Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 612)

Backup preempt configuration
By default, a Backup that has a higher priority than another Backup that has become the Master can
preempt the Master, and take over the role of Master. If you want to prevent this behavior, disable
preemption.
Preemption applies only to Backups and takes effect only when the Master has failed and a Backup
has assumed ownership of the VRID. The feature prevents a Backup with a higher priority from taking
over as Master from another Backup that has a lower priority but has already become the Master of
the VRID.
Preemption is especially useful for preventing flapping in situations where there are multiple Backups
and a Backup with a lower priority than another Backup has assumed ownership, because the Backup
with the higher priority was unavailable when ownership changed.
If you enable the non-preempt mode (thus disabling the preemption feature) on all the Backups, the
Backup that becomes the Master following the disappearance of the Master continues to be the
Master. The new Master is not preempted.
NOTE
In VRRP, regardless of the setting for the preempt parameter, the Owner always becomes the Master
again when it comes back online.
To disable preemption on a Backup, enter commands such as the following.
device Router1(config)#interface ethernet 1/6
device Router1(config-if-1/6)#ip vrrp vrid 1
device Router1(config-if-1/6-vrid-1)#non-preempt-mode
Syntax: [no] non-preempt-mode
The syntax is the same for VRRP and VRRP-E.
Changing the timer scale
NOTE
Changing the timer scale is supported for IPv4 VRRP v2, IPv4 VRRP-E v2, and IPv6 VRRP-E v3. It is
not supported for IPv6 VRRP v3.
To achieve sub-second failover times, you can shorten the duration of all scale timers for VSRP,
VRRP, and VRRP-E by adjusting the timer scale. The timerscale is a value used by the software to
calculate the timers. By default, the scale value is 1. If you increase the timer scale, each timer’s value
is divided by the scale value. Using the timer scale to adjust timer values enables you to easily change
all the timers while preserving the ratios among their values.
Time scale values TABLE 126
Timer Timer scale Timer value
Hello interval 1 1 second
2 0.5 seconds
Dead interval 1 3 seconds
Backup preempt configuration
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