From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Subject: Re: [PATCH net-next] ip6_tunnel: ensure to always have a link local
 address
Date: Wed, 21 Aug 2013 12:25:19 +0200
Message-ID: <5214958F.1080907@6wind.com>
References: <1376993766-5723-1-git-send-email-nicolas.dichtel@6wind.com> <20130820.234818.2230621827416764963.davem@davemloft.net> <52146EE9.1060101@6wind.com> <87haej76wz.fsf@nemi.mork.no>
Reply-To: nicolas.dichtel@6wind.com
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8;
	format=flowed
Content-Transfer-Encoding: QUOTED-PRINTABLE
Cc: David Miller <davem@davemloft.net>, netdev@vger.kernel.org,
	yoshfuji@linux-ipv6.org
To: =?UTF-8?B?QmrDuHJuIE1vcms=?= <bjorn@mork.no>
Return-path: <netdev-owner@vger.kernel.org>
Received: from mail-we0-f178.google.com ([74.125.82.178]:32913 "EHLO
	mail-we0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751487Ab3HUKZW (ORCPT
	<rfc822;netdev@vger.kernel.org>); Wed, 21 Aug 2013 06:25:22 -0400
Received: by mail-we0-f178.google.com with SMTP id u54so233921wes.9
        for <netdev@vger.kernel.org>; Wed, 21 Aug 2013 03:25:20 -0700 (PDT)
In-Reply-To: <87haej76wz.fsf@nemi.mork.no>
Sender: netdev-owner@vger.kernel.org
List-ID: <netdev.vger.kernel.org>

Le 21/08/2013 11:02, Bj=C3=B8rn Mork a =C3=A9crit :
> Nicolas Dichtel <nicolas.dichtel@6wind.com> writes:
>> Le 21/08/2013 08:48, David Miller a =C3=A9crit :
>>
>>> Applied, but this brings up an issue I keep noticing.
>>>
>>> We talk about eth_random_addr() and "uniqueness" together all the
>>> time, but the former never implies the latter.
>>>
>>> And we're going to run into situations where any conflicts generate=
d
>>> by this random address generater will cause reall failures.
>>>
>>> Therefore we'll have to create a system to prevent them.  Probably
>>> using some simple table that keeps track of the addresses we've
>>> generated.
>>>
>> Ok, I will look at this.
>
> Are eth_random_addr() collisions really any different than interfaces
> having the same address for other reasons?
I would tend to say yes, it's different.
It's easy for an administrator to fix a configuration for a physical in=
terface,=20
because it's statically configured and there is a limited number of int=
erfaces.

=46or virtual interfaces, they can be dynamically created and destroyed=
 by daemons=20
and we can have a lot of interfaces. Hence it could be hard to fix them=
=2E Trying=20
to avoid these errors at kernel level could be useful.

I've start to write a patch, and to test it I've just run a simple test=
 which=20
generate 1 000 000 of random addresses. I've run it several times (mayb=
e not=20
enough ;-)) and I never get a duplicated address...