Associative memory having a mask function for use in network devices and network system

A network device possessing a means, determining a transfer permission of said input transfer data with reference to an match state in search operation for a single or plural transfer rule, using an issuer network address and a destination network address annexed to an input transfer data as search data, said transfer rule wherein said network device which stores a transfer rule table to indicate a mask information representative of whether or not every single bit or every plural bits of said storage data should be excluded from a search object, for every storage data including a bit field corresponding to each component, information of transfer permission, and said single or plural transfer rule, said transfer rule possessing, when all bits of determination input data are in a primary searching operation, said primary searching operation taking said mask information into account in order to exclude single or plural bits of said storage data from a search object when said corresponding mask information is in a valid state of mask information for each single word, a primary searching means to produce a primary distinguishing signal to distinguish a selected word, said network device possessing an intermediate data producing means which supply an intermediate data produced by a logical operation of the storage data corresponding to words holding a selected state, a logical operation of the mask information corresponding to said words, and a logical operation of a single or plural pairs of external search data, said network device possessing a single or plural shared secondary searching means when each partial bit field of divided said intermediate data are supplied, similar to a composition of partial bit fields of said determination input data, controlling whether or not a secondary search operation is to be carried out for only a bit field of said storage data or mask information corresponding to said partial bit fields in transfer rule, with reference to a state of secondary search controlling signal, and producing a secondary identification signal for identifying a particular transfer rule selected from said search operation, said network equipment memory possessing means producing said secondary search controlling signal in order to carry out said secondary search operation using said partial bit field of said intermediate data upon completion of said primary search operation using all bit fields of said determination input data as search data, said network device possessing a determination means to determine a transfer permission of said input transfer data, with reference to information of transfer permission with said match signal.