A router is a type of internetworking device that passes data packets between networks based on Layer 3 addresses. A router has the ability to make intelligent decisions regarding the best path for delivery of data on the network. In this chapter, you will learn how routers use a Layer 3 addressing scheme to make forwarding decisions. In addition, you will learn how devices on local-area networks (LANs) use Address Resolution Protocol (ARP) before forwarding data to a destination. You will learn what happens when a device on one network does not know the MAC address of a device on another network. You will learn that Reverse Address Resolution Protocol (RARP) is the protocol a device uses when it does not know its own IP address. Lastly, you will learn the difference between routing and routed protocols and how routers track distance between locations. You will also learn about distance-vector, link-state, and hybrid routing approaches and how each resolves common routing problems. In networking, there are two addressing schemes: one uses the MAC address, a data link (Layer 2) address; the other uses an address located at the network layer (Layer 3) of the OSI model. An example of a Layer 3 address is an IP address. A router is a type of internetworking device that passes data packets between networks, based on Layer 3 addresses. A router has the ability to make intelligent decisions regarding the best path for delivery of data on the network. Bridges and switches use physical, or MAC addresses, to make data forwarding decisions. Routers use a Layer 3 addressing scheme to make forwarding decisions. They use IP, or logical addresses, rather than MAC addresses. Because IP addresses are implemented in software, and refer to the network on which a device is located, sometimes these Layer 3 addresses are referred to as protocol addresses, or network addresses. Physical, or MAC addresses, are usually assigned by the NIC manufacturer an...
