A packet processing system comprises a packet processing graph comprising classifier nodes including a root classifier node and leaf classifier nodes. The root classifier node is connected to each of the classifier nodes through a respective packet processing path in the graph. Each classifier node stores node match data indicative of at least one match to be applied by the respective classifier node. The classifier nodes comprise first and second classifier nodes arranged in a first packet processing path of said plurality of packet processing paths. The first classifier node stores node match data indicative of a match corresponding to content from a plurality of packet header field types, including first and second, different packet header field types. The second classifier node stores node match data indicative of a match corresponding to content from at least one packet header field type, including the first packet header field type.