It used to be that if something was in the routing table, it was
reachable. Today, if there is an aggregate in the routing table, the
aggregated (sub)networks had better be reachable. If we do
locator/identifer seperation, being reachable is still a good idea but
if a set of locators isn't: too bad. We don't flood this information
throughout the network and we also don't have to repair it using
backdoor routes or tunnels. So routing becomes much less dynamic.
I am not really following this. There is not functional difference
between having an aggregate route point to a "IGP more specific view"
and generate a no route to host or if the route is missing from the DFZ
and then generating a no route to host.