From: Nicolas Dichtel <nicolas.dichtel@6wind•com>
To: "Bjørn Mork" <bjorn@mork•no>
Cc: David Miller <davem@davemloft•net>,
netdev@vger•kernel.org, yoshfuji@linux-ipv6•org
Subject: Re: [PATCH net-next] ip6_tunnel: ensure to always have a link local address
Date: Wed, 21 Aug 2013 14:11:51 +0200 [thread overview]
Message-ID: <5214AE87.7060104@6wind.com> (raw)
In-Reply-To: <8761uz6zra.fsf@nemi.mork.no>
Le 21/08/2013 13:37, Bjørn Mork a écrit :
> Nicolas Dichtel <nicolas.dichtel@6wind•com> writes:
>
>> Le 21/08/2013 11:02, Bjørn Mork a écrit :
>>> Nicolas Dichtel <nicolas.dichtel@6wind•com> writes:
>>>> Le 21/08/2013 08:48, David Miller a écrit :
>>>>
>>>>> 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 generated
>>>>> 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
>> interface, because it's statically configured and there is a limited
>> number of interfaces.
>>
>> For virtual interfaces, they can be dynamically created and destroyed
>> by daemons and we can have a lot of interfaces. Hence it could be hard
>> to fix them.
>
> If they are created by daemons then it should be up to the daemons to
> fix them. Or?
>
>> Trying to avoid these errors at kernel level could be useful.
>
> I strongly believe in fixing configuration issues in userspace if at all
> possible. You are setting a new policy every time you implement an
> automatic fix or workaround. It is so much better to keep that out of
> the kernel, or the next question you will face is "How do I change this
> policy? I want the addresses to be assigned by function Y"
>
> I see no reason why the daemon creating these interfaces can't also
> fixup any collisions. Or maybe better: If your daemon create millions
> of interfaces, and cares about unique addresses, then it should
> implement it's own address management.
Ok ok, you convince me ;-)
I will wait David feedback.
>
>> I've start to write a patch, and to test it I've just run a simple
>> test which generate 1 000 000 of random addresses. I've run it several
>> times (maybe not enough ;-)) and I never get a duplicated address...
>
> Well, there are only 2^46 combinations so you are guaranteed to hit a
> collision if you just generate 70 368 744 177 665 random addresses :-)
Yes, it was just to say that the function which generate these addresses has a
"good" entropy ;-)
prev parent reply other threads:[~2013-08-21 12:11 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-20 10:16 [PATCH net-next] ip6_tunnel: ensure to always have a link local address Nicolas Dichtel
2013-08-21 6:48 ` David Miller
2013-08-21 7:40 ` Nicolas Dichtel
2013-08-21 9:02 ` Bjørn Mork
2013-08-21 10:25 ` Nicolas Dichtel
2013-08-21 11:37 ` Bjørn Mork
2013-08-21 12:11 ` Nicolas Dichtel [this message]
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