From owner-freebsd-transport@freebsd.org Fri Jan 19 19:16:20 2018 Return-Path: Delivered-To: freebsd-transport@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 7259EEC2D83 for ; Fri, 19 Jan 2018 19:16:20 +0000 (UTC) (envelope-from pkelsey@gmail.com) Received: from mail-pf0-x234.google.com (mail-pf0-x234.google.com [IPv6:2607:f8b0:400e:c00::234]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 42A9870227 for ; Fri, 19 Jan 2018 19:16:20 +0000 (UTC) (envelope-from pkelsey@gmail.com) Received: by mail-pf0-x234.google.com with SMTP id e76so2066090pfk.1 for ; Fri, 19 Jan 2018 11:16:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:sender:in-reply-to:references:from:date:message-id :subject:to; bh=JFf1DGX7dI4QteRpbEf8uMNSRt9AToQPWi+2rm/g52c=; b=Sy2Gvdxkxgh4RqEJ7F3C6iiri1aJqDhelI5kEVV3diPOlzGddPzdV3im+l7pLsGN9s 7IpLLUwiaU4TqOFsrPRBF7fIxIXK0vuorgvwS8xAhFaZP3gVpumxuUutEanqT8qFLCUa 06D9sNyhx9GxUCFzWXj9YhD/jLA5WgNSjxsagq+jV6w6jRH2uDWrdCIWVOHouHXUb0lK Xbt2zEzT+XMR/VlgWiVa8Hytz85KnJS0VpLUa+yJUYQeHCpkADzOC2j2hNNV0a7xAptZ ZluPRfTWuIM9ifTRtyi3ln9egQOPAh6cIXEeB6lRS6hRzSy6REXCvg1c0jHJ0F7Tqo0s 7gUQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:sender:in-reply-to:references:from :date:message-id:subject:to; bh=JFf1DGX7dI4QteRpbEf8uMNSRt9AToQPWi+2rm/g52c=; b=oznw+LhfFI1gjNVJkpIMzZhFEIfS60XYARdLGYFG0/dvSg5efjJGQ26NvGQpRaf1L9 Nt/FlURlK4MRUAH/8Dksd3oxfsSaf5ZpMYbsbOuXyBcATHUqfb3lK/sRznCCIVRXe4+l Rm5L1X8ke1jOglBeXIO7WIrVwKkDby7PyFrKgthbmjc3VMJ61NwPK5+qLqzpEDke67KS 1Nero7NmDFDu2aHgz5iWuYLGmxw3ol2yt3I75gGdq+jXvGSOuBjf79sgflLUfWXK8d7B mmA9V0I5Qx5UrB+7B7cnJlerS7K8FT0d3bsHqfH/K57bIGpI6WkvjNUyhB/xs7PqYp9N Viuw== X-Gm-Message-State: AKwxyte6cso90gNIR4Ip5mGRKAHfvdoAVsezW+97FX6CVTH37/bF8yEB swLsXgskGuW7pXuN6a7R4qjoNw6LSlrc0qvzZHWxdw== X-Google-Smtp-Source: ACJfBosHxrMC8HdzOJ83b+ne8xrH4sVbqpGS9VTb8L15dhI3rHuIEVVJ1b45Pydf/1AT0joxh+VNo5GGzAL8Hx6JM6I= X-Received: by 10.99.113.75 with SMTP id b11mr32992842pgn.271.1516389379337; Fri, 19 Jan 2018 11:16:19 -0800 (PST) MIME-Version: 1.0 Sender: pkelsey@gmail.com Received: by 10.236.156.17 with HTTP; Fri, 19 Jan 2018 11:16:18 -0800 (PST) In-Reply-To: <2AE83CF2-FF6D-4849-AEB9-7FCCA43613A9@freebsd.org> References: <2AE83CF2-FF6D-4849-AEB9-7FCCA43613A9@freebsd.org> From: Patrick Kelsey Date: Fri, 19 Jan 2018 14:16:18 -0500 X-Google-Sender-Auth: hZ9CB-kda7aX65bkqaOy223AAjA Message-ID: Subject: Re: TCP Fast Open Linux behaviour To: freebsd-transport@freebsd.org Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.25 X-BeenThere: freebsd-transport@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: Discussions of transport level network protocols in FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 19 Jan 2018 19:16:20 -0000 On Wed, Jan 17, 2018 at 4:55 PM, Michael Tuexen wrote: > Dear all, > > at the last Telco the following question was raised: > > When Linux is acting as TCP client using TCP fast open, > does it accept user data sent with the SYN-ACK. > > I tested it with the Linux kernel 4.9.77, which is the current > LTS release and figured out that the data sent with the SYN-ACK > is accepted. See the attached .pcapng file. > > The current Ubuntu 17.10 using the kernel 4.13.0 shows the > same behaviour. > > > Michael, Thank you for performing this test with recent Linux kernels and finding that the issue where the Linux TFO client-side implementation would not ACK data in a SYN-ACK has been resolved. The issue did exist at one time, going back to at least the 4.4 kernel, as highlighted during testing of my TFO server-side implementation by multiple parties. One person involved in that testing elicited an explanation from Yuchung Cheng as to why the flaw in the Linux TFO client-side implementation existed: https://www.ietf.org/mail-archive/web/tcpm/current/msg10175.html I will still need to add a knob to the FreeBSD TFO server-side implementation to enable a workaround mode that doesn't send data in TFO SYN-ACKs when data is available, but instead immediately chases the SYN-ACK with a data segment, so that service providers that want to provide good TFO performance for fielded broken Linux clients can do so. -Patrick