The router is the first device that you will work with that is at the OSI network layer, or otherwise known as Layer 3. However, because of their ability to route packets based on Layer 3 information, routers have become the backbone of the Internet, running the IP protocol.
Routers are the most important traffic-regulating devices on large networks.
While performing these basic functions, routers can also execute many other tasks that are covered in later chapters. A router can have many different types of interface ports. Figure shows a serial port which is a WAN connection. The graphic also shows the console port connection which allows direct connection to the router to be able to configure it. Figure shows another port interface type.