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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 <davem@davemloft.net>
In-Reply-To: <20190403134915.6616-1-olivier.tilmans@nokia-bell-labs.com>
References: <20190403134915.6616-1-olivier.tilmans@nokia-bell-labs.com>
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From: "Tilmans, Olivier (Nokia - BE/Antwerp)" <olivier.tilmans@nokia-bell-labs.com>
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 <olivier.tilmans@nokia-bell-labs.com>
> Suggested-by: Bob Briscoe <research@bobbriscoe.net>

Applied, thanks.