Re: dual stack & IPv6 on by default

[Erik Nordmark <Erik.Nordmark@Sun.COM>]

> 
> If you don't have a route to the destination, why try to reach it
> on-link just in case the destination might happen to be on-link?  Is
> there a situation where this would be useful?
> 

Back when the ND spec was written the idea was that if two nodes can
communicate on a link (e.g. using global addresses) it would be nice if they
could continue to communicate even if the router(s) to the link disappear.

I don't recall if there were any assumptions about the relative lifetime
of the addresses they are configured (using stateless, dhcp, or manual)
and the on-link prefixes advertised by the routers.
But given that the ND spec allows a configuration where the routers
don't advertise on-link prefixes (which causes initial packets to go through
the router and then be redirected to the on-link destination)
it would seem useful to be able to communicate after the router has
gone away.

  Erik