3Com Switch 4800G 24-Port Configuration Manual page 1079

VRRP Interface Tracking
VRRP Application
(Taking IPv4-Based VRRP
for Example)
master, while the others are the backups. The master sends VRRP
advertisement packets periodically to notify the backups that it is working
properly, and each of the backups starts a timer to wait for advertisement
packets from the master.
In preemption mode, when a backup receives a VRRP advertisement packet, it
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compares the priority in the packet with that of its own. If its priority is higher,
it becomes the master; otherwise, it remains a backup.
In non-preemption mode, the switch in the standby group remains as a master
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or backup as long as the master does not fail. The backup will no become the
master even if the former is configured with a higher priority.
If the timer of a backup expires but the backup still does not receive any VRRP
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advertisement packet, it considers that the master fails. In this case, the backup
switch considers itself as the master switch and sends VRRP advertisements to
start the election process to elect a new master switch for forwarding packets.
The interface tracking function expands the backup functionality of VRRP. It
provides backup not only when the interface to which a standby group is assigned
fails but also when other interfaces on the switch become unavailable. This is
achieved by tracking interfaces. When a monitored interface goes down, the
priority of the switch owning the interface is automatically decreased by a
specified value, allowing a higher priority switch in the standby group to become
the master.
Master/backup
In master/backup mode, only one switch, the master, provides services. When the
master fails, a new master is elected from the original backups. This mode requires
only one standby group, in which each switch holds different priorities and the
one with the highest priority becomes the master, as shown in Figure 322.
Figure 322 VRRP in master/backup mode
10.1.1 .2/24
Host A
10.1.1 .3/24
Host B
10.1.1 .4/24
Host C
At the beginning, Switch A is the master and therefore can forward packets to
external networks, while Switch B and Switch C are backups and are thus in the
state of listening. If Switch A fails, Switch B and Switch C will elect for the new
Virtual IP address:
10.1.1.1/24
Switch A
Master
Switch B
Backup
Network
Switch C
Backup
Introduction to VRRP 1079