An important aspect of the VRRP redundancy scheme is VRRP device priority. Priority determines the role that each VRRP device plays and what happens if the virtual device master fails.

If a VRRP device owns the IP address of the virtual device and the IP address of the physical interface, this device will function as a virtual device master.

Priority also determines if a VRRP device functions as a virtual device backup and the order of ascendancy to becoming a virtual device master if the virtual device master fails. You can configure the priority of each virtual device backup with a value of 1 through 254 using the priority command (use the vrrp address-family command to enter the VRRP configuration mode and access the priority option).

For example, if device A, the virtual device master in a LAN topology, fails, an election process takes place to determine if virtual device backups B or C should take over. If devices B and C are configured with the priorities of 101 and 100, respectively, device B is elected to become virtual device master because it has the higher priority. If devices B and C are both configured with the priority of 100, the virtual device backup with the higher IP address is elected to become the virtual device master.

By default, a preemptive scheme is enabled whereby a higher priority virtual device backup that becomes available takes over from the virtual device backup that was elected to become virtual device master. You can disable this preemptive scheme using the no preempt command (use the vrrp address-family command to enter the VRRP configuration mode, and enter the no preempt command). If preemption is disabled, the virtual device backup that is elected to become virtual device master remains the master until the original virtual device master recovers and becomes master again.

Note	Preemption of a lower priority master device is enabled with an optional delay.

The virtual device master sends VRRP advertisements to other VRRP devices in the same group. The advertisements communicate the priority and state of the virtual device master. The VRRP advertisements are encapsulated into either IPv4 or IPv6 packets (based on the VRRP group configuration) and sent to the appropriate multicast address assigned to the VRRP group. For IPv4, the multicast address is 224.0.0.18. For IPv6, the multicast address is FF02:0:0:0:0:0:0:12. The advertisements are sent every second by default and the interval is configurable.

Cisco devices allow you to configure millisecond timers, which is a change from VRRPv2. You need to manually configure the millisecond timer values on both the primary and the backup devices. The master advertisement value displayed in the show vrrp command output on the backup devices is always 1 second because the packets on the backup devices do not accept millisecond values.

You must use millisecond timers where absolutely necessary and with careful consideration and testing. Millisecond values work only under favorable circumstances. The use of the millisecond timer values is compatible with third party vendors, as long as they also support VRRPv3. You can specify a timer value between 100 milliseconds and 40000 milliseconds.

1.    enable


2.    configure terminal


3.    fhrp version vrrp v3


4.    end

Device> enable

Device# configure terminal

Device(config)# fhrp version vrrp v3

Device(config)# end

1.    enable


2.    configure terminal


3.    fhrp version vrrp v3


4.    interface type number


5.    vrrp group-id address-family {ipv4 | ipv6}


6.    address ip-address [primary | secondary]


7.    description group-description


8.    match-address


9.    preempt delay minimum seconds


10.    priority priority-level


11.    timers advertise interval


12.    vrrpv2


13.    vrrs leader vrrs-leader-name


14.    shutdown


15.    end

Device> enable

Device# configure terminal

Device(config)# fhrp version vrrp v3

Device(config)# interface GigabitEthernet 0/0/0 

Device(config-if)# vrrp 3 address-family ipv4 

Device(config-if-vrrp)# address 100.0.1.10 primary 

Device(config-if-vrrp)# description group 3 

Device(config-if-vrrp)# match-address 

Device(config-if-vrrp)# preempt delay minimum 30 

Device(config-if-vrrp)# priority 3 

Device(config-if-vrrp)# timers advertise 1000 

Device(config-if-vrrp)# vrrpv2 

Device(config-if-vrrp)# vrrs leader leader-1 

Device(config-if-vrrp)# shutdown 

Device(config)# end

1.    enable


2.    configure terminal


3.    fhrp version vrrp v3


4.    interface type number


5.    fhrp delay {[minimum] [reload] seconds}


6.    end

Device> enable

Device# configure terminal

Device(config)# fhrp version vrrp v3

Device(config)# interface GigabitEthernet 0/0/0 

Device(config-if)# fhrp delay minimum 5 

Device(config)# end