VRRP Master Election

When a VRRP configured network starts, VRRP uses an election algorithm to dynamically assign master responsibility to one of the VRRP routers on the network.

The VRRP master is determined by the following factors:

If the master router becomes unavailable, the election process begins and the backup router that wins the election assumes the role of master.

Note

Note

In VRRP IPv6, master election happens based on the interface link local address when the priorities are the same. The highest link local address switch is selected as the VRRP master.

A new master is elected when one of the following things happen:

If VRRP is disabled on the master interface, the master router sends an advertisement with the priority set to 0 to all backup routers. This signals the backup routers that they do not need to wait for the master down interval to expire, and the master election process can begin immediately.

The master down interval is set using the following formula: 3 x advertisement interval + skew time.

The advertisement interval is a user-configurable option, and the skew time is (256-priority/256).

Note

Note

The formula for VRRPv2; ((256 - priority) / 256). The VRRPv3 Skew time calculation will be different. Please refer to RFC 5798 (http://tools.ietf.org/html/rfc5798), Skew time. (((256 - priority) x Master_Adver_Interval) / 256)
Note

Note

An extremely busy CPU can create a short dual master situation. To avoid this, increase the advertisement interval.