Internet Routing Protocols
William Johnston Buchanan · 1999
Routers filter the network traffic so that the only traffic that flows into and out of a network is required to go into a network. In many cases there are several possible routes that can be taken between two nodes on different networks. Consider the network in Figure 18.1. In this case the upper network shows the connection between two nodes A and B through routers 1 to 6. It can be seen from the lower diagram that there are four routes that the data can take. To stop traffic taking a long route or even one that does not exist, each router must maintain a routing table so that it knows where the data must be sent when it receives data destined for a remote node.