VRRP Priority Control Policies
382 Router Configuration Guide
A delta priority event is a conditional event defined in the priority control policy that subtracts
a given amount from the current, in-use priority for all VRRP virtual router instances to which
the policy is applied. Multiple delta priority events can apply simultaneously, creating a
dynamic priority value. The base priority for the instance, less the sum of the delta values
derives the actual priority value in-use.
An explicit priority event is a conditional event defined in the priority control policy that
explicitly defines the in-use priority for the virtual router instance. The explicitly defined
values are not affected by the delta in-use priority limit. When multiple explicit priority
events happen simultaneously, the lowest value is used for the in-use priority. The configured
base priority is not a factor in explicit priority overrides of the in-use priority.
The allowed range of the Delta In-Use Priority Limit is 1 to 254. The default is 1, which
prevents the delta priority events from operationally disabling the virtual router instance.
VRRP Priority Control Policy Priority Events
The main function of a VRRP priority control policy is to define conditions or events that
impact the system’s ability to communicate with outside hosts or portions of the network.
When one or multiple of these events are true, the base priority on the virtual router instance
is either overwritten with an explicit value, or a sum of delta priorities is subtracted from the
base priority. The result is the in-use priority for the virtual router instance. Any priority event
may be configured as an explicit event or a delta event.
Explicit events override all delta events. When multiple explicit events occur, the event with
the lowest priority value is assigned to the in-use priority. As events clear, the in-use priority
is reevaluated accordingly and adjusted dynamically.
Delta priority events also have priority values. When no explicit events have occurred within
the policy, the sum of the occurring delta events priorities is subtracted from the base priority
of each virtual router instance. If the result is lower than the delta in-use priority limit, the
delta in-use priority limit is used as the in-use priority for the virtual router instance.
Otherwise, the in-use priority is set to the base priority less the sum of the delta events.
Each event generates a VRRP priority event message indicating the policy-id, the event type,
the priority type (delta or explicit) and the event priority value. Another log message is
generated when the event is no longer true, indicating that it has been cleared.
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