Re: dual stack & IPv6 on by default

["Fred L. Templin" <ftemplin@IPRG.nokia.com>]

I'm just dropping into this thread, and maybe this idea has already come up.
But, when the DNS returns both A and AAAA records for a destination and
when there is no v6 route, why can't the source just do automatic v6-in-v4
tunneling using an address from an AAAA record as the v6dst and an address
from an A record as the v4dst? Gives you a decision tree of sorts, i.e.:

1) when an AAAA record and a v6 route exist, use native v6. Else:
2) when both AAAA and A records exist, but no v6 route, use
     automatic v6-in-v4 tunneling. Else:
3) when an A record exists, use v4. Else:
4) destination unreachable

Fred
ftemplin@iprg.nokia.com

Erik Nordmark wrote:

> > That's a really good question.  I'm not sure what would be the best way
> > to address this.  What we're saying in this draft is that operational
> > experience has shown that this part of ND could be problematic in some
> > circumstances.  Does ND need to be changed as a result?  Probably not.
> > There are no MUST's surrounding that bit of ND.  As implementors, we're
> > free to interpret the spec in a sane mannor.  With this draft, we're
> > pointing out reasons why implementors may want to be careful with that
> > part of ND.  There is informational value in this alone without having
> > to muck with the ND spec itself.
> >    
> A possible way to approach this problem would be to make
> the choice between A and AAAA be a function of whether there
> is one or more IPv6 route off-link (or at least one IPv6 router sending RAs).
>
> That way you don't have to tweak ND. But you do end up with some
> having e.g. getaddrinfo() check with the kernel. I think getaddrinfo()
> needs to already do some checks in order to implement the default address
> selection document.
>
>  
> > 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?
> >    
> If you have two nodes communicating on a link and the router
> dies for long enough time it seems useful to be able to
> continue to communicate. Of course, the communication will fail
> once the addresses become invalid but that might take a long time.
>
>  Erik
>
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