Re: [mif] Some thoughts

[William Herrin <bill at herrin.us>]

On Wed, Nov 18, 2009 at 4:31 AM, Scott Brim <Scott.Brim at gmail.com> wrote:
> Bill, I don't understand exactly what you're saying but it seems to
> be something like:
>
>  - An endpoint may have multiple addresses assigned to it on a single
>    interface.  It could even have addresses from different PA
>    prefixes from upstream providers.
>  - If source address and upstream provider path don't match, packets
>    could be dropped.
>  - Address selection itself can't help here, so you suggest that
>    routing take source address into account until packets get beyond
>    where uRPF is enforced.

Hi Scott,

That too, but I'm trying to convey what I think is a more important
notion: Address selection is classically a simple function on the
routing table: pick the primary address of the interface the
destination routes out of. With multiple administrative domains,
address selection may *still* be a simple function on the routing
table... the more significant difference may be in the routing table
itself.

That notion is suggested by the following example:

(A,B,C)-D-(E,F)

Where A, B, C are hosts, D is a router and E, F are ISPs supplying two
different administrative domains with unique blocks of PA addresses.
The two domains propogate from E and F down through D to hosts A, B
and C. A, B, C and D *all* need to do the right thing with respect to
source address selection and route selection based on source address.
*AND* if D is a complex network instead of a simple router, that
complex network needs a *dynamic routing protocol* that helps the
routers in D do the right thing, not just static policy routing.

I'm not sure if MIF is correctly scoped for that, but offer the
thought that maybe it should be.

Regards,
Bill Herrin


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