H3C Technologies H3C MSR 50 - Manual (Page 67)

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• If the timer of a backup expires but the backup still does not receive any VRRP advertisement, it
considers that the master failed. In this case, the backup considers itself as the master and sends
VRRP advertisements to start a new master election.
• When multiple routers in a VRRP group declare that they are the master because of inconsistent
configuration or network problems, the one with the highest priority becomes the master. If two
routers have the same priority, the one with the highest IP address becomes the master.
• When a backup router receives an advertisement, it compares its priority with the advertised priority.
If its priority is higher, it takes over the master.
VRRP tracking
To enable VRRP tracking, first configure the routers in the VRRP group to operate in preemptive mode, so
that the router with the highest priority always operates as the master for forwarding packets.
1. 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.
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.