Editing Virtual Router Redundancy Protocol (section)

==Elections of primary/active routers==
A failure to receive a multicast packet from the primary/active router for a period longer than three times the advertisement timer causes the secondary/standby routers to assume that the primary/active router is dead. The virtual router then transitions into an unsteady state and an election process is initiated to select the next primary/active router from the secondary/standby routers. This is fulfilled through the use of multicast packets.

Secondary/standby router(s) are only supposed to send multicast packets during an election process. One exception to this rule is when a physical router is configured with a higher priority than the current primary/active, which means that on connection to the network it will pre-empt the primary/active status. This allows a system administrator to force a physical router to the primary/active state immediately after [[booting]], for example when that particular router is more powerful than others within the virtual router. The secondary/standby router with the highest priority becomes the primary/active router by raising its priority above that of the current primary/active. It will then take responsibility for routing packets sent to the virtual gateway's MAC address. In cases where secondary/standby routers all have the same priority, the secondary/standby router with the highest IP address becomes the primary/active router.

All physical routers acting as a virtual router must be in the same [[local area network]] (LAN) segment. Communication within the virtual router takes place periodically. This period can be adjusted by changing advertisement interval timers. The shorter the advertisement interval, the shorter the [[Black_hole_(networking)|black hole]] period, though at the expense of more traffic in the network. Security is achieved by responding only to first [[Hop_(networking)|hop]] packets, though other mechanisms are provided to reinforce this, particularly against local attacks. The election process is made orderly through the use of [[Timing skew|skew time]], derived from a router's priority, and used to reduce the chance of the [[thundering herd problem]] occurring during the election. The skew time is given by the formula {{math|(256 − ''Priority'') / 256}} (expressed in milliseconds).

Secondary/standby router utilization can be improved by load sharing.{{Ref RFC|5798|rsection=4.2}}