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

Brian E Carpenter <brian.e.carpenter@gmail.com> Sun, 14 February 2021 19:39 UTC

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To: Ted Lemon <mellon@fugue.com>, Fernando Gont <fgont@si6networks.com>
Cc: 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: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Date: Mon, 15 Feb 2021 08:39:34 +1300
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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 15-Feb-21 04:43, 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. 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.
> 
>> 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.

Exactly. The reachability of a given routeable prefix is defined *only* by the contents of the forwarding tables in a set of interconnected routers, and by definition those tables must not include any LL prefix.

At this point I'm thinking that we'd be better off not using the word "scope" at all. It's an abstraction that doesn't seem to describe anything in the real world.

   Brian