Re: Eric Rescorla's No Objection on draft-ietf-6man-rfc6434-bis-08: (with COMMENT)

[Eric Rescorla <[e-mail]>]

On Tue, Jul 3, 2018 at 8:49 PM, Brian E Carpenter <
[e-mail]> wrote:

> On 04/07/2018 11:19, Eric Rescorla wrote:
> ...
> > S 5.1.
> >>      field as defined in the IPv6 Flow Label specification [RFC6437].
> >>      Forwarding nodes such as routers and load distributors MUST NOT
> >>      depend only on Flow Label values being uniformly distributed.  It
> is
> >>      RECOMMENDED that source hosts support the flow label by setting the
> >>      Flow Label field for all packets of a given flow to the same value
> >>      chosen from an approximation to a discrete uniform distribution.
> >
> > Is there a reason you are using "approximation" here?
> >
>
> RFC6437 says:
>
>    In statistics, a discrete uniform distribution is defined as a
>    probability distribution in which each value in a given range of
>    equally spaced values (such as a sequence of integers) is equally
>    likely to be chosen as the next value.  The values in such a
>    distribution exhibit both variability and unguessability.  Thus, as
>    specified in Section 3, an approximation to a discrete uniform
>    distribution is preferable as the source of flow label values.
>    Intentionally, there are no precise mathematical requirements placed
>    on the distribution or the method used to achieve such a
>    distribution.
>
> [and in Section 3]
>
>    It is therefore RECOMMENDED
>    that source hosts support the flow label by setting the flow label
>    field for all packets of a given flow to the same value chosen from
>    an approximation to a discrete uniform distribution.  Both stateful
>    and stateless methods of assigning a value could be used, but it is
>    outside the scope of this specification to mandate an algorithm.
>
> The reason for saying "approximate" is basically that at least one
> mathematician (my colleague Prof. Cristian Calude) pointed out that
> (apart from quantum processes) there is no way to generate a truly
> random distribution. So you can regard it as mathematical pedantry;
> I have no strong feelings whether that's useful in the present draft.
>

Yeah, I tend to think "approximate" is a bit nitpicky here, but this is a
comment, so I leave it to the author to deal with it as they see fit.

-Ekr


>    Brian
>