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> Sat, 13 February 2021 22:25 UTC

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To: Fernando Gont <fgont@si6networks.com>, David Farmer <farmer@umn.edu>, Fred Baker <fredbaker.ietf@gmail.com>
Cc: 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: Sun, 14 Feb 2021 11:25:44 +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 14-Feb-21 10:33, Fernando Gont wrote:
> On 13/2/21 18:17, Brian E Carpenter wrote:
>> On 13-Feb-21 22:19, Fernando Gont wrote:
>> ...
>>> Well, whether we call it out or not, as per RFC4007:
>>>
>>>                 scope(LL) < scope(ULA) < scope(GUA)
>>
>> And there's the fallacy. This inequality only makes sense if reachability is strictly a matter of concentric circles. It isn't. Nice math, but not reality.
>>
>> Slide 4 of https://www.cs.auckland.ac.nz/~brian/scope6.pdf
> 
> I don't follow. In all of your slides Area(link-local) < Area(ULA) < 
> Area(global)....

I probably need to add the case that isn't shown, i.e. "GUA" prefixes *not* being routed Internet-wide, at which point the scope difference between a ULA prefix and a "GUA" prefix sort of vanishes. Area(global) isn't really a thing, just as the BGP4 default-free zone isn't really a thing. And when Area(ULA1) overlaps with Area(ULA2) you suddenly have another scope that is Area(ULA1+ULA2). 

So guess what I'm trying to say is the inequality isn't the least bit useful.

    Brian
> 
>