Hi Vlad,
Try this:
ip route 8.8.8.8 255.255.255.255 Ethernet0/0 10.0.0.1
ip route 8.8.8.8 255.255.255.255 Null0 2
!
ip sla 1
icmp-echo 8.8.8.8 source-interface Ethernet0/0
threshold 800
timeout 1000
frequency 30
!
ip sla schedule 1 start-time now life forever
!
track 1 rtr 1 reachability
!
ip route 0.0.0.0 0.0.0.0 10.0.0.1 track 1
ip route 0.0.0.0 0.0.0.0 20.0.0.1 2
The first two static routes are there to make sure that the tested IP address inside the ISP1 is truly reached only via link to ISP1, and if that link is down, then the pings are going to be thrown away (this is to prevent pinging 8.8.8.8 via ISP2 thanks to the default route).
Then there is the configuration of the IP SLA probe. It will ping the 8.8.8.8 using the source IP taken from E0/0 each 30 seconds. The ping will be considered over threshold but still successful if it returns in more than 800 msec (we won't be using this result anyway), and will be considered unsuccessful if it does not return in 1000 msec. Then, the IP SLA probe is scheduled to start immediately and to run continuously.
Subsequently, we create a track object. The track object is an interface between the IP SLA probe and its "users", in this case, the static route. When different subsystems in IOS perform tracking, they refer to track objects, and the track objects in turn hold the state of the particular test or probe they are associated with. In this case, the track object 1 will hold the result of the IP SLA probe 1.
And finally, we create two static default routes. The first one is through ISP1 but is subjected to a successful result stored in the track object 1. If the track object 1 reports failure, this route will be removed from the routing table and replaced with the backup default route that has worse administrative distance.
Please note that the IP SLA syntax has changed considerably in the recent IOSes. If the current syntax is not accepted by your router please let me know, I will try to rewrite it to the "old" format.
And of course, feel welcome to ask further!
Best regards,
Peter
