Re: [Roll] Benjamin Kaduk's Discuss on draft-ietf-roll-turnon-rfc8138-14: (with DISCUSS and COMMENT)

Michael Richardson <mcr+ietf@sandelman.ca> Sat, 12 September 2020 17:51 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Routing Over Low power and Lossy networks <roll@ietf.org>
cc: Benjamin Kaduk <kaduk@mit.edu>, "roll-chairs\@ietf.org" <roll-chairs@ietf.org>, Ines Robles <mariainesrobles@googlemail.com>, "draft-ietf-roll-turnon-rfc8138\@ietf.org" <draft-ietf-roll-turnon-rfc8138@ietf.org>, The IESG <iesg@ietf.org>, Alvaro Retana <aretana.ietf@yahoo.com>
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Subject: Re: [Roll] Benjamin Kaduk's Discuss on draft-ietf-roll-turnon-rfc8138-14: (with DISCUSS and COMMENT)
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Pascal Thubert \(pthubert\) <pthubert=40cisco.com@dmarc.ietf.org> wrote:
    > Now I’m unsure Michael and I agree anymore.
    > What will today’s developer code?

    > We ask him to test if mop is < 7
    > What value will the developer place in his code if the test returns
    > false?

That's a good question.
Pascal, it your intention that 8138 be turned on in this case?

I'm not opposed to that conclusion, but I thought that the goal was to move
the signaling to mopex/capabilities/TBD?

Would there be cases in the future where ONLY 8138 compression would be coded?

We have set the situation where if a node does not understand the MOP, it can
be a leaf, but 8138 incompatibility makes that not work.


    > Leaving it to the implementation will have some people choose true and
    > others false. This is not what we want.

    > We want to control what the code does so we can expect it in the future
    > and build our backward compatibility based on that sure knowledge.

    > Before the draft the default was no compression. Quite naturally since
    > initially it did not exist.

    > Also we discussed on the ML that for RPLv2 all implementations MUST support the compression.

Just consider that for some link layers, 8138 compression might not make sense.

    > In which case it is a better default for a coder today to decide to use
    > the compression for mop 7, isn’t it?
    > I hope I make the case right. Just think you’re coding it!

We're assuming someone coding today.
Someone who is not writing MOP=7 code, has no mopex or capabilities code,
because we haven't defined that.
We agree that the "T" flag does not exist, and should be checked.
Such a node would be a leaf.

I can live with defaulting 8138 to be on for MOP=7 for link layers for which
8138 is appropriate. (Someone coding today will know what link layers they
have)

--
Michael Richardson <mcr+IETF@sandelman.ca>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide