Why not calculate all the routes in one place? These days when "next
hop shortest path / reachability" style routing is no longer correct,
we need to have a central place to apply policy. The interesting
thing about policy is that is has little to no place for dynamic
rerouting. Policy is a force for rigidity.
It sure seems like the people working on tag switching are more
interested in keeping their low-capacity switches and routers alive a
little longer than in implementing policy. What the world needs is
policy because policy equals differentiated billing rates. This looks
like a train to me.