[Reference: https://www.cisco.com/c/en/us/support/docs/ip/ip-routing/200785-ISP-Failover-with-default-routes-using-I.html, In the above configuration we have not had activated our IP SLA operation. We can start it with, this command:, R1(config)#ip sla schedule 100 life forever start-time now, Also we should specific the rate of ICMP echo:, R1(config-ip-sla-echo)#frequency 5 // Send ICMP echo every 5 seconds, , , , , , ]