RE: dual stack & IPv6 on by default

[Mika Liljeberg <mika.liljeberg@welho.com>]

On Mon, 2003-03-10 at 04:04, Bound, Jim wrote:
> Good point.  But isn't it up to the implementation for links that had to
> deal with on-demand.  As long as I have route for a link then I should
> apply it? The problem would be if the link information was not applied
> before the on-demand was accessed in a multi-home manner.  But then I
> would assume destination unreachable would be the response to the
> application, though it should say link not known IMO.  So isn't the
> multi-home scenario a two step problem.  1) the on-demand NIC has to see
> the link before used by the app, and 2) the implementation must be able
> to propogate attributes for multiple interfaces?

The question also is: what triggers the on-demand link setup? Two
potential cases:

a) there is an on-link default route to the on-demand interface -> first
packet routed to the interface starts link setup

b) on-demand link setup starts on no-route, according to preset policy

Suppose we have a wireless terminal with two interfaces: a dialup one
(e.g. cellular circuit switched data) for Internet connectivity [DOWN],
and 802.11 for ad-hoc or cheap Internet access via an access point [UP].

If one takes the ND spec strictly, case a) might or might not trigger
dialup, depending on which default route we hit first. Case b) would
never trigger the dialup [although an implementation might choose to do
so after NUD].

On the other hand, as soon as the host receives the first RA from the
dialup interface and configures a default router, the other interface
stops working for ad-hoc.

All this just goes to show that the default on-link route implied by the
ND specification perhaps isn't fully thought out, at least with
multihoming. Besides, such a route could always be configured explicitly
if the user wants to use a particular interface for ad-hoc.

[I'm not sure if this actually has any additional implications to the
dual stack issue raised by the original poster.]

	MikaL