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

Fernando Gont <> Sat, 13 February 2021 00:29 UTC

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From: Fernando Gont <>
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Date: Fri, 12 Feb 2021 21:29:17 -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 21:04, Ted Lemon wrote:
> On Feb 12, 2021, at 6:50 PM, Fernando Gont < 
> <>> 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.”

That's certainly not the definition of "global" we currently have.

(draft-gont-6man-ipv6-ula-scope points to the relevant places)

Me, I wouldn't use the "default route" in the definition of "global". 
 From a routing pov the default route is simply yet another route, 
albeit with a zero-len mask.

Addresses need to be able to identify the intended sender/recipient. So 
the area where they can do that limit their scope.

Now, if I use fd00:1234:5678:abcd::/64 on my net, and you use the same 
prefix on yours, and both usages are legitimate, then that's an 
indication that the scope of ULAs cannot be global.

>> * 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.

Please define "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.”

This is the definition of "scope" and "global scope" from RFC4007:

    [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"

ULAs can certainly NOT be used in the Internet-wide span, and they 
certainly do not "uniquely identify interfaces anywhere in the Internet".

> 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.

Fernando Gont
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