The Priority System

With the analysis of the priorities, VRRP controls the order in which the physical routers take over the function of the master in a VRRP group. VRRP only considers the failure of an entire device to be a trigger for the backup event.

Since numerous devices have more than one WAN interface, the VRRP application in LCOS interprets not only the failure of a device as a trigger for the backup event, but also interruptions to the data connection or the unavailability of a remote site. In order to enable the backup behavior of the devices and the formation of backup chains, every virtual router is assigned two priorities: a main and a backup priority.

The main priority is used (propagated into the network) as long as the device is in normal operating condition (i.e. the remote site for the standard connection is still available).
The backup priority is propagated when the device is in backup mode (i.e. the backup delay has expired and the connection could not be reestablished).
If '0' is set as the backup priority, the router will not send any signals until the end of the backup event, i.e. the device is not available to the VRRP router group when the remote site is not available.

Since VRRP only knows "priorities" and does not differentiate between main or backup priority, it simply analyzes the priority that is currently being propagated by the device. The device with the currently highest priority is considered to be master.

Note: Normally, priorities are configured so that the main priorities of the devices in a VRRP group are larger than the backup priorities used. However this is a general rule and not a requirement. The main priority of router A can be smaller than the backup priority of another router B. In this case, the backup connection of device B is used before the standard connection of router A in the backup chain.

The assignment of priorities to the various WAN interfaces can be determined from the configuration of the backup connections in the Backup table (under LANconfig in the configuration section Communication > Backup).

The main priority refers to the interface on which the standard connection is configured.
The backup priority refers to the interface on which the backup connection is configured.

A master that has been activated due to the priority status will now attempt to establish a connection if this has been configured as a keep alive connection. If the connection is set up as a normal connection with a hold time, then it will not be established until the next packet is transmitted. If this connection fails, thereby triggering the backup event, then the router will also log off and then propagate itself with its backup priority.