H3C Technologies H3C S7500E Series Switches - Manual (Page 140)

10-7
To enable the VRRP tracking function, configure the routers in the VRRP group to work in
preemptive mode first, so that only the router with the highest priority can always operate as the
master for packet forwarding.
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.
z 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:
z 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.
z Monitor the master on a backup. When the master fails, the backup immediately preempts
as the master to maintain normal communication.
For more information about track entries, see Track Configuration in the High Availability
Configuration Guide.
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 10-5 .