From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B7844C4360F for ; Fri, 5 Apr 2019 00:44:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 823742171F for ; Fri, 5 Apr 2019 00:44:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730086AbfDEAoU convert rfc822-to-8bit (ORCPT ); Thu, 4 Apr 2019 20:44:20 -0400 Received: from shards.monkeyblade.net ([23.128.96.9]:55454 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729697AbfDEAoU (ORCPT ); Thu, 4 Apr 2019 20:44:20 -0400 Received: from localhost (unknown [IPv6:2601:601:9f80:35cd::d71]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 75518147386CD; Thu, 4 Apr 2019 17:44:19 -0700 (PDT) Date: Thu, 04 Apr 2019 17:44:19 -0700 (PDT) Message-Id: <20190404.174419.1813732301965311345.davem@davemloft.net> To: olivier.tilmans@nokia-bell-labs.com Cc: research@bobbriscoe.net, koen.de_schepper@nokia-bell-labs.com, edumazet@google.com, kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next] tcp: Accept ECT on SYN in the presence of RFC8311 From: David Miller In-Reply-To: <20190403134915.6616-1-olivier.tilmans@nokia-bell-labs.com> References: <20190403134915.6616-1-olivier.tilmans@nokia-bell-labs.com> X-Mailer: Mew version 6.8 on Emacs 26.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=iso-8859-1 Content-Transfer-Encoding: 8BIT X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Thu, 04 Apr 2019 17:44:19 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Tilmans, Olivier (Nokia - BE/Antwerp)" Date: Wed, 3 Apr 2019 13:49:42 +0000 > Linux currently disable ECN for incoming connections when the SYN > requests ECN and the IP header has ECT(0)/ECT(1) set, as some > networks were reportedly mangling the ToS byte, hence could later > trigger false congestion notifications. > > RFC8311 §4.3 relaxes RFC3168's requirements such that ECT can be set > one TCP control packets (including SYNs). The main benefit of this > is the decreased probability of losing a SYN in a congested > ECN-capable network (i.e., it avoids the initial 1s timeout). > Additionally, this allows the development of newer TCP extensions, > such as AccECN. > > This patch relaxes the previous check, by enabling ECN on incoming > connections using SYN+ECT if at least one bit of the reserved flags > of the TCP header is set. Such bit would indicate that the sender of > the SYN is using a newer TCP feature than what the host implements, > such as AccECN, and is thus implementing RFC8311. This enables > end-hosts not supporting such extensions to still negociate ECN, and > to have some of the benefits of using ECN on control packets. > > Signed-off-by: Olivier Tilmans > Suggested-by: Bob Briscoe Applied, thanks.