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

Ted Lemon <mellon@fugue.com> Fri, 17 October 2014 16:03 UTC

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From: Ted Lemon <mellon@fugue.com>
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Date: Fri, 17 Oct 2014 11:03:16 -0500
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To: Michael Richardson <mcr+ietf@sandelman.ca>
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Cc: "homenet@ietf.org" <homenet@ietf.org>, Michael Thomas <mike@mtcc.com>, "STARK, BARBARA H" <bs7652@att.com>, Lorenzo Colitti <lorenzo@google.com>
Subject: Re: [homenet] Let's make in-home ULA presence a MUST !?
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On Oct 17, 2014, at 10:54 AM, Michael Richardson <mcr+ietf@sandelman.ca> wrote:
> I will go back and read James' message about joins and splits.
> It seems that we have this problem with GUAs as well, and it seems that
> the whole address selection issue exists without ULAs, as long as one has
> multiple ISPs.

The issue with joins and splits is that you would like your numbering to survive a temporary network partition, but to not survive a permanent network partition.   I think this problem is solvable, and have some ideas about how to do it, which are half-baked and probably won't work without tweaking.

E.g., when a homenet chooses a ULA, it could divide the /64s evenly between all of the participating homenet routers.   If there's a partition, the homenet routers get to keep the /64s they got to begin with, but if after some period of time (TBD) the partition hasn't healed, one of them (chosen back when the network wasn't partitioned) begins a transition to a new randomly-chosen ULA.   If new routers are added to a homenet, HNCP should be able to balance out the pool of free /64s so that every router has some to keep during a partition.

If two homenets each with their own ULA are joined, one of the ULAs is deprecated with a long tail.   It would also be worth factoring power-cycling into this: if a homenet router that had a ULA is powered off, then powered back on, connected to a new homenet, its ULA is probably the one that should be deprecated.   This will still fail in the case that there are devices that are still using the prefix, but I think we're now down in the really unlikely scenarios that we don't have to solve.