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 20:19 UTC

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To: Ted Lemon <>, David Farmer <>
Cc: Fred Baker <>, IPv6 Operations <>, "" <>
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From: Fernando Gont <>
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Date: Sat, 13 Feb 2021 17:15:41 -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 13/2/21 16:32, Ted Lemon wrote:
> On Feb 13, 2021, at 2:25 PM, David Farmer < 
> <>> wrote:
>> Wait a minute! It doesn't say SOME addresses in the global scope are 
>> globally unique, it says ALL addresses in the global scope are 
>> globally unique. Unless each and every ULA address is globally unique, 
>> then ULA can't be global scope.
> The problem with things like “admin scope” is that it doesn’t help me. 
> Suppose an address is “admin scope.” Okay, how does my behavior change? 
> Can you clearly state a rule that describes what my behavior should be?

RFC6724 (Source Addr Selection).

It has a rule based on address scopes.

(Unfortunately, the rule for ULAs needs to be conveyed via a prefix, 
because of the current definition of the ULA scope).

> So what I think “global scope” means is “there isn’t some context in 
> which, by definition, this address is invalid.”

Well, other addresses also share the same property -- they are valid, 
but they identify a different thing -- an interface in a different 
subnet.  e.g., address fe80::1 is valid on avery single network segment 
-- but the issue is that, en each of them, it most likely identifies a 
different thing. -- and that comes from the uniqueness property.

So you can think of global scope as implying "being globally unique", or 
as "the address identifies the same thing, regardless of where the 
address is processed".

Fernando Gont
SI6 Networks
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492