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 16:21 UTC

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To: Ted Lemon <>
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From: Fernando Gont <>
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Date: Sat, 13 Feb 2021 13:09:43 -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 13/2/21 11:54, Ted Lemon wrote:
> On Feb 13, 2021, at 4:19 AM, Fernando Gont < 
> <>> wrote:
>> Well, whether we call it out or not, as per RFC4007:
>>              scope(LL) < scope(ULA) < scope(GUA)
>> So it's more about acknowledging facts than about introducing or 
>> needing a new scope.  The same applies to the addresses you mentioned 
>> before.
> No. scope(LL) < scope(ULA) and scope(LL) < scope(GUA) but scope(ULA) ? 
> scope(GUA). That is, any particular ULA may or may not be global in scope.

  [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"

You cannot attest that any ULA is globally unique. They are randomized, 
in a de-centralized manner, without any sort of coordination (i.e., no 
global registry).

If they were "global scope", the "topological span" would be "the 
Internet". And when you compute the birthday paradoz for *all* ULA-based 
networks in the Internet, you actually get sort of a guarantee that your 
prefix is being used elsewhere.

> The problem with admin scope is that it’s not a definitional scope, but 
> rather an operational scope.

But it still plays nicely with the above definition of scope....

> Which may be the problem—we are using the 
> term “scope” when that’s not specific enough—we could mean “by 
> definition” or “in practice” scope, but we aren’t making that clear. 

The definition of scope (and of global scope) are quite clear in 
RFC4007: "uniqueness of the address in the topological span that 
represents the scope"

Fernando Gont
SI6 Networks
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