Re: [tsvwg] Comments on recent UDP options work

["C. M. Heard" <[e-mail]>]

On Sun, Nov 25, 2018 at 9:50 AM Tom Herbert wrote:
> > Do you mean LITE, or FRAG? That is definitely true of FRAG
> > without LITE (and IMHO a good reason not to use FRAG
> > without LITE).
> >
> LITE+FRAG is the obvious case that leads to ambiguity on how a
> reciever processes a packet.

OK, you are fixated on the empty datagram case. A legacy receiver sees
a sequence of empty datagrams; a receiver that implements LITE+FRAG
will see a single reassembled datagram. Agreed that it's an open
question whether the sequence of empty datagrams is harmless. If
it is not, it is necessary to ensure that LITE+FRAG is not sent without
prior negotiation or out-of-band arrangement. Oh, wait, the spec already
says to do that.

FRAG without LITE can of course create an ambiguity that is
demonstrably harmful. A legacy receiver sees a sequence of
non-empty datagrams that are acually fragments. Easy to come
up with scenarios where those apparent datagrams will be
misinterpreted. So be sure to pick on that case too; indeed,
emphasize it; but again, if the spec is followed, naked fragments
won't be sent to an unsuspecting receiver, either.

--cmh