What Is a Router?
Like its name suggests, a router is a network device that determines how datagrams sent over the network get to their final destination. This is a very simple definition. A more accurate definition is that a router connects two networks together, and determines how datagrams get from one network to another.
A datagram is a packet of digital information. A datagram contains addressing information, as well as the data to be transmitted. Not all datagrams necessarily take the same route to get to their destinations, even if they all have the same origin.
To better understand what a router does, look at the following two figures. Figure 28.1 shows two sample networks for a fictional global company that has offices in New York ...