H3C Technologies H3C S10500 Series Switches - Manual (Page 138)

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Tracking a specified interface
The interface tracking function expands the backup functionality of VRRP. It provides backup not only
when the interface to which a VRRP group is assigned fails but also when other interfaces (such as uplink
interfaces) on the router become unavailable.
If the uplink interface of a router in a VRRP group fails, usually the VRRP group cannot be aware of the
uplink interface failure. If the router is the master of the VRRP group, hosts on the LAN are not able to
access external networks because of the uplink failure. This problem can be solved by tracking a
specified uplink interface. If the tracked uplink interface is down or removed, the priority of the master is
automatically decreased by a specified value and a higher priority router in the VRRP group becomes the
master.
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 chapter “Track configuration.”
VRRP application (taking IPv4-based VRRP for 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 35 .
Figure 35 VRRP in master/backup mode