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

[Raffaele Zullo <[e-mail]>]

Hello,

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").


>> 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.

Thank you,
Raffaele Zullo