ifconfig fxp0 -rxcsum -txcsum -tso > (works for em0 also) I have seen this same problem on i386 with a TSO-capable fxp0 interface. You can also work around the problem with: sysctl net.inet.tcp.tso=0 This issue was mentioned elsewhere on one of the FreeBSD lists, but I can't seem to locate it now. It seems that if TSO is enabled, the system sends packets up to the system's *own* interface MTU-40, ignoring the MSS. After failing to received a delayed ACK, the system drops back to the correct frame size, but the resulting delay makes the connection really slow. Like I said, I can reproduce this behavior on an i386 system with a TSO-capable fxp interface and can send tcpdump output very similar to Andrey's if needed. michael