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

Fernando Gont <> Fri, 12 February 2021 23:52 UTC

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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)
To: Ted Lemon <>
Cc: Fred Baker <>, IPv6 Operations <>, "" <>
References: <> <> <> <> <>
From: Fernando Gont <>
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Date: Fri, 12 Feb 2021 20:50:42 -0300
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Hi, Ted,

On 12/2/21 20:29, Ted Lemon wrote:
> On Feb 12, 2021, at 6:12 PM, Fernando Gont < 
> <>> wrote:
>> Both the uniqueness scope and the routing scope of ULAs are smaller than
>> that of GUAs.
> This is true, but the distinction is that there is no automatic 
> mechanism specified for knowing whether a particular ULA is in scope for 
> a link.

Well, that's because the scope of ULAs is loosely-defined. As Fred, it's 
essentially "site local", with site-local meaning whatever you want it 
to mean (or, IOW, whatever it means based on hor far such packets can be 
routed and the area where such addresses are meaningful).

> It’s perfectly valid to use the default route to forward to a 
> ULA destination. If a host were to automatically not do this, things 
> would break all over the place.

Well, but that's essentially true for anything that is not link-local -- 
because link local is the only scope that is tightly defined.

Global: Valid in all networks
Link-local: only valid within this network segement.

For the rest (e.g. ULAs), you forward them "just in case", because you 
don't really know where the scope ends.

> IOW, what Fred said is perfectly correct and sensible, but the sense in 
> which ULAs are global is that you should (MUST?) use the default route 
> to route them unless there is a more specific route that matches.

This, in away, is the question that this document somewhat raises:

* What's "global scope" anyway?

* 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. :-)

Fernando Gont
SI6 Networks
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