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

[Eliot Lear <[e-mail]>]

Hi Erik

I wonder if the simpler fix is simply to replace the word “counterpart” with “analog”.

Eliot

> On 27 Sep 2020, at 23:52, Erik Kline <[e-mail]> 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.
> 
> 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:
> 
> 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].
> 
> (I didn't think it was worth trying to get into the fc00::/8 vs fd00::/8 distinction in this glossary text.)
> 
> > [ 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). 
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