Implementing Cisco IP Switched Networks (SWITCH v2-0) (#420)

Routers R1 and R2 are configured for HSRP as shown below: Router R1: interface ethernet 0 ip address 20.6.2.1 255.255.255.0 standby 35 ip 20.6.2.21 standby 35 priority 100 interface ethernet 1 ip address 20.6.1.1.2 255.255.255.0 standby 34 ip 20.6.1.21 Router R2: interface ethernet 0 ip address 20.6.2.2 255.255.255.0 standby 35 ip 20.6.2.21 interface ethernet 1 ip address 20.6.1.1.1 255.255.255.0 standby 34 ip 20.6.1.21 standby 34 priority 100 You have configured the routers R1 & R2 with HSRP. While debugging router R2 you notice very frequent HSRP group state transitions. What is the most likely cause of this?

physical layer issues
no spanning tree loops
use of non-default HSRP timers
failure to set the command standby 35 preempt