Re: [tsvwg] OCS option in draft-ietf-tsvwg-udp-options-07

["C. M. Heard" <[e-mail]>]

On Mon, 11 Mar 2019 19:27:08 +0000 PM Raffaele Zullo wrote:
> On 2019-03-11 16:26, C. M. Heard wrote:
> > On Sat, 9 Mar 2019 11:28:57 -0800 Joe Touch wrote:
> >> Well, there are several implications here:
> >>
> >> 1. we can add in the option length, BUT that also means:
> >>         (a) we need to declare that the option area consumes the
> > whole of
> >>         the surplus area (no chance for other uses)
> >>         OR
> >>         (b) that the surplus area is always zero
> >>         OR
> >>         (c) that OCS covers even the surplus area (it doesn’t need
> > to be
> >>         zero; it does need to be included)
> >>
> >>         we need a choice here. AFAICT, the safest (a)
> >
> > I agree with that.
>
>
> I would add that a Zero padding after UDP Options area is not neutral to
> the (full IP payload) checksum because it still increases the IP Total
> Length (it changes the "pseudo-header").

Good point; that one seems to keep escaping me :-(

> >> 2. we don’t need OCS alignment; what we do need is to
> > “coordinate” the
> >
> >  alignment of a 16-bit of the length to the OCS checksum field
> >>         i.e.:
> >>         - calculate the length needed (IPlen - UDP len)
> >>         - if OCS checksum field is not 16-bit aligned to the start
> > of the
> >>           option area, then swap bytes
> >>         - add the result to the OCS checksum (‘pseudo header’
> > seems a bit
> >>           heavy here, but same point)
> >
> > I believe that is correct. Padding could still be convenient, though,
> > and I see no reason to disallow it (the current draft does permit
> > padding for alignment).
> >
>
> Would it be possible to leave this as a choice?
> CCO draft, despite on sender's side required alignemnt,
> on receiver's side only required that the complement of the sum of
> Options and pseudoheader was zero,
> in order to accept also a working CCO computed without alignment.

+1

Mike Heard