Re: [Tsv-art] [Last-Call] [lp-wan] Tsvart last call review of draft-ietf-lpwan-coap-static-context-hc-12

Joseph Touch <touch@strayalpha.com> Wed, 18 March 2020 14:56 UTC

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From: Joseph Touch <touch@strayalpha.com>
In-Reply-To: <27E35DC7-C83E-4C6C-984A-3AC1C183BC28@kuehlewind.net>
Date: Wed, 18 Mar 2020 07:55:56 -0700
Cc: "<dominique.barthel@orange.com>" <dominique.barthel@orange.com>, "draft-ietf-lpwan-coap-static-context-hc.all@ietf.org" <draft-ietf-lpwan-coap-static-context-hc.all@ietf.org>, "last-call@ietf.org" <last-call@ietf.org>, The IESG <iesg@ietf.org>, "lp-wan@ietf.org" <lp-wan@ietf.org>, "tsv-art@ietf.org" <tsv-art@ietf.org>, "draft-ietf-lpwan-ipv6-static-context-hc@ietf.org" <draft-ietf-lpwan-ipv6-static-context-hc@ietf.org>, Benjamin Kaduk <kaduk@mit.edu>
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To: Mirja Kuehlewind <ietf@kuehlewind.net>
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Subject: Re: [Tsv-art] [Last-Call] [lp-wan] Tsvart last call review of draft-ietf-lpwan-coap-static-context-hc-12
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> On Mar 18, 2020, at 5:50 AM, Mirja Kuehlewind <ietf@kuehlewind.net> wrote:
> 
>> Indeed, the protocol parser and the SCHC rules need to know about the UDP
>> TLVs if one wants to compress them.
>> But the same is true of all the other fields. I don't think this one
>> warrants a special notice.
>> What I insist on is that, if an implementation does not know of the UDP
>> TLVs, it will not reconstruct an erroneous UDP Length, even for a packet
>> that contains these TLVs, assuming that the protocol parser checks the UDP
>> and IPv6 lengths for consistency.
> 
> I think this last statement (“protocol parser checks the UDP
> and IPv6 lengths for consistency”) is the important point that needs to be explicitly mention in the document!

That way of phrasing it is dangerous - it implies that when the values differ there is some sort of error.

It would be more in line with current TSV efforts to standardize UDP options to say “UDP length can be compressed when it *can* be computed from the IP length” and that “it MUST NOT be compressed as computable otherwise”.

Joe