A method and system for classifying data packet fields are disclosed. They associate a final tag to each of the fields in a data packet in relation to a set of classifying rules, and involve building a decision tree using a recursive algorithm to apply the set of classifying rules on the data packet fields, mapping each node of the built decision tree respectively to a processing element of a FPGA, each processing element comprising a processor and a memory, pipelining all mapped processing elements, and processing the data packet fields through the pipelined and mapped processing elements.