1. A method for analyzing a network for abnormalities, comprising: receiving routing information from a plurality of switches within a network, the routing information including forwarding tables that list forwarding rules for forwarding packets within the network; splitting the received routing information into N portions; processing each of the N portions by identifying forwarding rules that pertain to each of M subnets belonging to the network, wherein a forwarding rule pertains to an Mth subnet if a prefix representing the Mth subnet can be fully included within a prefix associated with the forwarding rule; forming M groups of forwarding rules such that each group only includes forwarding rules that pertain to the same Mth subnet; generating M forwarding graphs for the M subnets, each of the M forwarding graphs being generated using the corresponding Mth group of forwarding rules; identifying graph properties representative of network abnormalities in any of the M forwarding graphs; and indicating network abnormalities identified in any of the M forwarding graphs, wherein M and N are integers greater than 1.