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

Fernando Gont <> Wed, 06 January 2021 22:24 UTC

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To: Brian E Carpenter <>, Lorenzo Colitti <>, Mark Smith <>
Cc: IPv6 Operations <>, 6MAN <>
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From: Fernando Gont <>
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Date: Wed, 6 Jan 2021 19:23:49 -0300
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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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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
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