Re: Alexey Melnikov's No Objection on draft-ietf-6man-ra-pref64-08: (with COMMENT)

["Alexey Melnikov" <[e-mail]>]

Hi Jen,

On Tue, Dec 17, 2019, at 3:18 AM, Jen Linkova wrote:
> Hi Alexey,
> 
> On Tue, Dec 17, 2019 at 12:25 AM Alexey Melnikov via Datatracker
> <[e-mail]> wrote:
> >    Lifetime seconds over which this NAT64 prefix MAY be used. The value
> >             of the Scaled Lifetime field SHOULD by default be set to the
> >             lesser of 3 x MaxRtrAdvInterval divided by 8, or 8191. The
> >             receiver MUST multiply the Scaled Lifetime value by 8 (for
> >             example, by logical left shift) to calculate the maximum
> >             time in seconds the prefix MAY be used. Lifetime of 0
> >             indicates that the prefix SHOULD NOT be used anymore. Router
> >             vendors SHOULD allow administrators to specify non-zero
> >             lifetime values which are not divisible by 8. In such cases
> >             the router SHOULD round the provided value up to the lesser
> >             of nearest integer divisible by 8, or 65528 and divide the
> >             result by 8 (or just perform a logical right-shift by 3) and
> >             set the Scaled Lifetime field to the resulting value. If
> >             such a non-zero lifetime value to be divided by 8 (to be
> >             subjected to a logical right-shift by 3) is less than 8 then
> >             the Scaled Lifetime field SHOULD by default be set to 1.
> >
> > I found this description to be unclear. You are first saying to round the value
> > up, but then your last sentence looks like a special case, where it is not
> > supposed to be according to my understanding of the meaning of "round up". I
> > suggest this text needs more work.
> 
> Would it be more clear if the one more sentence is added to that paragraph:
> 
> "If  such a non-zero lifetime value to be divided by 8 (to be
>   subjected to a logical right-shift by 3) is less than 8 then
>  the Scaled Lifetime field SHOULD be set to 1.

I would change this to read:

  "For example, if  such a non-zero lifetime value to be divided by 8 (to be
  subjected to a logical right-shift by 3) is less than 8 then
  the Scaled Lifetime field is set to 1.

I.e. values <8 are a special case of "rounding up".

> This is done to ensure that non-zero lifetime is always encoded as
> non-zero Scaled Lifetime."

This is a helpful addition.

Best Regards,
Alexey