Network Layer: Address Mapping, Error Reporting, and Multicasting * A metric is the cost assigned for passage of a packet through a network. * A router consults its routing table to determine the best path for a packet. * An autonomous system (AS) is a group of networks and routers under the authority of a single administration. * RIP and OSPF are popular interior routing protocols used to update routing tables in an AIS. * RIP is based on distance vector routing, in which each router shares, at regular intervals, its knowledge about the entire AS with its neighbor. * A RIP routing table entry consists of a destination network address, the hop count to that destination, and the IP address of the next router. * OSPF divides an AS into areas, defined as collections of networks, hosts, and routers. * OSPF is based on link state routing, in which each router sends the state of its neighborhood to every other router in the area. A packet is sent only if there is a change in the neighb...