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Tracking a track entry
By monitoring a track entry, you can:
•
Monitor an uplink and change the priority of the router according to the state of the uplink. If the
uplink fails, hosts in the LAN cannot access external networks through the router. In this case, the
state of the monitored track entry is negative and the priority of the router decreases by a specified
value. Then, a higher priority router in the VRRP group becomes the master to maintain the proper
communication between the hosts in the LAN and external networks.
•
Monitor the master on a backup. When the master fails, the backup immediately preempts as the
master to maintain normal communication.
NOTE:
For more information about track entries, see the
High Availability Configuration Guide.
VRRP application
This section take IPv4-based VRRP as an example.
Master/backup
In master/backup mode, only the master forwards packets. When the master fails, a new master is
elected from the backups. This mode requires only one VRRP group, in which each router holds a different
priority and the one with the highest priority becomes the master, as shown in
.
Figure 33
VRRP in master/backup mode
Assume that Router A is the master and therefore can forward packets to external networks, and that
Router B and Router C are backups and are therefore in the listening state. If Router A fails, Router B and
Router C elect a new master to forward packets to hosts on the LAN.
Load sharing
More than one VRRP group can be created on an interface of a router to allow the router to be the master
of one VRRP group but a backup of another at the same time.
In load sharing mode, multiple routers provide services simultaneously. This mode requires two or more
VRRP groups, each of which comprises a master and one or more backups. The master roles in the VRRP
groups are assumed by different routers, as shown in
.
