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

Ted Lemon <mellon@fugue.com> Sat, 13 February 2021 00:04 UTC

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From: Ted Lemon <mellon@fugue.com>
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Date: Fri, 12 Feb 2021 19:04:09 -0500
In-Reply-To: <dff93a2e-f4f8-01c9-ce88-c2dbb20a04f1@si6networks.com>
Cc: Fred Baker <fredbaker.ietf@gmail.com>, IPv6 Operations <v6ops@ietf.org>, "6man@ietf.org" <6man@ietf.org>
To: Fernando Gont <fgont@si6networks.com>
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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 Feb 12, 2021, at 6:50 PM, Fernando Gont <fgont@si6networks.com> wrote:
> This, in away, is the question that this document somewhat raises:
> 
> * What's "global scope" anyway?

Global scope is “you can forward it to the default route.”

> * And, given what we have right now, either the definition of scope is flawed (as in the scoped addressing architecture), or ULAs are not global, or both. :-)

RFC 4007 has a concept of “interfaces belonging to a zone,” and has a nice diagram with several organizations that we might say is a non-overlapping Venn diagram. But ULAs don’t have to have a non-overlapping Venn diagram. So they are global. And indeed there is no way to automatically determine (without configuration) which zone any given address belongs to. So in effect the only two scopes that can be automatically determined are “link local” and “global.” There can be no other scope, in the sense of a scope that can be automatically determined.

This doesn’t mean that RFC 4007 is useless, but what it does mean is that when we assign a scope to “ULA,” the only scope that makes sense is “global.”

So maybe a better question to ask is, why are we discussing this? What problem are we trying to solve?