![]() R1 is also directly connected to R5 and we're running RIP everywhere, so it will form an adjacency with R5 as well. If we look at the information that reached R4 from R3, R3 told it that "You can get to the 10.0.1.0/24 network through me and it's going to be three hops." That was along the top path. R3 will then pass that information on to R4, and it will tell R4, "You can get to 10.0.0.0/24 through me. So R2 will say "Hey, R3, you can get to these networks via me. It will then pass the information on to R3. ![]() R2 will get that information and it will update its routing table. 10.1.3.0/24 is behind R5 and 10.1.2.0/24 is behind R4 from R1's point of view so they have an additional one or two hops away. R1 has formed an adjacency with R2 and it will say that "Okay, R2, you can get to these networks via me. Let's go through an example of how the metric is going to work in RIP. It is used in really small networks or in test environments. It will always use the path with the shortest hop count even if those links are low bandwidth links which would really not be the best path.īecause of the scalability limitation and the inconsideration of the links’ bandwidth, RIP is not normally used in production networks. RIP will prefer the bottom path because it will take two hops to go from R4 to R5 to R1, rather than three hops going via R3, R2, and R1. The links going down via R5 are all 10 megabits per second links. From R4, all the links in the top path are a hundred megabits per second links. In the example below, we've got network 10.0.1.0/24 connected behind R1. Therefore, there is a scalability limitation with RIP. Paths that are more than 15 hops away are marked as unreachable by default. The default maximum hop count in RIP is 15. Hop count is the number of routers the router has to go through to get to the destination network. A hop means going through another router. The Routing Information Protocol (RIP) always uses hop count as the metric. Let's take a look at the different methods and metrics that are used by our different routing protocols. If anything changes on the network, the routing tables will be updated to reflect the changes. This is a big advantage of the dynamic routing protocols, they're self-healing. The route that has the next lowest metric will be chosen, if one is available. If the best path to a destination is lost, for example, a link went down, it will be removed from the routing table and will be replaced with the next best route. Each router will take that information and then use it to make an independent calculation of its own best path to get to each destination. ![]() Link state routers advertise all the links in the area of the network to each other.Distance vector routers advertise to each other the networks they know about and their metric to get to each of them.Remember, the lower the cost or the lower the metric, the more preferred the path is going to be. Just like when you go shopping, the lower the cost of something, the better it is. The path with the lowest metric value is the most preferred path.Īn easy way to remember this is, in OSPF, the term for metric is cost. Thus, the different interior gateway protocols need some way to determine which is the best path by using different calculation methods.Įach possible path will be assigned a metric value by the routing protocol which indicates how preferred the path is. Out of all the paths that the router knows about, only the best path is going to make it into the routing table and be used.
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