A network unit for the reception and forwarding of data packets and for use in a stack of similar units includes a data processor and cascade control logic for the exchange of control frames with others of said units in the stack. The cascade control logic is operative to cooperate by means of the control frames in an automatic process for incrementally applying stack numbers to the units in the stack. The cascade control logic can retain a stack number in storage and the data processor is operative to execute a program to apply to the network unit and the other units progressive stack numbers which accommodate previously applied and retained stack numbers. The network unit can act as a master applying the program to the other units and as a slave whereupon it receives a stack number determined by another unit in the stack. The program may determine the validity of a set of numbers applied to units in the stack by computing the aggregate of numbering gaps between numbered units and comparing the aggregate with a predetermined maximum. The program distinguishes between units which are in an automatic numbering mode and a non-automatic numbering mode and disregards units in the non-automatic numbering mode in the application of progressive stack numbers.