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> Sun, 14 February 2021 20:28 UTC

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To: Ted Lemon <mellon@fugue.com>
Cc: Brian E Carpenter <brian.e.carpenter@gmail.com>, David Farmer <farmer@umn.edu>, Fred Baker <fredbaker.ietf@gmail.com>, IPv6 Operations <v6ops@ietf.org>, "6man@ietf.org" <6man@ietf.org>
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From: Fernando Gont <fgont@si6networks.com>
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Date: Sun, 14 Feb 2021 17:27:45 -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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Hi, Ted,

On 14/2/21 12:43, Ted Lemon wrote:
> On Feb 14, 2021, at 1:00 AM, Fernando Gont <fgont@si6networks.com 
> <mailto:fgont@si6networks.com>> wrote:
>> IMO, if the areas overlap, the scope ofa ULA1 and ULA2 are still the 
>> same. One scope is Area(ULA1): all the area where ULA1 addresses are 
>> unique and can be actively employed. The other one is Area(ULA2).
>>
>> The intersection of the two areas is part of the scope of each of the 
>> two ULAs (because in that region both ULA1 and ULA2 are unambiguous)
> 
> Since you still haven’t clearly articulated what you mean by “scope” 
> with respect to ULA, it doesn’t make sense to say that one ULA has the 
> same or a different scope than another.

Scope is "scope" as defined in RFC4007:

       "[the] topological span within which the address may be used as a
       unique identifier for an interface or set of interfaces"


For ULA, that means the site or organization that you have 
administrative control (since that's the only way in which you can 
guaranteed ULAs to be unambiguous)




> In any case, what you are 
> describing here is precisely what the “label” entry in an RFC 6724 
> policy table does. Which is to say, you are not talking about scopes.

How could you possibly an inconsistency in RFC4194 and RFC4007 with a 
"source address selection" document?



>> This is not that different from the overlap of e.g. link-locals and 
>> GUAs on a local link….
> 
> Since the different treatment of GUAs and LLAs on a link is something 
> that can be known by definition, and thus be handled by if-then-else 
> statements rather than by table lookups, I would say that they are quite 
> different.

The fact that things "work" in practice doesn't imply rhar the 
architecture or it's definitions are correct.

Again, this discussion boils down to:

    [RFC4007] defines the scope of an address as:

       "[the] topological span within which the address may be used as a
       unique identifier for an interface or set of interfaces"

    And defines the "global scope" to be used for:

       "uniquely identifying interfaces anywhere in the Internet"


But ULAs, and several other prefixes raised by David ar considered 
"global scope" by RFC4291. Isn't the inconsistency clear?

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