Refer to the exhibit.

From the exhibit, we notice network 172.29.0.0/16 was learned via two routes:

+ From 192.168.254.2 with FD = 307200 and AD = 281600

+ From 192.168.253.2 with FD = 410200 and AD = 352300

The first route is installed into the RIB as the successor route because of lower FD.

When the first route fails, router will not use the second route as it does not satisfy the feasibility condition. The feasibility condition states that, the Advertised Distance (AD, also called the reported distance) of a route must be lower than the feasible distance of the current successor route.