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

Mark Smith <> Thu, 07 January 2021 21:23 UTC

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From: Mark Smith <>
Date: Fri, 8 Jan 2021 08:22:38 +1100
Message-ID: <>
To: Brian E Carpenter <>
Cc: Philip Homburg <>, 6man WG <>, IPv6 Operations <>, David Farmer <>
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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 Brian,

On Fri, 8 Jan 2021, 07:32 Brian E Carpenter, <>

> On 08-Jan-21 00:52, Philip Homburg wrote:
> >> I have an idea for what to call ULA's scope without redefining global
> scope
> >> in RFC4007, how about we call ULA's scope "pseudo-global" scope.
> >
> >> What do other people think?
> >
> > In my opinion we need to kill the RFC 4007 scope concept.
> >
> > We can define for example 'address types' that have no scope, but as a
> way
> > to label different types of addresses.
> This.
> Link-local needs an interface ID or interface index, which is meaningless
> outside the host.

While I do agree that interface ID is much more closer to the truth, it
seems that one reason for zone rather than interface ID for link-locals in
RFC 4007 was to inform a multi-interface node that it had multiple
interfaces attached to the same link, informing it that the corresponding
interface link-local addresses are attached to the same link.

I don't know what the use case for that is or was expected to be (layer 3
inbound/outbound load balancing or redundancy?), however it sounds like it
would be useful for a host to continue to have the knowledge. It would be
lost with pure IPv6 interface enabled IDs. I don't think shared GUA/ULA
prefixes across interfaces could be entirely relied on to determine that,
as it is theoretically possible for multiple interfaces on the same host
attached to the same link to have different GUA and/or ULA prefixes
(perhaps by manual configuration because the received RAs don't PIOs with
the A bit enabled, or any PIOs).

Perhaps preserve the idea of a zone, that in most but not all cases would
also be the same as interface ID, but only for the link-local unicast
prefix (and for all scopes of multicast addresses).


> All other unicast addresses are routeable, and do not require an
> associated interface ID. The range of reachability is always
> administratively defined, with default behaviours (ULA = limited domain
> reachability, GUA = global reachability).
> We could have a greatly simplified RFC4007bis in that case.
>     Brian
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> v6ops mailing list