An exact-match flow table structure stores flow entries. Each flow entry includes a Flow Id and an action value. A flow entry is generated from an incoming packet. The flow table structure determines whether there is a stored flow entry, the Flow Id of which is an exact-match for generated Flow Id. In one novel aspect, a multiplexer circuit is used to generate Flow Ids. The multiplexer circuit includes a plurality of byte-wide multiplexer. Each respective one of the byte-wide multiplexers outputs a byte that is a corresponding respective byte of the Flow Id. The various inputs of the byte-wide multiplexers are coupled to receive various bytes of the incoming packet, various bytes of modified or compressed packet data, as well as bytes of metadata. By controlling select values supplied onto the select inputs of the multiplexer circuit, Flow Ids of different forms can be generated.