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

[Joe Touch <[e-mail]>]

+1

The current wording was, FWIW, intended to continue to allow OCS alignment if desired.

Joe

> On Mar 11, 2019, at 1:28 PM, C. M. Heard <[e-mail]> wrote:
> 
>> 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