Implementing and Administering Cisco Solutions: Answering the Question on Route Installation

Which route is installed?


R1 has learned route via numerous routing protocols. Which route is installed?



Click on the arrows to vote for the correct answer

A. B. C. D.


When a router learns multiple routes for the same destination network via different routing protocols, the router needs to select which route to install in its routing table. The process of selecting the best route among multiple available routes is called route selection or route preference.

In this scenario, R1 has learned route via numerous routing protocols. The question is asking which route will be installed in R1's routing table.

A. Route with the next hop that has the highest IP: This is not a valid criteria for selecting the best route. The next hop IP address does not provide any indication of the route's quality or performance.

B. Route with the lowest cost: This is a valid criteria for selecting the best route in a single routing protocol. However, when multiple routing protocols are involved, the cost metric may not be comparable between different protocols.

C. Route with the lowest administrative distance: This is the most commonly used criteria for route selection when multiple routing protocols are involved. Administrative distance (AD) is a Cisco-specific attribute that represents the trustworthiness of the routing source. A route learned from a more trusted source (such as a directly connected network) will have a lower AD than a route learned from a less trusted source (such as a routing protocol). The route with the lowest AD will be installed in the routing table.

D. Route with the shortest prefix length: This is a valid criteria for selecting the most specific route (i.e., the route with the longest prefix match) when multiple routes with different prefix lengths are available. However, in this scenario, all routes have the same prefix length (24), so this criteria does not help to differentiate between them.

Therefore, the correct answer is C: route with the lowest administrative distance.