netdev - Re: [PATCH net] ipv6 addrconf: Implemented enhanced DAD (RFC7527)

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Date:   Mon, 21 Nov 2016 23:46:44 +0100
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Erik Nordmark <nordmark@...ic.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv6 addrconf: Implemented enhanced DAD (RFC7527)

Hi,

On 21.11.2016 18:10, Erik Nordmark wrote:
> On 11/16/16 10:49 PM, Hannes Frederic Sowa wrote:
>> I thought about even removing the sysctl altogether and enable enhanced
>> DAD by default. ;)
>>
>> I am in favor of enabling it by default.
>>
>> But given that there could be broken implementations out there, we
>> should give users a choice and provide.
> OK, I'll make it the default and send out a new version of the patch. I
> was told I should base the patch on net-next instead of linux-stable so
> I'll move it there.

Correct.

>>
>> Could you always generate a nonce in the interface structure? You could
>> check the sysctl in the send and receive path to attach and check the
>> nonce. This has the advantage that you don't need to delete the
>> interface and recreate it to enable/disable enhanced dad on an interface
>> (also you can get away with the loop around get_random_bytes to make
>> sure its value is not zero as we don't depend on a non-zero nonce
>> variable to signal enaling of the feature, see below).
> The nonce is per interface address and not per interface. Furthermore,
> the RFC says that on a retry of DAD the nodes will end up using a
> different nonce implying that even for the same interface address it
> should pick a different nonce for each DAD attempt.
> Note that since there is no automatic retry of DAD (per RFC4862) and
> each try would check the current sysctl setting so I don't think
> pre-generating the nonce would change the behavior.

Sorry for misreading the code then. ;) Indeed, I don't see a problem
with your proposal.

Thanks,
Hannes