3Com Switch 4800G 24-Port Configuration Manual page 1076

1076 C 87: VRRP C
HAPTER ONFIGURATION
md5: MD5 authentication
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You can adopt MD5 authentication in a network facing severe security problems.
The switch encrypts a packet to be sent using the authentication key and MD5
algorithm and saves the encrypted packet in the authentication header. The switch
receiving the packet uses the authentication key to decrypt the packet and checks
whether the packet is valid.
On a secure network, you need not set the authentication mode.
VRRP Timers VRRP timers include VRRP advertisement interval timer and VRRP preemption delay
timer.
VRRP advertisement interval timer
The master switch in a VRRP standby group sends VRRP advertisements
periodically to inform the other switches in the standby group that it operates
properly.
You can adjust the interval of sending VRRP advertisements by setting the VRRP
advertisement interval timer. If a backup switch receives no advertisements in three
times the interval, the backup switch regards itself as the master switch and sends
VRRP advertisements to start a new master switch election.
VRRP preemption delay timer
In an unstable network, a backup switch may fail to receive the packets from the
master switch due to network congestion, thus causing the members in the group
to change their states frequently. This problem can be addressed through setting
the VRRP preemption delay timer.
With the VRRP preemption delay timer set, if a backup switch receives no
advertisement in three times the advertisement interval and then in preemption
delay, it considers that the master fails. In this case, it regards itself as the master
and sends VRRP advertisements to start a new master switch election in a standby
group.
Format of VRRP Packets VRRP uses multicast packets. The switch 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.