Described are computer-based methods and apparatuses, including computer program products, for filtering and policing for defending against denial of service attacks on a network. A data packet is filtered by a multi-tiered filtering and transmission system. Data packets matching the first tier filter are discarded. Data packets matching the second tier filter are transmitted to an output module based on a criterion. Data packets in the third tier filter are hashed into bins and data packets matching an entry in the bin are transmitted to the output module based on a criterion for the bin. Data packets in the fourth tier transmission system are transmitted to the output module based on a criterion. Data packets that do not meet the criterion for transmission to the output module are transmitted to an attack identification module which analyzes the data packets to identify attacks.