Vrrp Timers - 3Com MSR 50 Series Configuration Manual

1974 C 107: VRRP C
HAPTER

VRRP Timers

ONFIGURATION
Once a backup router finds its priority higher than that of the router acting as the
master, it sends VRRP advertisements to start a new master router election in the
standby group and becomes the master. Accordingly, the original master router
becomes a backup.
Authentication mode
VRRP provides two authentication modes:
simple: Simple text authentication
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You can adopt the simple text authentication mode in a network facing possible
security problems. A router sending a packet fills the authentication key into the
packet, and the router receiving the packet compares its local authentication key
with that of the received packet. If the two authentication keys are the same, the
received VRRP packet is considered real and valid; otherwise, the received packet is
considered an invalid one.
md5: MD5 authentication
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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
whether the packet is valid.
On a secure network, you need not set the authentication mode.
VRRP timers include VRRP advertisement interval timer and VRRP preemption delay
timer.
VRRP advertisement interval timer
The master router in a VRRP standby group sends VRRP advertisements periodically
to inform the other routers 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 router receives no advertisements in three
times the interval, the backup router regards itself as the master router and sends
VRRP advertisements to start a new master router election.
VRRP preemption delay timer
In an unstable network, a backup router may fail to receive the packets from the
master router 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 router 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 router election in a standby
group.