HSRP Timers can be adjusted to tune the performance of HSRP on the
Distribution devices, thereby increasing their resilience and reliability in
routing packets off the local VLAN.
Sub-second Failover
The HSRP hello and holdtime can be set to
millisecond values so that HSRP failover occurs in less than 1 second. For
example:
Switch(config-if)#standby 1 timers msec 200
msec 750
Preempt Time Aligned with Router Boot Time
Preempt is an
important feature of HSRP which allows the primary router to re-assume the
active role when it comes back online after a failure or maintenance event.
Preemption is a desired behavior as it forces a predictable routing path for
the VLAN during normal operations and ensures that the Layer 3 forwarding path
for a VLAN parallels the Layer 2 STP forwarding path whenever possible.
When a preempting devices is rebooted, HSRP preempt communication should not
begin until the distribution switch has established full connectivity to the
rest of the network. This allows the routing protocol convergence to occur more
quickly once the preferred router in an active state. To accomplish this,
measure the system boot time and set the HSRP preempt delay to a value 50
percent greater than the boot time. This ensures that the primary distribution
switch establishes full connectivity to the network before HSRP communication
occurs.
For example, if the boot time for the distribution device is 120
seconds, the preempt configuration would appear as follows:
standby 1 preempt
standby 1 preempt delay minimum 180