Alcatel-Lucent 7750 SR OS - Manual (Page 183)

VRRP
7750 SR OS Router Configuration Guide Page 183
VRRP Priority Control Policy Delta In-Use Priority Limit
A VRRP priority control policy enforces an overall minimum value that the policy can inflict on
the VRRP virtual router instance base priority. This value provides a lower limit to the delta
priority events manipulation of the base priority.
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.