I need to verify a module that processes ARP packets. I want to create a testbench that inputs ARP packets, But I want to create bad packets, so need to make some of the ARP header values bad. I only want to make one of the header values bad at a time. For instance I may have the hardware type field as the correct value or a bad value. I am not sure how I would write constraints for each of the values that I want to alter. Would I need to create different versions of the packet, or can I just write constraints and then let the packets be generated with random values bad?