Cisco IOS Cookbook, 2nd Edition

Using HSRP Preempt

Problem

You want to ensure that a particular router is always selected as the “active” HSRP router, whenever it is up and functioning.

Solution

You can ensure that a particular router is always selected as the HSRP active router if it is available. On the router that you wish to make your primary active HSRP router, you need to set a higher priority level and use the standby preempt command:

Router1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#interface FastEthernet 0/1
Router1(config-if)#standby 1 ip 172.22.1.1   
Router1(config-if)#standby 1 priority 120    
Router1(config-if)#standby 1 preempt     
Router1(config-if)#exit
Router1(config)#end
Router1#

The only difference on the second router is the HSRP priority level. The lower priority in conjunction with the standby preempt command forces the second HSRP router to remain in a standby state unless the primary router becomes unreachable. Then, when the primary router becomes available again, the secondary router will relinquish its role and allow the primary router to take over as the active HSRP router:

Router2#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router2(config)#interface FastEthernet 1/0
Router2(config-if)#standby 1 ip 172.22.1.1   
Router2(config-if)#standby 1 priority 110    
Router2(config-if)#standby 1 preempt       
Router2(config-if)#exit
Router2(config)#end
Router2#

You can also configure this feature by specifying the preempt keyword ...