A method and apparatus are presented for determining network nodes for aggregating addresses in routing information used for routing data packets over a network. Link data and reachability data are received. Link data indicates direct links between each of multiple candidate routers of a network and a different router or a network segment. Reachability data indicates a set of one or more contiguous network addresses that can be reached on each link described in the link data. A measure of possible aggregation of contiguous network addresses is determined at the candidate routers based on the link data and the reachability data. A preferred router to aggregate addresses in routing information sent between routers in the network is determined among the candidate routers based on the measure of possible aggregation at each candidate router.