1-5z Authentication Data: Authentication key. Currently, this field is used only for simple authenticationand is 0 for any other authentication modes.Principles of VRRPz With VRRP enabled, the routers decide their respective roles in the VRRP group by priority. Therouter with the highest priority becomes the master, and the others are the backups. The mastersends VRRP advertisements periodically to notify the backups that it is working properly, and eachof the backups starts a timer to wait for advertisements from the master.z In preemptive mode, when a backup receives a VRRP advertisement, it compares the priority inthe packet with that of its own. If the priority of the backup is higher, the backup becomes themaster; otherwise, it remains a backup.z In non-preemptive mode, the router in the VRRP group remains as a master or backup as long asthe master does not fail. The backup does not become the master even if the backup is configuredwith a higher priority.z If the timer of a backup expires but the backup still does not receive any VRRP advertisement, itconsiders that the master fails. In this case, the backup considers itself as the master and sendsVRRP advertisements to start a new master election.VRRP TrackingTracking a specified interfaceThe interface tracking function expands the backup functionality of VRRP. It provides backup not onlywhen the interface to which a VRRP group is assigned fails but also when other interfaces (such asuplink interfaces) on the router become unavailable.If the uplink interface of a router in a VRRP group fails, normally the VRRP group cannot be aware of theuplink failure. If the router is the master of the VRRP group, hosts on the LAN are not able to access theexternal network because of the uplink failure. You can solve the problem through the function oftracking a specified interface. In this case, it is the uplink interface. After you configure to monitor theuplink interface, when the uplink interface goes down, the priority of the master is automaticallydecreased by a specified value and a higher priority router in the VRRP group becomes the master.Tracking a Track objectBy monitoring a Track object, you can:z Monitor an uplink and modify the priority of the router according to the state of the uplink. If there isa fault on the uplink, hosts in the LAN cannot access the external network through the router. In thiscase, the state of the monitored Track object changes to negative and the priority of the routerdecreases by a specified value. After that, a higher priority router in the VRRP group becomes themaster to maintain the proper communication between the hosts in the LAN and the externalnetwork.z Monitor the master on a backup. If there is a fault on the master, the backup working in the modeswitches to the master immediately to maintain normal communication.
