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 09:21 UTC

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To: David Farmer <>, Fred Baker <>
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From: Fernando Gont <>
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Date: Sat, 13 Feb 2021 06:19:44 -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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Hello, David,

On 13/2/21 06:00, David Farmer wrote:

> I don't think "site-local" is the right idea at all. First, let's set 
> aside ULA for a moment, and look at some other entries in the IANA IPv6 
> Special-Purpose Address Registry;
> I want to call your attention to the Local-Use IPv4/IPv6 Translation 
> Prefix (not the WKP), the Discard-Only Prefix, and the IPv6 Benchmarking 
> Prefix, they are not Globally Reachable but are Forwardable. Since they 
> are Forwardable they can't be "Link-Local Scope". But, they can't be 
> "Global Scope" either, there will most certainly be other interfaces on 
> the Internet that have the same address, and that is acceptable as they 
> are intended to be administratively limited and their uniqueness is the 
> responsibility of an administrator.

Good grief!

> So, I think we need a third scope, I propose the "Admin Scope", or the 
> "Admin-Limited Scope", but I'm open to other ideas for the name. 
> However, it can't be Site-Local, we deprecated that

"Admin-limited scope" seems fine -- and conveys the intended meaning, it 

> How do we define this third scope; this scope exists logically between 
> the Link-Local and Global Scopes, with a local administrator defining 
> the precise boundary between it and the Global Scope, including, but not 
> limited to a site boundary, with the local administrator ensuring the 
> uniqueness within the scope they define.
> Now if we agree a third scope is necessary,

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.

> then ULA most logically 
> belongs in this new third scope that is in between Link-Local and 
> Global. Yes, if the administrator randomly selects the ULA prefix as 
> defined in RFC4193, it is highly unlikely there will be an overlap, 
> however, the administrator still has the responsibility to reject any 
> overlapping randomly selected prefix to ensure uniqueness within the 
> scope that they are administratively defining.


Fernando Gont
SI6 Networks
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