RE: Preserving established communications (was RE: about draft-nordmark-multi6-noid-00)

["marcelo bagnulo" <mbagnulo@ing.uc3m.es>]

> > But we don't have to go this far. We know that if a source address tied
> > to ISP A is used, there is no use in forwarding the packet to ISP B,
> > and the other way around. So there is no need to even check whether the
> > destination is even reachable through the ISP indicated by the source
> > address as there is no alternative course of action to forwarding the
> > packet to that ISP and hope for the best. So essentially we're just
> > taking default routes.
>
> But to solve Macelo's example where packets to destination PC:X and PD:X
> both exit Y's site over the same link/ISP (and it takes a long time to
> discover that that link/ISP has failed), you would actually
> need something stronger. For instance something along the lines
> of being able to configure the routers so
> that packets with the source prefix PA
> all-other-things-being-equal(?) exit
> via ISP A and source prefix PB exit via ISP B. That
> way the sender can explore the two ISPs by changing the source locator.

IMHO You would want to use the source address based routing when you don't
want to use source address rewriting.
There are some situations where you don't want the rewrite to take place and
you want source address based routing. I can think of the following:
- The external host don't support M6
- The M6 context has not been established yet
- An ULP hint made the M6 layer to select a different path, so you want to
let the host select the ISP and not the routing system

Note that source address routing means that the host selects the exit ISP
and source address rewriting means that the routing system selects the exit
ISP.

So a possible approach would be that if the rewrite ok bit is set, then you
perform destination address routing and if the rewrite ok bit is not set you
do source address based routing.
Does this makes sense?

Regards, marcelo

>
>   Erik
>
>