Routing Protocol Concepts and Configuration

The United States Postal Service routes a huge number of letters and packages each day. To do so, the postal sorting machines run fast, sorting lots of letters. Then the letters are placed in the correct container and onto the correct truck or plane to reach the final destination. However, if no one programs the letter-sorting machines to know where letters to each ZIP code should be sent, the sorter cannot do its job. Similarly, Cisco routers can route many packets, but if the router does not know any routes—routes that tell the router where to send the packets—the router cannot do its job.