HSRP is a protocol in a redundant network design. If the main router fails, the backup router will step up at taking charge of routing decisions until the main router comes back.
HRSP will activate in case of:
1. The physical MAIN router is not operational (Shutdown/No-power)
2. The interface facing to our network is down (e0/1 in the example above)
What if the R1 interface e0/0 suddenly malfunctions? or the ISP2 router accidentally shuts down?
Does our HSRP will activate?
The answer is NO because HSRP only track its interface facing our network if it’s in
Up or Downstate.
We can resolve this with the help of TRACKING OBJECT.
In the topology above both ISP1 and ISP2 advertised a static default route to our Main and Backup router. We want to track that default route reachability (0.0.0.0/32).
R1
Router(config)#track 5 ip route 0.0.0.0/32 reachability
Router(config)#int e0/1
Router(config-if)#standby 5 ip 192.168.1.1
Router(config-if)#standby 5 preempt
Router(config-if)#standby 5 priority 150
Router(config-if)#standby 5 track 5 decrement 60
R5
Router(config)#int e0/1
Router(config-if)#standby 5 ip 192.168.1.1
Router(config-if)#standby 5 preempt
We can add another Tracking Object for the R1 e0/0 interface.
If the default route disappear in the main router routing table the tracking object will activate and decrement the HSRP priority value.