Abstract: A network unit includes a forwarding database which includes entries relating packet addresses to forwarding data and is operative to form linked chains of entries wherein the entries in a chain represent different packet addresses which are reduced by hashing to the same pointer for the database. A seed for a hashing algorithm is provided by a combination, such as an exclusive-OR combination, of part of an input address word and a selected word. Hashing is preferably performed in at least two cycles, wherein in one cycle a hash function is applied to a portion of the input address not including the part which is combined with the selected word to constitute a hash seed and in another (preceding) cycle a further part of the address and the aforementioned hash seed are subject the hash function.