How to set up backup routes?

Question

Cisco

According to the task, it is necessary to configure backup network routes in case of failure of one of the devices. How do I set up backup routes if I have RIPv2?
Now both routers have the same ip when connecting to the server switch (L3 also with subnets), but when the left router or L3 is disconnected, the packets do not go through.

Answer 1

"I have both routers have the same ip" - SHO?
Between 3560 - in all accessory vlans (only in them) you configure VRRP
Between routers in vlan 100 towards servers, too, VRRP.
Between all L3-devices - p2p links, RIP on them.
As a result, there will be no identical IPs anywhere, I don’t understand what it is and why it is.