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

[Joe Touch <[e-mail]>]

> On Mar 9, 2019, at 11:56 AM, Raffaele Zullo <[e-mail]> wrote:
> 
> Hi,
> 
> On 2019-03-09 19:28, Joe Touch wrote:
>>> ...
>> 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.

Yes, but there are three points to LITE:

1. less work for the transmitter (which your proposal defeats)
2. less work for the receiver (which your proposal maintains)
3. deliver potentially corrupted data (one of the original points of UDP-lite - it wasn’t just about performance)

These errant middle boxes are also thus defeating #3.

So, IMO, in the presence of those sorts of things, basically LITE with our proposal doesn’t do most of what it was intended.

Again, for that reason, I’d still prefer leaving it alone.

Joe