1. A method for determining network nodes for aggregating addresses in routing information used for routing data packets over a network, comprising the steps of: receiving link data that indicates direct links between each router in a plurality of candidate routers of a network and at least one of a different router in the network and a network segment in the network; receiving reachability data that indicates a set of one or more contiguous network addresses that can be reached on each link described in the link data; determining a measure of possible aggregation of contiguous network addresses at the plurality of candidate routers based on the link data and the reachability data; and determining a preferred router among the plurality of candidate routers to aggregate addresses in routing information sent between routers in the network based on the measure of possible aggregation at each router in the plurality of candidate routers.