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

Lorenzo Colitti <lorenzo@google.com> Thu, 16 October 2014 13:43 UTC

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From: Lorenzo Colitti <lorenzo@google.com>
Date: Thu, 16 Oct 2014 22:43:31 +0900
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To: Ted Lemon <mellon@fugue.com>
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Cc: "homenet@ietf.org" <homenet@ietf.org>, Michael Thomas <mike@mtcc.com>
Subject: Re: [homenet] Let's make in-home ULA presence a MUST !?
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On Thu, Oct 16, 2014 at 10:34 PM, Ted Lemon <mellon@fugue.com> wrote:

> >> My point was that homenets should have ULAs, and should not use GUAs
> for local communication, because GUAs can be flash renumbered,
> >>
> > Actually, they can't.
>
> Yes they can, as you just agreed:
>

No, I didn't.

You seem to define flash renumbering as "your ISP invalidates your prefix
and gives you a new one". But such an event does *not* mean that the host
can't use its previous addresses any more, because the RA sent to the hosts
cannot reduce the valid lifetime below 2 hours. So in effect that's still
graceful renumbering with a 2-hour window.

That seems to me to be begging for trouble.   As a rule routers have too
> much memory, not too little, so I find this reasoning unconvincing.
>  Taking a little memory away from the buffer cache to make the forwarding
> table bigger seems like a really good idea.
>

Routers have many different types of memories, at very different costs.
DRAM is cheap. The stuff they store forwarding tables in is not. It's
expensive and hot.


> And changing the policy table isn't that hard: if we want to have a
> special policy for the local ULA, we already have a mechanism for doing it
> that does not require O.S. vendors to hard-code a different policy table
> nor users to select one manually: stateless DHCPv6.   And for those who
> consider the use of DHCPv6 déclassé, it will still work without: you just
> won't be protected from a provider doing flash renumbering.
>

And when your ISP renumbers you, or a new ULA joins the network, you're
going to tell the hosts about the new prefix policy using what type of
packet? There's no reconfigure in stateless DHCPv6.