Some embodiments provide a forwarding element that parses a packet to selectively extract a set of header field values for a flow key. The forwarding element then uses the flow key to find a matching flow to process the packet. In some embodiments, the forwarding element chooses the set of header values following the match pattern of a set of one or more flows. The forwarding element of some embodiments chooses the set of header values based on a wildcard mask that is associated with a flow entry or a flow table mask that is associated with a flow table.