Static Route Selection as Backup in Dynamic Protocols

B

The correct answer is B. administrative distance.

When multiple routes to a destination exist in a routing table, the router chooses the one with the lowest administrative distance. The administrative distance is a measure of the trustworthiness of a routing information source.

A static route has an administrative distance of 1 by default, which is lower than any dynamic routing protocol. Therefore, if a dynamic protocol is being used, and a static route has been configured as a backup, the static route will not be used unless the dynamic protocol fails or loses the route to the destination.

To make the static route more attractive as a backup, you can increase its administrative distance so that it is higher than the dynamic routing protocol. This can be done using the "distance" command when configuring the static route.

For example, if a router is using OSPF as its dynamic routing protocol and has a static route configured as a backup, the default administrative distance for OSPF is 110. To make the static route more attractive, you can configure it with an administrative distance of 120 using the following command:

scssCopy code
Router(config)# ip route 10.10.10.0 255.255.255.0 192.168.1.2 120 

This way, if the OSPF route to 10.10.10.0/24 is lost, the router will select the static route as the next best option because it has a higher administrative distance.

In summary, when using a dynamic routing protocol and a static route as a backup, you can tune the administrative distance of the static route to affect its selection.