Thanks a lot for the explanation Rene.
I would like you to clarify one more thing.
For the LAN segment: 192.168.100.0 : R1 is the active router to reach 8.8.8.8 and R2 is the standby as the priority for R1 is 150.
I am not using interface for tracking as i want the failover to happen on the basis of reachability of 8.8.8.8.
I have set a tracking object with IP SLA1 for type: echo to ping 8.8.8.8 and mapped it with Standby 1 on R1 to decrement priority by 90 if the ping fails.
To verify this, I did a “Shut” on the interface of R1 connecting to R3, what happened is as follows :
R1 was learning one more route towards 8.8.8.8 from R2 (ibgp), that route starts being used and the reachability from R1 towards 8.8.8.8 again gets restored, hence preemption takes place which makes R1 again an Active router.
Am i doing something wrong here, or should i setup a route map from R2 towards R1 to deny advertising 8.8.8.8 route to R1.
Please explain. Thanks in advance. 