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

[Brian E Carpenter <[e-mail]>]

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.

   Brian