1. A network device, comprising: a plurality of ports configured to receive and to transmit packets on a network; a packet processing pipeline comprising a plurality of hardware stages including a first hardware stage and a second hardware stage, wherein the first hardware stage is configured to extract first data from first header information in a received packet and output a data structure comprising a field that includes the first data, wherein the first header information conforms to a first communication protocol, and the data structure is associated with the packet; a configurable processor coupled to the packet processing pipeline, wherein the configurable processor is configured to modify the data structure to generate a modified data structure including overwriting the field in the data structure with second data extracted from second header information in the received packet, wherein the second header information conforms to a second communication protocol that is not recognized by the first hardware stage and the second hardware stage of the packet processing pipeline; and wherein the second hardware stage is configured to perform a packet processing operation on the data structure using the data in the field of the data structure and receives the modified data structure from the configurable processor such that the second hardware stage uses the second data extracted from second header information that conforms to the second communication protocol that is not recognized by the second hardware stage.