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

[Raffaele Zullo <[e-mail]>]

Hi,

On 2019-03-09 19:28, Joe Touch wrote:
> 5. the LITE only case
> 
> The whole point of LITE is that some of the IP payload isn’t 
> checksummed.
> 
>> Given that we're supposed to veryify such receivers can accept
>> LITE (w/o FRAG) and hold soft state, maybe this is acceptable?
> 
> 
> We don’t have a requirement that such receivers can accept LITE before
> we start using it, so soft state won’t help here.
> 
>> we can send
>> LITE (w/o FRAG) using UDP checksum of zero, and the additional
>> option encoding the actual checksum for the UDP data.
>> 
>> This additional checksum could simply be the existing defined
>> ACS option.
> 
> ACS uses a CRC, not IP checksum. That’s a LOT more work in software,
> so this isn’t a viable alternative.
> 
> IMO, we leave this one alone. The whole point of LITE is to do less
> work - if that means the LITE data corrupts the entire packet, then so
> be it. Then LITE basically fails.
> 
> ------

The case of LITE or more generally when checksum should not cover the 
full Options area
could be partially solved with a CCO of 4 bytes
(the original CCO proposal had a variable length for further 
flexibility).

the first 2 bytes contains the checksum of UDP Options you want to 
cover,
the other 2 bytes contains the additional compensation value for the 
uncovered bytes, for the traversal only.

The receiver can still validate the covered Options without the effort 
of summing the unnecessary Option bytes (e.g. LITE DATA),
and without risking to drop a packet for an error on the uncovered 
bytes.

Anyway the sender will still need to sum the uncovered bytes.

Thank you,
Raffaele Zullo