RE: Alternatives to source address rewriting (was RE: Preserving established communications (was RE: about draft-nordmark-multi6-noid-00)

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

> I actually currently trying to understand what will all be needed
> to provide
> flexible source address based routing. For instance,
>  - is there an impact on routing protocols needing to carry additional
>    information?

Source address based routing needs as many routes as different prefixes it
has configured, ok?
For example, if a site is dual homed and it has two different prefixes, then
the source address based routing system requires two routes.
Moreover, these routes have to point to the site exit router corresponding
to the ISP that has delegated the prefix.
This don't need to be dynamic, since the isp that delegated the prefix
doesn't change
So i guess that there is no need for special routing protocols to support
source address based routing

>  - is there an assumption about who wins when the sender has specified
>    a source address but the routing system knows that sending packets
>    out that ISP doesn't work? is less likely to work than sending it
>    out some other ISP?
>

I guess this is what we were discussing when we were considreing the rewrite
ok bit.
I think that the host should be able to decide if the packet will be routed
according the destiantion address (in which case rewriting is probably
needed to deal with ingress filtering) or it will be routed based on the
source address (in which case no rewriting occurs)
I see source address based routing as a mechanism to let the host source
address selection act as ISP selection mechanism that overrules the isp
selection performed by the routing system.
The host then would force the ISP selection in cases when it knows better
(ULP hints) or when it knowns it can't use source address rewriting (the
other end in not M6 enabled)
Regards, marcelo

> Once I understand it a bit more maybe I can answer your question whether
> we need different approaches for different types of sites.
>
>   Erik
>
>