A method and system for finding a longest matching prefix for an input keyword from among multiple prefixes. The prefixes are data strings of varying lengths wherein prefixes of length n or greater are probabilistically a longest prefix match. The method of the present invention begins by mapping the prefixes of length greater than or equal to n1, that is, in the interval [n1, L], into a first lookup system. Remaining prefixes of length less than n1 but greater than or equal to n2, that is, in the interval [n2, n1−1], are mapped into a second index utilizing a second hash function, wherein n2 is less than n1. Further lookup systems on prefixes having lengths in the intervals [n3, n2−1], [n4, n3−1], and so on, may also be utilized, as determined by optimization studies and the statistics of routing tables.