Re: draft-ietf-multi6-multihoming-requirements-06.txt

[Jay Ford <jay-ford@uiowa.edu>]

On Thu, 19 Jun 2003, Cedric de Launois wrote:
> > > A general principle would be :
> > >
> > >   IF a host receives prefix PA in a router advertisement coming from
> > >   router RA THEN choose src address PA if the host sends a packet with
> > >   RA as the first hop toward the destination (i.e. the packet is sent
> > >   through ISPA).
> > >
> > > I would insert this rule just after the 7th rule in RFC3484.
> >
> > This doesn't help in the most typical case, where there is a single router
> > advertising both prefixes. (It would only help when there are two routers
> > advertising two different prefixes to the host.)
>
> When there is a single router, source-based routing can be used. The
> router routes all packets with src address PA through ISPA.

I don't want source-based routing.  I want destination-based routing, with a
source address which works on the path I choose to that destination.  That's
the key aspect of the (srcaddr,dstaddr) selection which makes it
difficult->impossible for the host to do correctly.  It might end up being
difficult for me to do, but I want a shot at it before giving up.  (I haven't
figured out how to deal with path transitions which invalidate the chosen
(srcaddr,dstaddr) due to tight anti-spoofing filtering..., but I'm still
pondering that angle.)

> > Basically the simplest fix is using policy-based routing in your site
> > border routers.  Not typically implemented for IPv6, but should be quite
> > straightforward.
>
> Agreed. But if there are two routers, packets addressed to the wrong
> router need to be redirected in some way to the right router. The basic
> src address selection mechanism I propose just helps to avoid the
> redirection in this case. This is an heuristic that could help and that
> don't cost a lot...

That makes the srcaddr choice preempt the dstaddr choice.  I prefer it to be
the other way around.

________________________________________________________________________
Jay Ford, Network Engineering Group, Information Technology Services
University of Iowa, Iowa City, IA 52242
email: jay-ford@uiowa.edu, phone: 319-335-5555, fax: 319-335-2951