Tension: Scalability versus QoS
Scalability calls for aggregating flows into precedence classes
Also, aggregating destinations results in fewer routing entries, but less granularity of routing decisions
Performing disaggregation gives finer granularity at a higher cost
E.g. more detailed routing advertisments can allow more granular choice of paths that better satisfy QoS requirements
OSPF can advertise multiple costs per link, and compute multiple shortest paths
Or, loose source route through a particular service provider, or multiple addresses/names per host