R2511-HP MSR Router Series High Availability Configuration Guide(V5)

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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.
2. Tracking a track entry
By monitoring a track entry, you can do the following:
{ Monitor an uplink and change the priority of the router according to the uplink state.
If the uplink fails, hosts in the LAN cannot access external networks through the router. 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 takes over to maintain normal communication.
For more information about track entries, see "Configuring Track."
VRRP application (taking IPv4-based VRRP for example)
1. 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.
Figure 22 VRRP in master/backup mode
Assume that Router A is acting as the master to forward packets to external networks, and Router
B and Router C are backups in listening state. When Router A fails, Router B and Router C elect a
new master to forward packets for hosts on the LAN.
2. Load sharing