Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S945835AbcJaTPj (ORCPT <rfc822;w@1wt.eu>);
        Mon, 31 Oct 2016 15:15:39 -0400
Received: from shards.monkeyblade.net ([184.105.139.130]:56290 "EHLO
        shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S945816AbcJaTPg (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 31 Oct 2016 15:15:36 -0400
Date: Mon, 31 Oct 2016 15:15:34 -0400 (EDT)
Message-Id: <20161031.151534.329043104568805244.davem@davemloft.net>
To: jkbs@redhat.com
Cc: tom@herbertland.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, kuznet@ms2.inr.ac.ru, jmorris@namei.org,
        yoshfuji@linux-ipv6.org, kaber@trash.net
Subject: Re: [PATCH net-next 5/5] ipv6: Compute multipath hash for
 forwarded ICMP errors from offending packet
From: David Miller <davem@davemloft.net>
In-Reply-To: <8760oa9egg.fsf@redhat.com>
References: <CALx6S35qmAwFfK1TNAcJJs1jK7JgM8U4MCh3wC8hkuf2qae+sw@mail.gmail.com>
        <8760oa9egg.fsf@redhat.com>
X-Mailer: Mew version 6.7 on Emacs 24.5 / Mule 6.0 (HANACHIRUSATO)
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Mon, 31 Oct 2016 11:16:01 -0700 (PDT)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 813
Lines: 22

From: Jakub Sitnicki <jkbs@redhat.com>
Date: Sun, 30 Oct 2016 14:03:11 +0100

> 2) ensure the flow labels used in both directions are the same (either
>    reflected by one side, or fixed, e.g. not used and set to 0), so that
>    the 4-tuple we hash over when forwarding, <src addr, dst addr, flow
>    label, next hdr>, is the same both ways, modulo the order of
>    addresses.

Even Linux, by default, does not do reflection.

See the flowlabel_consistency sysctl, which we set by default to '1'.

I think we need to think a lot more about how systems actually set and
use flowlabels.

Also, one issue I also had with this series was adding a new member
to the flow label.  Is it possible to implement this like the ipv4
side did, by simply passing a new parameter around to the necessary
functions?

Thanks.