VRRP Components
376 Router Configuration Guide
Skew Time
The skew time is used to add a time period to the master down interval. This is not a
configurable parameter. It is derived from the current local priority of the virtual router’s
VRID. To calculate the skew time, the virtual router evaluates the following formula:
For IPv4: Skew Time = ((256 - priority) / 256) seconds
For IPv6: Skew Time = (((256 - priority) * Master_Adver_Interval) / 256) centiseconds
The higher priority value, the smaller the skew time will be. This means that virtual routers
with a lower priority will transition to master slower than virtual routers with higher
priorities.
Master Down Interval
The master down interval is a calculated value used to load the master down timer. When the
master down timer expires, the virtual router enters the master state. To calculate the master
down interval, the virtual router evaluates the following formula:
Master Down Interval = (3 x Operational Advertisement Interval) + Skew Time
The operational advertisement interval is dependent upon the state of the inherit parameter.
When the inherit parameter is enabled, the operational advertisement interval is derived from
the current master’s advertisement interval field in the VRRP advertisement message. When
inherit is disabled, the operational advertisement interval must be equal to the locally
configured advertisement interval.
The master down timer is only operational when the local virtual router is operating in backup
mode.
Preempt Mode
Preempt mode is a true or false configured value which controls whether a specific backup
virtual router preempts a lower priority master. The IP address owner will always become
master when available. Preempt mode cannot be set to false on the owner virtual router. The
default value for preempt mode is true.
When preempt mode is true, a master non-owner virtual router will only allow itself to be
preempted when the incoming VRRP advertisement message priority field value is one of the
following:
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