A method for providing a parser by a network node, which includes a table defining a plurality of rules and a plurality of match fields required for extraction from an incoming data packet header in order to apply each of the respective rules is described. The method comprises determining at least one occurrence in the table of a first match field that requires extraction; and determining a parser for use in accordance with the at least one determined occurrence of the first match field. Furthermore, the step of determining at least one occurrence of the first match field comprises initializing a counter associated with the first match field and incrementing the counter for each of the plurality of rules that requires extraction of the first match field. And the step of determining a parser comprises determining the parser for use in accordance with the counter. A network node for carrying this method is also described.