VRRP timers
Skew_Time
Skew_Time helps avoid the situation that multiple backups in a VRRP group become the master at the same time when the master in the VRRP group fails.
Skew_Time is not configurable; its value depends on the version of VRRP.
In VRRPv2 (described in RFC 3768), Skew_Time is (256 – Router priority)/256.
In VRRPv3 (described in RFC 5798), Skew_Time is ((256 – Router priority) × VRRP advertisement interval)/256.
VRRP advertisement interval
The master in a VRRP group periodically sends VRRP advertisements to declare its presence.
You can configure the interval at which the master sends VRRP advertisements. If a backup does not receive a new VRRP advertisement from the master when the timer (3 × VRRP advertisement interval + Skew_Time) expires, it regards that the master has failed and takes over as the master.
VRRP preemption delay timer
You can configure the VRRP preemption delay timer to do the following:
Avoid frequent state changes among members in a VRRP group.
Provide the backups enough time to collect information (such as routing information).
In preempt mode, a backup does not immediately become the master after it receives an advertisement with lower priority than the local priority. Instead, it waits for a period of time (preemption delay time + Skew_Time) before taking over as the master.