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

Derek Fawcus <dfawcus+lists-tsvwg@employees.org> Tue, 28 February 2017 21:46 UTC

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Date: Tue, 28 Feb 2017 21:46:48 +0000
From: Derek Fawcus <dfawcus+lists-tsvwg@employees.org>
To: Joe Touch <touch@isi.edu>
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Subject: Re: [tsvwg] Fwd: New Version Notification for draft-touch-tsvwg-udp-options-05.txt
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On Tue, Feb 28, 2017 at 01:17:16p.m. -0800, Joe Touch wrote:
> Hi, Tom,
> 
> OK - so I think you and Derek are basically arguing for an Internet
> checksum to verify reassembly, rather than using a new or stronger one.

Actually,  I made a mistake.  I attributed to Tom what was I believe
was actually suggested by C. M. Heard - namely the suggestion to
combine FRAG+LITE as a way of allowing existing hosts to discard fragments.

In that he was suggesting adding an overall reassembled checksum,
which would be necessary as otherwise the repurposed reassembled
Lite payloads would not have a checksum.  I was simply pointing
out that in that scenario,  the same could be achieved with a
single CHECKSUM option, carried in only one of the FRAG packets.

So there would be no need to change the FRAG header definiton to
add a checksum there.

In the normal case of reassembling FRAG'ed payloads,  I don't see
that an overall checksum gains us anything.

Possibly an overall CRC would have some value?  That would seem to
require a second type of ACS-like option, i.e REASSEMBLE-ACS?
Again it would only need to be sent with only one of the FRAG
containing packets.  Is such an addition worth it?

DF

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