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

Fernando Gont <fgont@si6networks.com> Sat, 13 February 2021 03:18 UTC

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To: Ted Lemon <mellon@fugue.com>, Fernando Gont <fernando@gont.com.ar>
Cc: v6ops@ietf.org
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From: Fernando Gont <fgont@si6networks.com>
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Date: Sat, 13 Feb 2021 00:13:00 -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 12/2/21 21:53, Ted Lemon wrote:
> On Feb 12, 2021, at 7:29 PM, Fernando Gont <fernando@gont.com.ar 
> <mailto:fernando@gont.com.ar>> wrote:
>>> So maybe a better question to ask is, why are we discussing this? 
>>> What problem are we trying to solve?
>>
>> As per the above, either the definition in the scoped addressing 
>> architecture is wrong, or flagging ULAs as "global scope" is incorrect.
>>
>> The problem I'm trying to solve is one of architecture, so to speak.
> 
> RFC 4007 only defines two scopes for unicast addresses: “link local” and 
> “global.” In this taxonomy, ULA is clearly and unambiguously global, so 
> there is no mistake.

Global scope, as per RFC4007:

       "uniquely identifying interfaces anywhere in the Internet"

Of course, ULAs don't "uniquely identify interfaces anywhere in the 
Internet".

(you only have a low-probability of collisions if/when a limited number 
of ULA-based networks are interconnected -- but that's quite different 
from the above definition)




> But you think there’s a problem. In order for us to know what to do 
> about this problem, you need to be able to articulate it in a way that 
> makes sense to us. The best way to do so is to point to a case where the 
> behavior of some system will be incorrect because this was not specified 
> correctly. Can you point to such a case?

The problem is in the scoped addressing architecture and the definition 
of "scopes" vs. the definition of ULAs.

Since it's a problem with the architecture you probably won't see a 
direct problem arising from it.

You might argue that architecture is not important (I'd disagree with 
that :-) ), but, at the end of the day, if it's not important, why 
pretend to have one in the first place? (in particular when there's no 
consistency with the actual protocols)


As noted, the only practical implications I've seen have been:

* Folks willing to have a registry for ULAs, on the expectations that
   they are indeed unique -- whcih they are not!

* Folks having a hard time understanding the addressing architecture --
   in particular the scoped addressing architecture (RFC4007) and how
   that applies to actual specs (e.g., definition of ULAs)


Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492