1-4Working modeA router in a VRRP group works in one of the following two modes:z Non-preemptive modeWhen a router in the VRRP group becomes the master, it stays as the master as long as it operatesnormally, even if a backup is assigned a higher priority later.z Preemptive modeWhen a backup finds its priority higher than that of the master, the backup sends VRRP advertisementsto start a new master election in the VRRP group and becomes the master. Accordingly, the originalmaster becomes a backup.Authentication modeTo avoid being attacked by unauthorized users, VRRP authenticates the received packets by addingauthentication keys into the packets. VRRP provides two authentication modes:z simple: Simple text authenticationA router sending a packet fills an authentication key into the packet, and the router receiving the packetcompares its local authentication key with that of the received packet. If the two authentication keys arethe same, the received VRRP packet is considered real and valid; otherwise, the received packet isconsidered invalid.z md5: MD5 authenticationThe router computes the digest of a packet to be sent using the authentication key and MD5 algorithmand saves the result in the authentication header. The router receiving the packet performs the sameoperation using the authentication key and MD5 algorithm, and compares the result with the content inthe authentication header. If the results are the same, the router receiving the packet considers thepacket an authentic and valid VRRP packet; otherwise, the router considers the packet invalid.On a secure network, you do not need to set the authentication mode.VRRP TimersVRRP timers include VRRP advertisement interval timer and VRRP preemption delay timer.VRRP advertisement interval timerThe master in a VRRP group sends VRRP advertisements periodically to inform the other routers in theVRRP group that it operates properly.You can adjust the interval for sending VRRP advertisements by setting the VRRP advertisementinterval timer. If a backup receives no advertisements in a period three times the interval, the backupregards itself as the master and sends VRRP advertisements to start a new master election.VRRP preemption delay timerTo avoid members in a VRRP group from changing their states frequently and make backups haveenough time to collect information (such as routing information), each backup waits for a period of time(the preemption delay time) after it receives an advertisement with the priority lower than the localpriority, then sends VRRP advertisements to start a new master election in the VRRP group and finallybecomes the master.
