Circuitry for determining network operations in a network device

A network processor for determining one or more network operations to be performed on a packet of data in a network comprises processing circuitry and protocol indicator circuitry. The packet of data contains information populating a plurality of protocol header fields. Moreover, the protocol indicator circuitry comprises a plurality of memory elements, each memory element associated with a protocol header field in the plurality of protocol header fields. The processing circuitry determines the one or more network operations to be performed on the packet of data at least in part by addressing one or more lookup tables with the contents of a subset of the plurality of protocol header fields in the packet. This subset is determined by reference to the memory elements in the protocol indicator circuitry. Each memory element is capable of being programmed to indicate whether the associated protocol header field is to be utilized by the processing circuitry in addressing the one or more lookup tables.