A method of routing data through a router in a communications network, the method comprising receiving one or more data packets, each packet having a respective destination address and applying a lookup algorithm to each packet, said lookup algorithm being arranged to determine a respective route along which each packet is to be transmitted towards its destination address by searching an associated hierarchical data structure containing routing information for each packet. The method comprising forwarding each packet for transmission to its respective destination address, wherein said lookup algorithm comprises an adaptive learning component that is configured to dynamically identify an optimum starting position for searching within said hierarchical data structure, for each of the data packets, based on the results of one or more earlier searches.