Routers require fast and flexible route table lookup for incoming packets at relatively low cost.This paper describes a software-based route cache algorithm for network processors.Part of the on-chip high-speed memory space is allocated and programmed into a caching table for temporal storage of route lookup results.A suitable hash function can make a good balance between cache miss rate and update complexity,which shortens the average search time,reduces the contentions on memory bus and leaves more headroom for other network applications.Experiments with real-life packet traces show that the packet throughput of a network processor can be greatly improved with only a small number of route cache entries per processing element.