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are cisco certifications worth it.1.2 Basic Contents 191Rl IP routing table R2IP routing tableg0/0 -172.30.11.0/24 172.30.1.0/24S0/1/0so/o 172.30.1.2 G0/0-172.30.21.0/24RIP update day 172.30" 1.0,metric 1 |-A30 secondsRIP update II | 172.30.11.0,metric 1 |->Figure 9.5 Common balancing states RIP operation: complete update via horizontal split In addition, take some time to focus on the route obtained in step 4: the bold route in the R1 routing table. This route is the route obtained from R2 to reach 172.30.22.0/24. It shows R1's local S0/0 interface as the output interface because R1 received an update on that interface. It also lists R2's serial IP address 172.30.1.2 as the next-hop router, because that's the IP address where R1 gets that route. Next, look at the bottom of that diagram, that's where the RIP update message is being used to monitor the status of the neighboring router. The router repeats the exact same update message every 30 seconds. Note that in an Internet network, if nothing changes in a year, with RIP in use, then the routers will repeat the same routing information between each other every 30 seconds. Why? If the router does not receive an update message within a predefined period, then the local router knows that that neighboring router is no longer working. Finally, the diagram is an example of a horizontal split. Notice that both routers have all four subnets listed in their IP routing tables, while the RIP update message does not list the four subnets. Why? Horizontal segmentation. Horizontal splitting is a feature of DV that tells the routing protocol not to inform certain routes in updates sent through an interface, that is, routes that are shown as output interfaces for that interface. Those routes that are not told on an interface typically include routes that are obtained from routing updates received on that interface. It's hard to figure out what a horizontal split is by reading alone, but it's easier when you look at the examples. Figure 9-6 continues the example from Figure 9-5, but the focus of attention is on the RIP updates sent to R2's R1 through R1's S0/0 interface. This figure shows three brightly colored routes in R1's routing table, all of which show S0/0 as the outgoing interface. The horizontally split canonical high-speed R1 ignores to those bright-colored routes when creating RIP updates that are sent out through S0/0. Only the bold routes (which do not have S0/0 listed as the outgoing interface) can be included in RIP updates sent out through S0/0.Figure 9.6 R1 does not advertise three routes due to horizontal split