Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)

David Farmer <farmer@umn.edu> Thu, 07 January 2021 11:09 UTC

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From: David Farmer <farmer@umn.edu>
Date: Thu, 7 Jan 2021 05:08:43 -0600
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To: Fernando Gont <fgont@si6networks.com>
Cc: Brian E Carpenter <brian.e.carpenter@gmail.com>, Lorenzo Colitti <lorenzo=40google.com@dmarc.ietf.org>, Mark Smith <markzzzsmith@gmail.com>, IPv6 Operations <v6ops@ietf.org>, 6MAN <6man@ietf.org>
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Subject: Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)
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Sorry for the top post.

Fernando, you are correct that by the definition of global scope in
RFC4007, ULA is not global scope.

However, Brian and RFC4139 are also correct, given the intended
reachability domain for ULA, it has a uniqueness that is many many orders
of magnitude greater than is necessary for the task. So, while not
technically global scope as defined in RFC4007 it is effectively global
scope in any way that matters.

I have an idea for what to call ULA's scope without redefining global scope
in RFC4007, how about we call ULA's scope "pseudo-global" scope.

This gives us;

Link-Local > Site-Local >>>>>> Pseudo-Global > Global

Yes, Site-Local is deprecated, it is just there for comparison. I'm trying
to show that Link-Local and Site-Local are in the same neighborhood, and
pseudo-global and global are in a completely different neighborhood.

Calling ULA pseudo-global scope I believe conveys RFC4139's original intent
without conflicting with the definition of global scope in RFC4007, while
still allowing it to be treated effectively as if it is global scope.

What do other people think?

Thanks.

On Wed, Jan 6, 2021 at 4:24 PM Fernando Gont <fgont@si6networks.com> wrote:

> On 6/1/21 18:30, Brian E Carpenter wrote:
> > Portmanteau reply to multiple messages:
> >
> > On 06-Jan-21 20:07, Lorenzo Colitti wrote: ...
> >> So I guess I'm somewhere between 1) and 3). The specs are
> >> consistent but they fail to consider human behaviour, so they don't
> >> actually work in practice.
> >
> [...]
> >
> > The problem is largely theoretical, and educational for people who
> > train IPv4 users in IPv6 terminology and practices. As Fernando has
> > pointed out, the use of the word "global" is confusing for something
> > that has L for "local" in its name.
>
> There is indeed a terminology issue, which ends up making it complicated
> to explain e.g. the concept of "scope" as a result.
>
>
>
> > On 07-Jan-21 01:17, Ted Lemon wrote: ...
> >> GUA: “valid everywhere on the internet scope” ULA: “not valid
> >> everywhere scope” LLA: “valid only on this link scope”
> >
> > Friendly amendment:
> >
> > GUA: valid everywhere ULA: Unique Limited-domain Address LLA: valid
> > only on this link
>
> Would certainly also work.
>
>
> > On 07-Jan-21 04:13, Philip Homburg wrote: ...
> >> Some things don't need fixing even if they are not 100% correct.
> >
> > +1
>
> My take is that if the topics is confusing for us, we cannot expect it
> to be any better for others.
>
>
>
> > On 07-Jan-21 05:26, Gert Doering wrote: ...
> >> Why should applications, or anything that is not an admin, care if
> >> an address is a ULA or a GUA?
> >
> > It depends on what you mean by "application". I've written code that
> > explicitly prefers a ULA, and I could imagine a security spec saying
> > "prefer ULA". But anyway, it's not really a problem, is it? (It's
> > annoying to me that in Python, a ULA has .is_global == False, but I
> > managed to code round that error.)
>
> The question is: Is it an error?
>
> I've just checked the most "up to date" textbook that I have at hand on
> IPv6. Page 335 has a subsection entitled "Global addresses versus ULAs".
> The discussion in the textbook is indeed fine.
>
> Could one actually make the case that e.g. Python's library should
> change? If it did, it would be counter intuitive. It would match
> RFC4193/4291, but not RFC4007, e.g. the textbook I've checked, and the
> intuitive meaning of private/global.
>
> FWIW, I don't think there's a problem with how ULAs work. But I do think
> that the terminology problem does have ramifications.
>
> --
> Fernando Gont
> SI6 Networks
> e-mail: fgont@si6networks.com
> PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492
>
>
>
>
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