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In network processor (NP) application of Gigabit Ethernet (GE), the second layer design has to deal with ARP protocol; we present an approach in this paper to meet the high speed performance requirement to ARP lookup. Unlike longest prefix matching lookup algorithm widely used in IP routing lookup and flow classification, ARP lookup utilizes fixed length matching lookup algorithm, which is commonly implemented by hashing in software or directly by CAM in hardware without the need of much optimization. The algorithm proposed in this paper belongs to closed double hashing algorithm. In ARP lookup system, to solve the indeterminacy of lookup time, a two-stage queue is used to ensure the sequence of IP flows with the same destination address maintains during ARP lookup process. The performance of the system is guaranteed by experimental results under worst-case condition, which is capable of meeting the requirement of ARP lookup in GE environment. Our results show that the algorithm saves much storage and timing cost while achieving wire-speed lookup required by GE.