selective auto-aggregation

I believe we're losing the aggregation war. More and more entities are
deaggregating, and not announcing their largest aggregates which makes
prefix-length filtering less effective.

I'ld like to propose the concept of selective aggregation, whereby
a router can be configured to aggregate based upon rules.

For example, if an RIR allocation boundary for a particular /8 is
/21, that routes which are longer than /21 could be aggregated to
/21 rather than discarded. Obviously, this would only be effective
facing one's transit, since aggregating a peer would violate most
peering agreements. In transit-free networks, this functionality would
not be useful.

Similarly, the ability to auto-aggregate contiguous networks originated
by the same AS, which could be applied even to routes with lengths
shorter than an RIR boundary. This functionality could be useful
facing ones peers.

This type of thing would need to be selective, since permitted
deaggregation (no-export tagged routes with meaningful MEDs) can
still be useful between entities which agree to such things.

If we can, I'ld like to avoid a holy war on whether deaggregating
is someone's god given right, and stick to the premise that there
are networks who will enforce aggregation policies, and want to do so
in the most effective manner possible.