nd disparate Layer 2 network types, and because it is a Layer 3 LAN Interconnection and Internetworking Campus 3 Campus 4 Campus 2 WAN Router WAN Router Core Network WAN Router Campus 1 Building 1 Building 6 Building 2 Building 3 Building 4 Building 5 Figure 6.13 An example of routers in a network device, a router is networkable-it understands how to read network addresses and how to select the destination or target network, SO it limits broadcast storms by not propagating them. This capability allows routers to act as firewalls between LAN segments. Routers can be associated with traffic filtering and isolation, and because they can read information about the network and transport protocols used, they can make forwarding decisions. Routers can make linking and rerouting decisions, which makes possible selec- tive routing of individual packets over multiple communication paths. Remember that bridges have to disable all but one path, whereas a router can decide on-the-fly between numerous communications paths. The path a router selects depends on the user's requirements, including cost, speed, and priority. Routers are protocol specific, but modern routers support multiple protocols, such as TCP/IP or IPX/SPX (the network and transport layer protocols used in Novell's NetWare network operating system). The key is that each of the protocols a router supports for internetworking requires its own separate routing table, SO the more protocols the router supports, the more complex, memory intensive, and expensive it is due to the size and stability of the associated routing tables. Routers can be used as bridges to connect similar and dissimilar networks, and they are often applied as firewalls. Chapter 6 Local Area Networking The functions of a router are as follows: Learning-A router learns who its neighbors are and builds a forwarding table based on their addresses. Filtering-A router forwards traffic by looking at its routing table for the next hop. Routing and switching-A router selects the best destinations based