1. A system having a plurality of network devices, each of the plurality of network devices comprising: an interface module including a plurality of physical ports to transmit and receive packets; a computing module configured to execute a computing process with a computational expression using seed information, the seed information including at least one of destination information and source information associated with a received packet; a destination search module configured to, based on the result of the computation, select a physical port for transmission of the received packet from a plurality of candidate ports among the plurality of physical ports; and a modifying module configured to modify the computational expression, wherein the plurality of network devices include a preceding-stage network device and a subsequent-stage network device, the subsequent-stage network device being directly coupled to the preceding-stage network device with physical wiring, and wherein the subsequent-stage network device and the preceding-stage network device are configured to use different expressions in the computing process.