From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp108.iad3a.emailsrvr.com (smtp108.iad3a.emailsrvr.com [173.203.187.108]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 9C8DA3CB36 for ; Mon, 12 Aug 2019 20:49:56 -0400 (EDT) Received: from smtp22.relay.iad3a.emailsrvr.com (localhost [127.0.0.1]) by smtp22.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 6FF6C5EA1; Mon, 12 Aug 2019 20:49:56 -0400 (EDT) X-SMTPDoctor-Processed: csmtpprox beta DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=g001.emailsrvr.com; s=20190322-9u7zjiwi; t=1565657396; bh=oBqMlX1Zd6+Jw8TUtRxKjTsN9fM78FK8ngT/nBmzJVc=; h=Date:Subject:From:To:From; b=bSPavjFD9coa3H0u6i2iXWHnMgaZ2Fxq3kyyi2KPmsSi48ALTxnjryE3SMSizNgDN d4J9d3QoCx0F2LiFDrEQJm8lofnw+ZQSRtXUX+cjARm59YL8CW1en51X5s5Tju6MTo 5iFRuK+h9+5N9+K/XoPv5m2Ljx50na8YKQncF2D0= Received: from app68.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by smtp22.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 4B036453B; Mon, 12 Aug 2019 20:49:56 -0400 (EDT) X-Sender-Id: dpreed@deepplum.com Received: from app68.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by 0.0.0.0:25 (trex/5.7.12); Mon, 12 Aug 2019 20:49:56 -0400 Received: from deepplum.com (localhost.localdomain [127.0.0.1]) by app68.wa-webapps.iad3a (Postfix) with ESMTP id 3816EE00FE; Mon, 12 Aug 2019 20:49:56 -0400 (EDT) Received: by apps.rackspace.com (Authenticated sender: dpreed@deepplum.com, from: dpreed@deepplum.com) with HTTP; Mon, 12 Aug 2019 20:49:56 -0400 (EDT) X-Auth-ID: dpreed@deepplum.com Date: Mon, 12 Aug 2019 20:49:56 -0400 (EDT) From: "David P. Reed" To: "Jonathan Morton" Cc: "Dave Taht" , "ECN-Sane" MIME-Version: 1.0 Content-Type: text/plain;charset=UTF-8 Content-Transfer-Encoding: quoted-printable Importance: Normal X-Priority: 3 (Normal) X-Type: plain In-Reply-To: References: Message-ID: <1565657396.226529457@apps.rackspace.com> X-Mailer: webmail/16.4.7-RC Subject: Re: [Ecn-sane] cautionary tcp tale X-BeenThere: ecn-sane@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Discussion of explicit congestion notification's impact on the Internet List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 13 Aug 2019 00:49:56 -0000 This is the stupidity of NAT, which encouraged modifying TCP checksums, whi= ch are supposed to be not modified in the network at all.=0A=0AThe whole po= int of an "end-to-end" checksum is that the middle shouldn't touch it!=0A= =0ANow I get why NAT became popular, though at the time many of us pretty m= uch vomited all over the idea as completely bogus.=0A=0AI do worry that now= there is TCP checksum offloading in NICs, that middleboxes are feeling fre= er just to throw away and recalculate checksums as they pass through, and n= ot bother to forward non-TCP, nonUDP, nonICMP IP packets at all.=0A=0AThis = would be the kind of thing that Cisco, for example, might just do, since th= ey have long thought that they owned the Internet design as a corporate ent= ity.=0A=0A=0AOn Monday, August 12, 2019 7:37pm, "Jonathan Morton" said:=0A=0A>> On 13 Aug, 2019, at 12:30 am, Dave Taht wrote:=0A>>=0A>> https://www.snellman.net/blog/archive/2017= -07-20-s3-mystery/=0A> =0A> TL;DR summary:=0A> =0A> Buggy checksum recalcul= ation in a cable modem caused minor packet loss (through=0A> rejection at t= he receiver). In the absence of TCP Timestamps, the retransmissions=0A> of= these lost packets were identical and triggered the same bug. Result,=0A>= connections to certain particular servers which had the unusual property o= f=0A> disabling TCP Timestamps would quickly stall.=0A> =0A> I think a tool= could be made to watch a sample of received traffic for this=0A> pattern: = incorrect checksums where the correct checksum is the same each time=0A> (t= hough different per deployment). How much network equipment exhibits this = bug?=0A> =0A> - Jonathan Morton=0A> ______________________________________= _________=0A> Ecn-sane mailing list=0A> Ecn-sane@lists.bufferbloat.net=0A> = https://lists.bufferbloat.net/listinfo/ecn-sane=0A> =0A