ccna2 chapter 1

ccna2 chapter 1.2. Compare the routes advertised by Router A and Router C with the routes already in the routing table. 3. Add 10.0.0.0 and 192.168.3.0, because they are not in the routing table. 4. Ignore 192.168.1.0 advertised by Router A and 192.168.2.0 advertised by Router C, because the metric values for these routes areThe metric value of these routes is 1, and the metric value of the corresponding entry in the routing table is 0See Figure 14.2, at this point the router converged? Don't forget the definition of convergence: the router knows the complete network topology. By this definition, the router has not yet converged. Router A's routing table does not contain 192.168.3.0, and Router C's routing table does not containHowever, Router B has converged, but Router A and Router C still need to be informed of other routes.After the periodic timer expires, the routers will again generate local routing broadcasts on the interfaces: the entire routing table is broadcast on these interfaces. Figure 14.3 shows what happens to these routers after they process these new updates. After the routers receive the updates, they will perform the steps described earlier. Note that Router A's routing table now contains 192.168.3.0, which has a hop count of 2, while Router C's routing table contains 10.0.0.0, which also has a hop count of 2 O Both of these routers learned about these networks from Router B; on Router B, these networks have a hop count of 1. Upon receiving Router B's routing table, these edge routers increase the hop count of these networks to 2 OFigure 14.3 Convergence Example - After Second Routing UpdateFrom the routing table shown in Figure 14.3, it is clear that all routers have converged. The problem, however, is that the convergence occurred after the second update. The first update was performed after the interface was active, and the second update was 60 seconds later. Therefore, in this example, the convergence time is more than 60 seconds. Conceivably, if there are hundreds of routers in the network, it could take many minutes for the network to converge, at which point each router is informed of all the reachable target networks.Let's take this network as an example, but suppose that Router A's interface E0 fails, causing Router A to be unable to connect to network 10.0.0.0, as shown in Figure 14.4. It is clear from this that Router A's routing table indicates that this network is unreachable, but unfortunately it cannot advertise this information to the rest of the network until after the periodic timer expires.After the timer expires, Router A advertises its routing table to Router B, as shown in Figure 14.5. After receiving this update, Router B converges. However, Router C does not yet have information about the latest topology, and it needs to wait until Router B's periodic timer expires before it can receive Router B's latest routing table.Routing Table for Router A Routing Table for Router B Routing Table for Router C