IBM RackSwitch G8000, Application Manual

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RackSwitch G8000: Application Guide
Selecting the Master VRRP Router
Each VRRP router is configured with a priority between 1–254. A bidding process
determines which VRRP router is or becomes the master—the VRRP router with
the highest priority.
The master periodically sends advertisements to an IPv4 multicast address. As long
as the backups receive these advertisements, they remain in the backup state. If a
backup does not receive an advertisement for three advertisement intervals, it
initiates a bidding process to determine which VRRP router has the highest priority
and takes over as master.
If, at any time, a backup determines that it has higher priority than the current
master does, it can preempt the master and become the master itself, unless
configured not to do so. In preemption, the backup assumes the role of master and
begins to send its own advertisements. The current master sees that the backup
has higher priority and will stop functioning as the master.
A backup router can stop receiving advertisements for one of two reasons—the
master can be down, or all communications links between the master and the
backup can be down. If the master has failed, it is clearly desirable for the backup
(or one of the backups, if there is more than one) to become the master.
Note: If the master is healthy but communication between the master and the
backup has failed, there will then be two masters within the virtual router. To
prevent this from happening, configure redundant links to be used between
the switches that form a virtual router.
Failover Methods
With service availability becoming a major concern on the Internet, service
providers are increasingly deploying Internet traffic control devices, such as
application switches, in redundant configurations. N/OS high availability
configurations are based on VRRP. The N/OS implementation of VRRP includes
proprietary extensions.