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

Fernando Gont <fgont@si6networks.com> 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 <mellon@fugue.com>
Cc: Fred Baker <fredbaker.ietf@gmail.com>, IPv6 Operations <v6ops@ietf.org>, "6man@ietf.org" <6man@ietf.org>
References: <160989494094.6024.7402128068704112703@ietfa.amsl.com> <6fe3a45e-de65-9f88-808d-ea7e2abdcd16@si6networks.com> <F4E00812-E366-4520-AE17-7BB46E28D575@gmail.com> <b2e51a89-e8a7-9ddb-643d-63a98569b03c@si6networks.com> <CB9EA5F4-A241-46A4-A371-B2A1BFB8C72F@fugue.com>
From: Fernando Gont <fgont@si6networks.com>
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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 <fgont@si6networks.com 
> <mailto:fgont@si6networks.com>> 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. :-)

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492