Re: [tsvwg] New Version Notification for draft-touch-tsvwg-udp-options-05.txt

[Joe Touch <[e-mail]>]

Mike,

Consider this:

if we use LITE before FRAG as you propose, then the reassembled result
has no checksum yet.

so the FRAG header could incorporate LITE if it used two different
length fields: one for the whole length, one for the checksummed length.

I.e., rather than require full "option" processing after FRAG, we could
build LITE support into FRAG itself.

Would that make sense?

Joe


On 2/28/2017 3:06 PM, C. M. Heard wrote:
> On Tue, Feb 28, 2017 at 12:03 PM, Joe Touch <[e-mail]> wrote:
>> On 2/28/2017 10:58 AM, C. M. Heard wrote:
>>> If the Fragmentation option includes its own post-reassembly checksum,
>>> then a Lite option could be inserted immediately following the UDP
>>> header in each fragment, without loss of functionality. Implementations
>>> that do not support UDP options would see UDP fragments so constructed
>>> as empty UDP datagrams and would discard them, removing the danger of
>>> accidental misinterpretation.
>> Is see how that's useful, but it would also appear to mean we might be
>> able to use LITE twice - once as this trick to hide fragments (which is
>> elegant - thanks!), but also to allow the use of LITE in the final
>> result. I'm not sure whether that makes sense yet, though - if you check
>> to see that the whole thing is there, there's little point in allowing
>> part of the packet to not be checksummed (it already would be).
>>
>> So maybe LITE couples with FRAG only in the way you mention, and no other?
> That is exactly how I would envision it.
>
> Thanks,
>
> Mike Heard