Vrrp Timers; Format Of Vrrp Packets - HP 4800G Series Configuration Manual

You can adopt MD5 authentication in a network facing severe security problems. The router encrypts a
packet to be sent using the authentication key and MD5 algorithm and saves the encrypted packet in
the authentication header. The router receiving the packet uses the authentication key to decrypt the
packet and checks the validity of the packet.
On a secure network, you do not need to set the authentication mode.

VRRP Timers

VRRP timers include VRRP advertisement interval timer and VRRP preemption delay timer.
VRRP advertisement interval timer
The master in a VRRP group sends VRRP advertisements periodically to inform the other routers in the
VRRP group that it operates properly.
You can adjust the interval for sending VRRP advertisements by setting the VRRP advertisement
interval timer. If a backup receives no advertisements in a period three times the interval, the backup
regards itself as the master and sends VRRP advertisements to start a new master election.
VRRP preemption delay timer
In an unstable network, a backup can fail to receive the packets from the master due to network
congestion and thus the members in the group change their states frequently. Set the VRRP
preemption delay timer to address the problem.
With the VRRP preemption delay timer set, if a backup receives no advertisement in a period three
times the advertisement interval and then the preemption delay, it considers that the master fails. In this
case, the backup regards itself as the master and sends VRRP advertisements to start a new master
election in the VRRP group.

Format of VRRP Packets

VRRP uses multicast packets. The router acting as the master sends VRRP packets periodically to
declare its existence. VRRP packets are also used for checking the parameters of the virtual router and
electing the master.
IPv4-based VRRP packet format
Figure 1-3 Format of IPv4-based VRRP packet
As shown in Figure
Version: Version number of the protocol, 2 for VRRPv2.
1-3, an IPv4-based VRRP packet consists of the following fields:
1-4