Subject: Re: How to use properly ipv6 autoconf over a router interface?
To: None <>
From: David Young <>
List: tech-net
Date: 05/05/2006 11:52:09
On Thu, May 04, 2006 at 09:52:29PM +0000, Martijn van Buul wrote:
> It occurred to me that David Young wrote in
> > 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", 
> Maybe I *do* know more of the subject, and I'm merely a few steps ahead of
> you?
> But well then, Mr. Guru, please tell me how to address the following
> dilemma:
*snip snip*
> Really, the only way to make *any* kind of automagic routing possible would
> be address rewriting. IPv6 already autoconfigures link local addresses 
> for you, but they'd have to be rewritten to something global. In other words,
> IPv6 NAT. And you may call me names and ridicule me, but really:

You're the one calling names.  It was not my intention to ridicule you,
sorry if it came off that way.

Clearly you have thought a lot about the question.  So why didn't you
begin with your detailed and informative response (which I trimmed above)
instead of "I'm smelling IPv6 NAT here," which sounds so flippant?

Everyone has leapt to the conclusion that any IPv6 router that
autoconfigures for subnet X on one interface must necessarily advertise
subnet X on its second interface.  Suppose the IPv6 router is your
notebook computer.  The subnet on the second interface is part of a
/48 at home; your connection to home is a private tunnel.  The first
interface auto-configures for an arbitrary IPv6 subnet at work, or at
the coffeeshop, or wherever you are that day.  Your notebook forwards
packets from the second interface to the tunnel interface.  I believe
this setup is forbidden both by the current standards and by the KAME
IPv6 stack, but maybe I am mistaken.  (It looks like IETF's NEMO working
group contemplates just this kind of "mobile router" scenario.)  I am
interested to hear your opinion on the matter.


David Young             OJC Technologies      Urbana, IL * (217) 278-3933