Company seldom uses a single router to connect its entire network for two purpose.

• Because the router must transmit every packet, the processor in a provided router is insufficient to manage the traffic.

• Redundancy enhanced Internet reliability.

An Internet consists of a set of networks interconnected by routers. The Internet application allows every organization to select the number and type of network, the number of routers to use to connect them, and the same interconnection method. Three routers connecting four networks in series is given in the figure below.