Implementing Cisco IP Switched Networks (SWITCH v2-0) (#93)

You have configured three routers in HSRP group 10 to provide gateway redundancy for VLAN 56. Your intention was for Router 1 to be the active router in the group and for Router 3 to be the standby router. Furthermore, in the event that Router 1 became unavailable, resulting in Router 3 becoming active, you intended for Router 1 to resume its role as active when it came back online. However, you discover that in practice, Router 1 does NOT resume the active role when it comes back online. What command should be executed on Router 1?

router1(config)# interface VLAN 56 router1(config-if)# standby 10 preempt
router1(config)# interface VLAN 10 router1(config-if)# standby 56 preempt
router1(config)# standby 10 preempt
router1(config)# standby 56 preempt