Re: [dtn] [EXTERNAL] Benjamin Kaduk's Discuss on draft-ietf-dtn-bpbis-22: (with DISCUSS and COMMENT)

"Burleigh, Scott C (US 312B)" <scott.c.burleigh@jpl.nasa.gov> Mon, 10 February 2020 20:51 UTC

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From: "Burleigh, Scott C (US 312B)" <scott.c.burleigh@jpl.nasa.gov>
To: Benjamin Kaduk <kaduk@mit.edu>, The IESG <iesg@ietf.org>
CC: "draft-ietf-dtn-bpbis@ietf.org" <draft-ietf-dtn-bpbis@ietf.org>, "Fred Templin" <fred.l.templin@boeing.com>, "dtn-chairs@ietf.org" <dtn-chairs@ietf.org>, "dtn@ietf.org" <dtn@ietf.org>
Thread-Topic: [EXTERNAL] Benjamin Kaduk's Discuss on draft-ietf-dtn-bpbis-22: (with DISCUSS and COMMENT)
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Date: Mon, 10 Feb 2020 20:51:23 +0000
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Subject: Re: [dtn] [EXTERNAL] Benjamin Kaduk's Discuss on draft-ietf-dtn-bpbis-22: (with DISCUSS and COMMENT)
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Ben, I gave you the wrong answer on this one:

...

Why is the last-received fragment special that it's payload is replaced by the entire payload?  Wouldn't it make more sense to promote the fragment with offset zero, since that is guaranteed to have the right extension blocks?

	Because those other fragments might have been discarded; all we need to retain is their payloads.  The extension blocks that need to be "right" should have been replicated in all fragments.
...

*** 	No, those other fragmentary bundles should NOT have been discarded: they all still have the "Reassembly pending" retention constraint, so until that constraint is removed (or their lifetimes expire) they should still be in the system.
	I think it is still the case that placing the reassembled payload in the last-received fragment should work because all important extension blocks from the original bundle should have been replicated in all fragments.
	But mistakes happen.  It would be safer to replace the payload of the offset-zero fragment with the reassembled payload and then process that bundle rather than the last-received fragment.  I'll tweak 5.7 and 5.9 to require this.

Scott