A packet processor provides for rule matching of packets in a network architecture. The packet processor includes a lookup cluster complex having a number of lookup engines and respective on-chip memory units. The on-chip memory stores rules for matching against packet data. A lookup front-end receives lookup requests from a host, and processes these lookup requests to generate key requests for forwarding to the lookup engines. Based on information in the packet, the lookup front-end can optimize start times for sending key requests as a continuous stream with minimal delay. As a result of the rule matching, the lookup engine returns a response message indicating whether a match is found.