The router will forward the packet from interface Ethernet 0 and place it on interface token ring 0. Host B will then see a token ring frame that contains its MAC address and process it. Notice that the original frame was Ethernet and the final frame is token ring encapsulating an IP packet. This is one of the powerful features of a network router. When the packet arrives on one interface and is forwarded to another, this is called layer 3 switching.
Routers maintain information about other routers in the network.
A router that is on the same network segment as another router is said to be a routing neighbor. A distance metric is assigned to the neighbor router. This distance metric is called a hop. Neighboring routers are said to be one hop away from the local router. Figure 6-3 reflects the upgraded Sprocket s LAN with routers connected to the corporate Fast Ethernet backbone.