Alcatel-Lucent 7750 SR OS - Manual (Page 176)

VRRP Components
Page 176 7750 SR OS Router Configuration Guide
Message Interval and Master Inheritance
Each virtual router is configured with a message interval per VRID within which it participates.
This parameter must be the same for every virtual router on the VRID.
The default advertisement interval is 1 second and can be configured between 1 and 255 seconds in
1 second increments.
As stated in RFC 2338, the advertisement interval field in every received VRRP advertisement
message must match the locally configured advertisement interval. If a mismatch occurs, the
incoming message is discarded without further processing. An optional inherit parameter specifies
that the current master’s advertisement interval setting should operationally override the locally
configured advertisement interval setting. If the current master changes, the new master setting is
used. If the local virtual router becomes master, the locally configured advertisement interval is
enforced.
If a VRRP advertisement message is received with an advertisement interval set to a value
different than the local value and the inherit parameter is disabled, the message is discarded
without processing.
The master virtual router on a VRID uses the advertisement interval to load the advertisement
timer, specifying when to send the next VRRP advertisement message. Each backup virtual router
on a VRID uses the advertisement interval (with the configured local priority) to derive the master
down timer value.
Skew Time
The skew time is used to add a sub-second 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:
Skew Time = ((256 - priority) / 256) seconds
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.