VRRP and HSRP pre-empt

dkblee · ‎07-18-2007

hi! I'm not very clear about the pre-empt command usage in VRRP and HSRP.

In HSRP, can the pre-empt command be used in the active, standby and listening router? or just applicable on the active router?

In VRRP, i got this sample config from the ccnp bcmsn course book. I do not understand why they disable the pre-empt in the standby router. Anyone can explain on this? Thanks.

CatalystA(config)# interface vlan 50

CatalystA(config-if)# ip address 192.168.1.10 255.255.255.0

CatalystA(config-if)# vrrp 1 priority 200

CatalystA(config-if)# vrrp 1 ip 192.168.1.1

CatalystA(config-if)# vrrp 2 priority 100

CatalystA(config-if)# no vrrp 2 preempt

CatalystA(config-if)# vrrp 2 ip 192.168.1.2

CatalystB(config)# interface vlan 50

CatalystB(config-if)# ip address 192.168.1.11 255.255.255.0

CatalystB(config-if)# vrrp 1 priority 100

CatalystA(config-if)# no vrrp 1 preempt

CatalystB(config-if)# vrrp 1 ip 192.168.1.1

CatalystB(config-if)# vrrp 2 priority 200

CatalystB(config-if)# vrrp 2 ip 192.168.1.2

Richard Burts · ‎07-18-2007

David

In my experience whether preempt is appropriate on either the active or the standby routers depends on your network environment and what you want to achieve. If you are using the interface tracking it will not work without preempt on the standby router. If you have a higher priority router and you want it to become active if it goes out of service and returns to service then preempt is needed on the active router. So there are situations on both active and standby and listening routers where preempt is appropriate.

In this example I am not clear why they are configuring no vrrp 1 preempt. Its effect is that the Catalyst with that configured in a particular group will never become the active router unless its peer goes out of service.

HTH

Rick

HTH

Rick