RIP Reliable Default Route with IP SLA

Topology

Hello Rene,

In this topology I, am tracking 8.8.8.8 which is hosted on R5 using a track 1 on R1 which is being called in Standby 1 to decrement priority by 90.

when i am running a continous ping to 8.8.8.8 from PC1, Serial interfaces on all the routers in the path starts flapping.

Even when i run a ping to Serial interface of R3 from PC1, Both R1 and R3 starts flapping.

I tried to change the bandwidth of the serial interfaces but no it was of no help.

I have attached router logs of R1 and R2 along with the config, Please have a look to findout what’s going wrong. Thanks