On 2011-01-22 06:24, Fernando Gont wrote:
> Hi, Bob,
>
> On 21/01/2011 02:20 p.m., Bob Hinden wrote:
>
>>>>> 1. It is RECOMMENDED that source hosts support the flow label
>>>>> by setting the flow label field for all packets of a flow to
>>>>> the same pseudo-random value.
>>>> I do not see a reason to require this.
>>> Probably that could/should be rephrased as:
>>>
>>> 1. It is RECOMMENDED that source hosts support the flow label by
>>> setting the flow label field for all packets of a flow to the
>>> same value. Such value should not be easily predictable by an
>>> off-path attacker.
>> We could also add to this something like: One way to achieve this is with a
>> pseudo-random value.
>
> +1
>
> -- Although if the flowlabels are expected to be unique for each flow
> (as they currently are), then random numbers have a chance for
> collisions, and the approach proposed in draft-gont-flowlabel-security
> is better.
We seem to have agreed that the primary purpose of the flow label is
to facilitate load balancing, which is a statistical process. For that
to work, while minimising reordering, it's required that all packets
of the same flow have the same label (as is clear in 3697 and will be
clear in 3697bis). However, it is NOT required that flow labels
are strictly unique - a birthday-paradox rate of duplicate flow labels
really won't matter. I suggest (and this is a new suggestion that's
been in my mind for a few days) that the uniqueness requirement can and
should be relaxed to 'unique with high probability'.
Brian
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