Re: [homenet] Let's make in-home ULA presence a MUST !?

James Woodyatt <> Tue, 14 October 2014 19:20 UTC

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Date: Tue, 14 Oct 2014 12:19:56 -0700
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From: James Woodyatt <>
To: HOMENET Working Group <>
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Subject: Re: [homenet] Let's make in-home ULA presence a MUST !?
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On Tue, Oct 14, 2014 at 1:24 AM, Markus Stenberg <>

> From my point of view, it should be SHOULD _always_ generate ULA (so that
> privacy oriented things in a home have a sane default without need for
> trusting firewalling), and MUST generate if no GUA around.

I don't understand [and I'm not sure I like seeing it] this clause about
"privacy oriented things" and "trusting firewalling" in the context of RFC
4193 unique local addressing. I suspect there is some conflation with RFC
1918 privacy addressing happening there [which is why I am frowning].

On the topic of the original question, if I were to editorialize here, then
I would want to see something like this:

A) An autonomously generated ULA prefix SHOULD be advertised when no other
delegated prefix is valid.

B) Whenever there is any valid delegated prefix, advertisements for an
existing autonomously generated ULA prefix MUST be deprecated, i.e. updated
with preferred lifetime of zero.

C) A deprecated autonomously generated ULA prefix MUST be withdrawn when it
expires, i.e. its valid time reaches zero.

D) Whenever there is no longer any valid delegated prefix, advertisements
for a previously deprecated autonomously generated ULA prefix MUST be
updated with non-zero preferred lifetime.

The idea here is to make sure IPv6 applications can generally rely on home
network interior routers to forward traffic among the multiple links in the
home, regardless of whether any first-mile Internet services are
provisioned, configured and operational, i.e. there shall always be at
least one preferred global scope network prefix, and there shall be an
autonomously generated local prefix available as a last resort whenever
there are no valid delegated prefixes.

james woodyatt <>
Nest Labs, Communications Engineering