Vrrp Tracking; Principles Of Vrrp - H3C LS-3100-52P-OVS-H3 Operation Manual

Principles of VRRP

With VRRP enabled, the routers decide their respective roles in the VRRP group by priority. The
router with the highest priority becomes the master, and the others are the backups. The master
sends VRRP advertisements periodically to notify the backups that it is working properly, and each
of the backups starts a timer to wait for advertisements from the master.
In preemptive mode, when a backup receives a VRRP advertisement, it compares the priority in
the packet with that of its own. If the priority of the backup is higher, the backup becomes the
master; otherwise, it remains a backup.
In non-preemptive mode, the router in the VRRP group remains as a master or backup as long as
the master does not fail. The backup does not become the master even if the backup is configured
with a higher priority.
If the timer of a backup expires but the backup still does not receive any VRRP advertisement, it
considers that the master fails. In this case, the backup considers itself as the master and sends
VRRP advertisements to start a new master election.

VRRP Tracking

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, normally the VRRP group cannot be aware of the
uplink failure. If the router is the master of the VRRP group, hosts on the LAN are not able to access the
external network because of the uplink failure. You can solve the problem through the function of tracing
a specified interface. In this case, it is the uplink interface. After you configure to monitor the uplink
interface, when the uplink interface goes down, 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 object
By monitoring a Track object, you can:
Monitor the upper link. If there is a fault on the upper link, hosts in the LAN cannot access the
external network through the router. In this case, the state of the monitored Track object changes to
negative and the priority of the router decreases by a specified value. After that, a higher priority
router in the VRRP group becomes the master to maintain the proper communication between the
hosts in the LAN and the external network.
Monitor the master on a backup. If there is a fault on the master, the backup working in the mode
switches to the master immediately to maintain normal communication.
For details of Track object tracking, refer to Track Configuration in the System Volume.
1-6