1) Provider X can announce the aggregate outside of the area & thus
give free transit to the whole area; or2) Provider X can announce just provider X's customers outside of the
area, thus defeating the gain from aggregation; or3) Provider X can be paid by everyone else in the area to provide
transit to the entire area to where ever else Provider X connects to.
Just to be vicious, I think I should mention option #4:
Provider X can announce the aggregate outside of the area and
drop packets bound for people in the area who do not pay
Provider X for transiting packets to them.
I think you will find that if a system were set up such that
there were many touchdowns of this nature (announcing a
single prefix), people would be screaming that they were at
the mercies of the decisions about to whom in each local
aggregate each long-distance carrier would be willing to
deliver traffic.
One could also view this as a way to push the problems of
CIDRization out to the edges -- it would then be the end
sites which would have to learn and be able to route towards
the exceptions in the local aggregates, rather than the
long-haul carriers.
Sean.