Re: [Roll] Unaware-leaves - ND-Status and RPL-Status linkage

Michael Richardson <mcr+ietf@sandelman.ca> Tue, 17 December 2019 17:48 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Routing Over Low power and Lossy networks <roll@ietf.org>
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Date: Tue, 17 Dec 2019 12:48:08 -0500
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Subject: Re: [Roll] Unaware-leaves - ND-Status and RPL-Status linkage
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Pascal Thubert (pthubert) <pthubert@cisco.com> wrote:
    >> The RPL Status carrying ND Status seems not adequate,
    >> 1) RPL Status can carry only lower 6bits of the 8bits of ND Status

    > As you point out, it will be trouble if the ND status exceeds 64
    > values. Do you know any status in any RFC that does that? Can you
    > figure the case switch that tests them all with a different behavior
    > each?
    > Seems more sensible to downgrade the 6lo RC to 6 bits on the next
    > occasion.

You mean that we could change the ND status to 6-bits in the 6lo WG?
(I would have parsed ND status as being someing 6man takes care of)



    >> How about using a different ND Option in RPL messaging to keep the ND
    >> handling segregated? The unaware draft can say that this option can be carried
    >> in DCO or any other RPL message it requires. ND status/option may have to be
    >> carried only in specific cases which involves unaware leaves and as such the
    >> control overhead due to option header may not be much.
    >>

    > Now, you as much as anyone have in mind that we design for a
    > constrained space. We started with a mapping and Alvaro reacted to
    > that. So we proposed the encapsulation that you describe. And now we'd
    > have an new option? This seems really excessive when each bit
    > counts. Note that so far there is not a single RPL status defined
    > outside of those imported from ND, and each DAO-ACK is carrying 8 bits
    > of zeroes all around the world in millions of devices. We better not
    > increase the waste don't you think?

If we can map or redefine (to have a single IANA registry) things, then i
prefer that over a new option.

    >> This ND option could also be easily extended for future purposes since we may
    >> have additional fields in the future from ND to be carried with RPL.

    > RPL and ND are close family, RPL is effectively the way to support
    > non-transit links (NBMA) that the original ND did not have. RPL carries
    > ND options natively, consider PIO. I'm all for adding more options like
    > SLLAOs in DIO, as we discussed at the meeting. So I fully agree with
    > the desire/intuition.. But we do not need an ND option for that, it's
    > already meant to be this way.

It seems that we need to decide this as part of architecting the RUL, right?

--
Michael Richardson <mcr+IETF@sandelman.ca>ca>, Sandelman Software Works
 -= IPv6 IoT consulting =-