Re: [Anima] Erik Kline's Discuss on draft-ietf-anima-autonomic-control-plane-28: (with DISCUSS and COMMENT)

["Eric Vyncke (evyncke)" <[e-mail]>]

About ULA, why not simply keeping:

"    ULA: (Global ID prefix)  A "Unique Local Address" (ULA) is an IPv6
       address in the block fc00::/7, defined in [RFC4193]."

And nothing else of the existing paragraph. IMHO, there is no need to justify the choice

-éric

-----Original Message-----
From: Anima <[e-mail]> on behalf of Toerless Eckert <[e-mail]>
Date: Wednesday, 30 September 2020 at 15:55
To: Erik Kline <[e-mail]>
Cc: "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, The IESG <[e-mail]>, "[e-mail]" <[e-mail]>, Sheng Jiang <[e-mail]>
Subject: Re: [Anima] Erik Kline's Discuss on draft-ietf-anima-autonomic-control-plane-28: (with DISCUSS and COMMENT)

    Inline

    On Sun, Sep 27, 2020 at 02:52:17PM -0700, Erik Kline wrote:
    > Toerless,
    > 
    > Thanks for taking the time to go through all this.  Generally LGTM, but I
    > would like to iterate on the ULA text (nothing major).
    > 
    > 
    > > > [ section 2 ]
    > > >
    > > > * "It is the approximate IPv6 counterpart of the IPv4 private address
    > > >   ([RFC1918])."
    > > >
    > > >   I understand the intent but I don't think this statement is complete. I
    > > >   think we shouldn't let this sentence out into the wild as is since it
    > > could
    > > >   be read without any context nor even any pretense of interest in
    > > nuance.
    > > >
    > > >   May I suggest:
    > > >
    > > >   "It is often thought of as the approximate IPv6 counterpart of the IPv4
    > > >   private address space ([RFC1918]), though it is in fact meaningfully
    > > >   different in important and subtle ways [and upon which this document
    > > relies]."
    > >
    > > Thanks for not trying to talk me out of the comparison, which i
    > > successfully
    > > used to explain ULA to many customers. Your proposal is a bit too verbose
    > > for
    > > the terminoloy section, so it's now:
    > >
    > > It is often thought of as the approximate IPv6 counterpart of the IPv4
    > > private address (<xref target="RFC1918" format="default"/>). There are
    > > important differences though that are beneficial for and exploited by the
    > > ACP, such as the ULA Global ID prefix, which are the first 48-bits of a ULA
    > > address. In this document it is abbreviated as "ULA prefix".
    > >
    > 
    > It's a statement of fact that this is how people unfamiliar with this space
    > view this space.  It's apparently also a statement of fact that people are
    > still actively being told this.  ;-)
    >
    > But I still think it's not quite right.  For one, the real counterpart to
    > 1918 in IPv6 is the deprecated site-local prefix.
    >
    > Also, to say it's "often
    > thought of" in an IETF document implies more IETF folks think of this way,
    > when in reality I'm not sure that's the case.

    *cough* *cough*

    |> [ section 2 ]
    |>
    |> * "It is the approximate IPv6 counterpart of the IPv4 private address
    |>   ([RFC1918])."
    |> ...
    |> May I suggest:
    |>   "It is often thought of as the approximate IPv6 counterpart of the IPv4
    |>   private address space ([RFC1918]), though it is in fact meaningfully
    |>   different in important and subtle ways ...

    Aka: It is now your text that you would like to see revisited !

    > If you really want to leave this notion in (removing the sentence
    > altogether is good by me), perhaps we can wordsmith it a bit more.  If I
    > may propose:

    How about:

        ULA: (Global ID prefix)  A "Unique Local Address" (ULA) is an IPv6
           address in the block fc00::/7, defined in [RFC4193].  ULA is the
           IPv6 successor of the IPv4 private address space ([RFC1918]). 
           ULA have important differences over IPv4 private addresses that
           are beneficial for and exploited by the ACP, such as the Locally
           Assigned Global ID prefix, which are the first 48-bits of a ULA
           address [RFC4193 section 3.2.1].  In this document this prefix is
           abbreviated as "ULA prefix".

    Successor is hopefully more correct word. Sure, site local prefixes
    where a successor too, but i hope i do not have to write 

    "ULA is the (only surviving) IPv6 successor..."

    > OLD:
    > 
    >    ULA: (Global ID prefix)  A "Unique Local Address" (ULA) is an IPv6
    >       address in the block fc00::/7, defined in [RFC4193].  It is often
    >       thought of as the approximate IPv6 counterpart of the IPv4 private
    >       address ([RFC1918]).  There are important differences though that
    >       are beneficial for and exploited by the ACP, such as the ULA
    >       Global ID prefix, which are the first 48-bits of a ULA address.
    >       In this document it is abbreviated as "ULA prefix".
    > 
    > NEW:
    > 
    >    ULA: (Global ID prefix)  A "Unique Local Address" (ULA) is an IPv6
    >       address in the block fc00::/7, defined in [RFC4193].  Sometimes
    >       thought of as the approximate IPv6 counterpart of the IPv4 private
    >       address ([RFC1918]), there are important differences that are
    >       beneficial for and exploited by the ACP.  In this document, the
    >       "ULA prefix" refers to Locally Assigned Global ID prefixes, which
    >       are the first 48-bits of the ULA address [RFC4193 section 3.2.1].

    Beside the counterpart wordsmithing, 
    i do not like the removal of pointing out that the ULA prefix is the
    new benefit of ULA that we exploit with ACP. That was at the core of the
    explanation.

    > (I didn't think it was worth trying to get into the fc00::/8 vs fd00::/8
    > distinction in this glossary text.)

    I agree, but i do not see neither the glossary or the rest of the text
    doing that. The spec part just specifies use of fd00:/8 without
    discussion and the glossary just uses the ::/7 as thats what rfc4193 say..
    Am i missing something ?

    > > [ section 8.1.3 ]
    > > >
    > > > * Why is an RIO for ::/0 with a lifetime of 0 required?  Doesn't it
    > > suffice
    > > >   it set the default router lifetime to 0?  Separately, are all nodes
    > > required
    > > >   to be Type C?
    > >
    > > Check the new text, i hope it explains everything.
    > >
    > > Yes, type A and B do not support per-prefix auto selection of router,
    > > The lifetime of 0 is used so only Type C hosts will invalidate the
    > > default route for the ACP edge node, but not Type A/B hosts. Maybe there
    > > is another parameter combination that achieves this goal, but this was
    > > the easiest for me to assess/describe.
    > >
    > 
    > This looks better, thank you.
    > 
    > To be honest, I don't know what the point of Type A/B hosts is anymore (and
    > if it were possible to declare these anima deployments greenfield I would
    > recommend saying the default router lifetime MUST be zero in the RA header
    > to force clients to use a stack that works -- but that's just me).

    I would guess that A and B have been seen in the wild before 4191 was
    released and so the RFC was written to be inclusive. No idea.

    I have no idea how prevalent these types are, and the current described
    method may be a tiny bit more convoluted but seems to be more compatible.

    Given my deployment experience of enterprises withholding from adopting
    new network technology when it wasn't compatible with their oldest
    NMS equipment, i am a bit burned in promoting "hard cut" solutions, and
    this ben an OPS area draft instead of e.g.: RTG is a good excuse for that
    approach ;-))

    Cheers
        Toerless

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