Subject: Re: How to use properly ipv6 autoconf over a router interface?
To: David Young <>
From: Steven M. Bellovin <>
List: tech-net
Date: 05/04/2006 15:29:59
On Thu, 4 May 2006 14:15:26 -0500, David Young <> wrote:

> On Thu, May 04, 2006 at 10:59:07AM +0000, Martijn van Buul wrote:
> > It occurred to me that David Young wrote in
> > > I can easily imagine a scenario where my Powerbook auto-configures as
> > > a host on a WiFi LAN, but it is a router for my cell and for my PDA on
> > > a Bluetooth PAN.
> > 
> > I'm smelling IPv6 NAT here.
> If people only know/think enough about the topic to speak about "smells"
> and "messiness", I don't see any reason to persist with the discussion.
That was my original reaction, but on further reflection I think it's
actually a serious question.  If you're autoconfiguring on one interface,
what prefix do you hand out to the hosts you're routing for on the other
interface?  The same one you received?  That's more like bridging.  One
you've made up?  Good luck getting it accepted globally, where CIDR rules.
A new one, available at that site?  How are you going to learn it?  I know
of no protocols for such a feature.  You're left with NATv6.

No, I don't like it, either, which is why I conclude that this isn't a
fruitful path to pursue.  Your goal is very reasonable, but I don't think
you can do it the way you've suggested.

		--Steven M. Bellovin,