Cisco CCNA Exam: Router Routing Table Installation

Routing Table Installation

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A router has learned three possible routes that could be used to reach a destination network. One route is from EIGRP and has a composite metric of 20514560.

Another route is from OSPF with a metric of 782. The last is from RIPv2 and has a metric of 4. Which route or routes will the router install in the routing table?



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A. B. C. D. E.


The router will use a process called "route selection" or "route determination" to decide which route(s) to use to reach the destination network. The process works by comparing the metrics of each available route, and selecting the route with the lowest metric.

In this case, there are three routes available, each learned from a different routing protocol. The metrics for each route are:

  • EIGRP: 20514560
  • OSPF: 782
  • RIPv2: 4

Since RIPv2 has the lowest metric, it would be the preferred route for the router to use. However, it is important to note that this is only the case if all three routes are equally viable (i.e., have the same administrative distance).

Administrative distance is a value assigned to each routing protocol that indicates how trustworthy it is. For example, a directly connected route has an administrative distance of 0, since it is the most reliable source of information about a network. In this case, we don't have any information about the administrative distances of the three protocols, so we can assume that they are all equal.

If that is the case, then the answer would be option C: the OSPF and RIPv2 routes. OSPF has a lower metric than EIGRP, so it would be preferred over the EIGRP route. However, since RIPv2 has an even lower metric than OSPF, it would be the route that is installed in the routing table.

It is also worth noting that it is possible for multiple routes to be installed in the routing table, if they have the same lowest metric. In this case, both the OSPF and RIPv2 routes would be installed in the routing table.