Re: ECN and fragments (was Re: [tsvwg] Mirja Kühlewind's Discuss on draft-ietf-6man-rfc2460bis-09: (with DISCUSS and COMMENT))

Suresh Krishnan <suresh.krishnan@gmail.com> Mon, 24 April 2017 03:30 UTC

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From: Suresh Krishnan <suresh.krishnan@gmail.com>
Date: Sun, 23 Apr 2017 23:30:55 -0400
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Subject: Re: ECN and fragments (was Re: [tsvwg] Mirja Kühlewind's Discuss on draft-ietf-6man-rfc2460bis-09: (with DISCUSS and COMMENT))
To: "Mirja Kuehlewind (IETF)" <ietf@kuehlewind.net>
Cc: "draft-ietf-6man-rfc2460bis@ietf.org" <draft-ietf-6man-rfc2460bis@ietf.org>, 6MAN <6man@ietf.org>, tsvwg <tsvwg@ietf.org>, "C. M. Heard" <heard@pobox.com>, Bob Hinden <bob.hinden@gmail.com>, IESG <iesg@ietf.org>, 6man-chairs@ietf.org
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On Sat, Apr 22, 2017 at 7:57 AM, Mirja Kuehlewind (IETF)
<ietf@kuehlewind.net> wrote:
> Hi Suresh,
>
> thanks this text is fine for me.
>
> I’d like propose three tiny editorial only changes/nits:
> s/Other/Further,/
> s/this basic/the basic/
> s/sufficient. e.g./sufficient, e.g./

Thanks Mirja. These edits all seem fine.

>
>      Only those headers in the Offset zero fragment packet are retained in
>      the reassembled packet. Further, fields in the IPv6 header may also
>      vary across the fragments being reassembled. Specifications that
>      use these fields may provide alternate instructions if the basic
>      mechanism of using the values from the Offset zero fragment is not
>      sufficient, e.g. Section 5.3 of [RFC3168] describes how to combine
>      the ECN bits from the different fragments to derive the ECN bits of
>      the reassembled packet.
>
> And I would be even more happier if we could add a few more words to the last sentence:
>
>      ... e.g. Section 5.3 of [RFC3168] describes how to combine
>      the ECN bits from the different fragments to derive the ECN bits of
>      the reassembled packet such that no congestion indications are lost.

This is not strictly true. If any of the fragments carries the not-ECT
codepoint, congestion indications will be lost (according to RFC3168),
but my earlier proposed text still works. So if you don't care
strongly about it, I would prefer keeping the old text.

Regards
Suresh