Instruction Manual

Virtual Router Redundancy Protocol (VRRP)
Using the Pre-empt Delay Timer
Possible Configuration Scenarios
Preempt Delay Time = Zero Seconds. This is the default behavior. It
works in the same way that VRRP works currently.
Preempt Delay Time is Greater Than or Equal to the Master Down Time
(3 times the advertisement interval).
a. An Owner Virtual Router after reboot—waits for the Master Down
Time. If the Owner router does not receive a packet during this time,
it becomes the Master. If it receives a VRRP advertisement from its
peer during this time, it waits until the expiration of the preempt delay
time before becoming the Master.
b. A Backup Virtual Router after reboot—waits for the Master Down
Time. If the Backup router does not receive a packet during this time,
it becomes the Master. If it receives a VRRP advertisement from its
peer during this time, and it has a higher priority value than this peer,
it waits until the expiration of the preempt delay time before becom-
ing the Backup.
Preempt Delay Time is Less Than the Master Down Time.
a. Owner router—becomes the Master after expiration of the preempt
delay time.
b. Backup router—becomes the Backup after expiration of the preempt
delay time if it does not receive a VRRP advertisement from a higher
priority peer (or the Owner).
When the Preempt Delay Time is not Applicable
Once the router has rebooted and is in steady state VRRP operation, the PDT
is not applicable if:
■ The VRRP VLAN goes down and comes back up
■ The Virtual Router is disabled and re-enabled
■ VRRP is globally disabled and then re-enabled
Backward Compatibility
If a VRRP router functions with an older version that does not have the pre-
empt delay timer feature, it will take over virtual IP address control immedi-
ately on start-up or when there is a fail-back event. There should be no
backward compatibility issues.
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