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

Don Sturek <> Fri, 17 October 2014 19:57 UTC

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Date: Fri, 17 Oct 2014 12:56:56 -0700
From: Don Sturek <>
To: James Woodyatt <>, HOMENET Working Group <>
Message-ID: <>
Thread-Topic: [homenet] Let's make in-home ULA presence a MUST !?
References: <> <> <20141014142746.GX31092@Space.Net> <> <20141014145930.GY31092@Space.Net> <> <20141014154111.GZ31092@Space.Net> <> <20141015150422.GW31092@Space.Net> <> <20141015154841.GY31092@Space.Net> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <>
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Subject: Re: [homenet] Let's make in-home ULA presence a MUST !?
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Hi James,

One more issue that maybe needs some consideration:    How would a router
know the boundary for dissemination of ULA prefixes?  Here I am thinking of
the case where there may be more than one ISP interface and particularly in
the case of network splits and joins in the home.

So really I think there are a couple of different topics ripe for I-Ds:
1)  How to handle splits/joins of networks in the home where different ULA
prefixes are in use
2)  Guidance on when (and when not) to propagate ULA prefixes.  I think I
have heard anecdotally that most ISP see traffic using ULAs on their ISP
interface (which they drop).  It would be nice to have a definitive draft
that clearly states when this traffic should not be routed (so at least
dilligent implementers can attempt to do the right thing).  Again, I think
this topic is fairly obvious in a home with a single ISP and all devices are
connected from day 1 but it is less than clear when merging two or more
networks in your home (or attempting to split the networks)


From:  James Woodyatt <>
Date:  Friday, October 17, 2014 12:49 PM
To:  HOMENET Working Group <>
Subject:  Re: [homenet] Let's make in-home ULA presence a MUST !?

On Fri, Oct 17, 2014 at 7:17 AM, Ted Lemon <> wrote:
> On Oct 17, 2014, at 8:46 AM, Lorenzo Colitti <> wrote:
>> > Oh, ULAs and stable addressing sound good on paper, sure. But as soon as
>> you actually try to use them, then suddenly there are a boatload of scenarios
>> that you need to deal with like the ones presented by James many messages
>> ago. What happens on splits? What happens on joins? Do you need to keep old
>> ULAs around? How many? Will implementations age them out? (I can tell you the
>> answer to that one: "no"; they're more likely to stop accepting new ones than
>> to have new ones replace old ones). And so on and so forth.
> You may have missed the message where I responded to James with concrete
> proposals for how to solve these problems.   It is entirely possible that if
> we explore that solution space we will conclude, as you have, that no solution
> is reliable and not brittle, but I don't think we have explored it, so I think
> your conclusion that we will not come up with a good solution is premature.

As I recall, the proposals in your response were less than concrete and
didn't solve the problems. In particular, I remain curious about how to
expire the locally generated ULA prefixes that accumulate over repeated
network joins and splits.  I remember explaining how those events could be
rather more frequent than people might be assuming, and that's where the
discourse seemed to stop.

james woodyatt <>
Nest Labs, Communications Engineering
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