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

Martin Duke <martin.h.duke@gmail.com> Wed, 11 November 2020 16:27 UTC

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References: <20200911162617.GQ89563@kduck.mit.edu> <8F19C753-DCA0-4A32-BA3B-A124B2F7F745@cisco.com> <MN2PR11MB3565F2602A0DC55DE9FF3604D83F0@MN2PR11MB3565.namprd11.prod.outlook.com> <CAM4esxQBL+4wNzJTZ_+QKMCGuo4fgyxZKxr3xmFDVEAn9J7HLQ@mail.gmail.com> <E8B2CE91-7FEE-4728-A280-935B69EF3E91@cisco.com> <CAM4esxQpcWROj9mMd3iUXr1EF8kvoF8Zmq-w4BPFVW+BtDU93w@mail.gmail.com> <117497.1600481093@dooku> <MN2PR11MB356549C173D8027709AAC777D8390@MN2PR11MB3565.namprd11.prod.outlook.com> <CAMMESswOs7ZQ3502dNYBN=qJp7O9Ddi=F3UL40Ce7JGknMq-wA@mail.gmail.com> <MN2PR11MB3565C3DB9AFAABD9E8F57CF4D8330@MN2PR11MB3565.namprd11.prod.outlook.com> <20201110033438.GE39170@kduck.mit.edu> <CO1PR11MB48815ED81CFBBF1EC97A2DB2D8E90@CO1PR11MB4881.namprd11.prod.outlook.com> <CAM4esxSDPc74=eRqtAY2SffUe_eDVFD6yXVvejmOCH9-Z9eOzQ@mail.gmail.com> <CO1PR11MB4881D4F6EC013CE1338A0C04D8E80@CO1PR11MB4881.namprd11.prod.outlook.com>
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From: Martin Duke <martin.h.duke@gmail.com>
Date: Wed, 11 Nov 2020 08:26:48 -0800
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To: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
Cc: Benjamin Kaduk <kaduk@mit.edu>, Alvaro Retana <aretana.ietf@gmail.com>, The IESG <iesg@ietf.org>, "draft-ietf-roll-turnon-rfc8138@ietf.org" <draft-ietf-roll-turnon-rfc8138@ietf.org>, Routing Over Low power and Lossy networks <roll@ietf.org>, "roll-chairs@ietf.org" <roll-chairs@ietf.org>, Michael Richardson <mcr+ietf@sandelman.ca>
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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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Ah, OK, I see now that MOP7 in itself substitutes for the flag. I'm
satisfied.

On Wed, Nov 11, 2020 at 1:59 AM Pascal Thubert (pthubert) <
pthubert@cisco.com> wrote:

> Hello Martin
>
> First of all you are correct that the whole game is to recover the bits
> for RPLv2, with the idea that the features that they signaled will be
> installed and that signaling the transition will be a waste. Also RPL has
> very few of these flags available in the configuration option and the group
> insisted on getting them back after the transition.
>
> Second is to thank you for your care / the depth of your attention on that
> issue. It is indeed “touchy”. And it spans 3 drafts that are going through
> IESG in the same window of time.
>
> Let’s see below
>
> > We will eventually get there, but this will never stop being weird to
> me. :-)
>
> > Imagine 5 types of DODAG nodes:
>
> I read they support the below as opposed to the DODAG is deployed with the
> below.
>
> Type     8138? this draft? MOP5?  MOP 7?
> -------      -------   ------------    --------   ----------
>  A             N              N             N           N
> B              Y              N             N           N
> C              Y              Y             N           N
> D              Y              Y             Y            N
> E              Y              Y              Y           Y
>
> > So if IIUC, the current state of play is that B can't gracefully deploy
> into a network with A, because they have to be statically configured to
> not-compress.
>
> Or you need some management outside of RPL which is against the core
> design point that RPL should be autonomic/self-configuring
>
> > As long as B is upgraded to this draft (C), it can gracefully deploy in
> a network with A, because compression will remain off until all the A is
> gone. C and B can function together without this draft, but they won't be
> able to dynamically change compression state, FWIW
>
> Yes, that is the transition phase
>
> >  Similarly, a hypothetical D can gracefully deploy with A, as it will
> have use of these flags, but doesn't really need the flags to work with B
> or C unless you want to dynamically change state for some reason.
>
> Unclear what you mean. If the DODAG is deployed with a MOP < 5 D is a C.
> If the MOP is 5, nodes A, B, and C will have to be leaves, and the flag
> will still be off as long as there's an A in the network, else that A will
> be isolated.
>
> > Meanwhile, E will not be able to gracefully deploy with A, because it
> does not have a means to change its compression state using the DODAG
> configuration. But because of the sentence we've discussing in this thread,
> networks with C and D will have no problem because they have this text to
> help them decide whether or not to compress. They will not have the ability
> to dynamically change compression state.
>
> Same as above, if the MOP is <7, the flag still works, even if E is
> capable of some new MOPExt MOPs. If we use a MOPext (signaled by MOP=7),
> and if there are nodes of type A in the network, tose nodes of type A will
> be leaves and they'll be isolated, unless they turn into
> RPL-unaware-leaves, from which compression is not expected.
>
> > So I guess the value of the MOP 7 behavior is... to recover the bit of
> the flags? Fine, I suppose, but this would appear to have two costs:
> Yes
>
> > 1) If A is still out there when E deploys, this bit would have been
> useful, but isn't.
> It's not when E deploys, it is when the DODAG is deployed or upgraded with
> a MOP 7.
>
> > 2) I have no idea if the "dynamic change in compression state" use case
> is valuable it all, but it would certainly foreclose the possilbilty.
> We defined this flag to enable the activation of the compression in a
> brown field. Right now we have millions of nodes deployed, all of type A.
> typically utility AMI meters. Having to impose a flag day to migrate to the
> compression is not acceptable to our users. So we do not even propose it.
> and the situation is stuck. If we have a migration scenario without a flag
> day, we can ship the compression in software refreshes, and let the
> customer decide if and when to turn on.
>
> > Do I have this right?
>
> You do 😊
>
> Pascal
>
>
> On Tue, Nov 10, 2020 at 12:15 AM Pascal Thubert (pthubert) <mailto:
> pthubert@cisco.com> wrote:
> Hello Benjamin:
>
> > That said, and my apologies for a hazy memory coming back to this after a
> > couple months, in a year or N from now when mopex is finalized, how will
> > someone looking at mopex know to use RFC8138 on links where 6LoWPAN
> > Header Compression applies (and not use it otherwise)?  We are claiming
> in
> > the -14 of this document that:
> >
> >                               For a MOP value of 7, [RFC8138] MUST be
> >    used on Links where 6LoWPAN Header Compression [RFC6282] applies and
> >    MUST NOT be used otherwise.
> >
> > but I am not sure (or have forgotten) what the chain of references is
> supposed
> > to lead someone who is implementing RPL plus MOP=7 to the requirement to
> > use RFC 8138.  I don't think we should just rely on the mopex text to do
> so,
> > since we are trying to impose the requirement with this document (which
> > predates mopex by some time), and there's not anything (other than our
> > collective memories, of course) requiring mopex to remain consistent with
> > that requirement.
>
> Just to be clear for the other readers: MOPext does not exist as a
> normative reference for this work.
> The only field that exists is the MOP field in the DIO and that field is 3
> bits long, values 0..7.
>
> The normative reference that you are after is
> https://datatracker.ietf.org/doc/draft-ietf-roll-useofrplinfo/
> This is the spec that updates RPL and changes the IANA registry to
> indicate that 7 is not a MOP.
>
> There we have:
>
> "
>
> ...
>
>   Anticipating future work to revise RPL relating to how the LLN and
>    DODAG is configured, this document changes the interpretation of the
>    [dodagcfg] Registry to be limited to Mode-of-Operation (MOP)
>    specific.  The MOP is described in [RFC6550] section 6.3.1.  The
>    Options Flags Registry is renamed, and applies to MOP values zero (0)
>    to six (6) only, leaving the flags reserved for MOP value seven (7).
>
>    In addition, this document reserves MOP value 7 for future expansion.
>
> ...
>
> 11.3.  Change MOP value 7 to Reserved
>
>    This document changes the allocation status of the Mode of Operation
>    (MOP) [ianamop] from Unassigned to Reserved.  This change is in
>    support of future work related to capabilities.
> "
>
> So basically we tell the implementations from now on to test if MOP is 7,
> and in that case, the Options Flags are undefined. In other words, if MOP
> is 7, the stack must not use the option flags as if the MOP was <7. In
> fact, 7 is no more a MOP value but a reserved thingy that can be overloaded
> in the future. And yes, we intend to do just that in MOPExt.
>
> Until that happens, implementations are at a loss if they encounter when a
> MOP field that is all ones. So we need to give them instructions to cope
> with the situation. This draft derives whether to use RFC 8138 from whether
> the 6LoWPAN compression applies to the link or not.
>
> This will stay true forever, unless another RFC amends it. When/if that
> happens, the new RFC will have to consider backward compatibility with a
> legacy implementation that implements the above.
>
> Note that this line of thought applies to 3 flags, defined respectively in:
> - https://datatracker.ietf.org/doc/draft-ietf-roll-useofrplinfo/
> - https://datatracker.ietf.org/doc/draft-ietf-roll-turnon-rfc8138/
> - https://datatracker.ietf.org/doc/draft-ietf-roll-unaware-leaves/
>
> Keep safe!
>
> Pascal
>
> >
> > Thanks,
> >
> > Ben
> >
> > On Wed, Sep 30, 2020 at 04:25:10PM +0000, Pascal Thubert (pthubert)
> wrote:
> > > Hello Alvaro
> > >
> > > I uploaded both draft with the suggested update, please see
> > >
> > > https://tools.ietf.org/rfcdiff?url2=draft-ietf-roll-turnon-rfc8138-17.
> > > txt
> > > https://www.ietf.org/rfcdiff?url2=draft-ietf-roll-unaware-leaves-21.tx
> > > t
> > >
> > > Keep safe
> > >
> > > Pascal
> > >
> > > > -----Original Message-----
> > > > From: Alvaro Retana <mailto:aretana.ietf@gmail.com>
> > > > Sent: jeudi 24 septembre 2020 17:49
> > > > To: Pascal Thubert (pthubert) <mailto:pthubert@cisco.com>
> > > > Cc: Benjamin Kaduk <mailto:kaduk@mit.edu>; The IESG <mailto:
> iesg@ietf.org>gt;;
> > > > draft-ietf- mailto:roll-turnon-rfc8138@ietf.org; Martin Duke
> > > > <mailto:martin.h.duke@gmail.com>; Routing Over Low power and Lossy
> networks
> > > > <mailto:roll@ietf.org>; roll- mailto:chairs@ietf.org; Michael
> Richardson
> > > > <mailto:mcr%2Bietf@sandelman.ca>
> > > > Subject: Re: [Roll] Benjamin Kaduk's Discuss on
> > > > draft-ietf-roll-turnon-rfc8138-
> > > > 14: (with DISCUSS and COMMENT)
> > > >
> > > > On September 24, 2020 at 8:13:09 AM, Pascal Thubert wrote:
> > > >
> > > >
> > > > Pascal:
> > > >
> > > > Hi!
> > > >
> > > > > Following the meeting last Monday and subsequent the update of
> > > > > useofrplinfo by Michael (thanks Michael!) I published a new
> > > > > version of the turnon RFC
> > > > > 8138 draft.
> > > > >
> > > > > The major changes are
> > > > > - removed the formal update to RFC 6550
> > > > > - refer to useofrplinfo as the justification why the flag is not
> > > > > defined for MOP 7
> > > > > - defined the operation in MOP 7 as compression on iff the Link
> > > > > uses 6LoPWAN HC.
> > > >
> > > > Thanks for these changes.
> > > >
> > > > Because we have to cycle useofrplinfo back through (when the WG is
> > > > done with it), I asked Ben/Martin to wait for that before coming
> > > > back to this document.  It'll make it easier than tracking multiple
> > > > changes. :-)
> > > >
> > > >
> > > > OTOH, I do have comments on the recent change:
> > > >
> > > > OLD>
> > > >    Section 4.3 of [USEofRPLinfo] updates [RFC6550] to indicate that
> > > > the
> > > >    definition of the Flags applies to Mode of Operation (MOP) values
> > > >    zero (0) to six (6) only, leaving the flags reserved for MOP
> > > > value
> > > >    seven (7).  For a MOP value of 7, the bit in position 2 is
> > > > considered
> > > >    unallocated and [RFC8138] MUST be used on Links where 6LoWPAN
> > > > Header
> > > >    Compression [RFC6282] applies and MUST NOT be used otherwise.
> > > >
> > > > NEW>
> > > >
> > > >    Section 4.3 of [USEofRPLinfo] updates [RFC6550] to indicate that
> > > > the
> > > >    definition of the Flags applies to Mode of Operation (MOP) values
> > > > zero (0)
> > > >    to six (6) only.  For a MOP value of 7, [RFC8138] MUST be used on
> > > > Links
> > > >    where 6LoWPAN Header Compression [RFC6282] applies and MUST NOT
> > > > be used
> > > >    otherwise.
> > > >
> > > >
> > > > Thanks!
> > > >
> > > > Alvaro.
>