The Access Point will not fail over or reboot until it has missed 5 consecutive polls to the Wireless Controller.
The AP divides the poll timeout by 5 and sends a poll message on that interval. If the AP poll timeout is set to 15, then the Poll Interval is every 3 seconds.
With Fast Failover is enabled, the poll interval is multipled by 3. So, if the AP poll timeout is 15, it will poll every 3 seconds (15/5) but with fast failover enabled, it is multiplied by 3 and it will be a poll interval of 9.
Ex. 2 – Poll timeout is 20. 20/5 = 4 x 3 = Real poll interval is 12 seconds
If Fast Failover is enabled and a controller determines that it can’t talk to its Availability Pair the controller forces the AP to cut the poll timeout set by the administrator in ½. The AP then sends poll messages more frequently. It still needs to lose 5 consecutive messages before it will failover.
There is failover algorithm that requires the AP Poll timeout to be 1.5-2 times the setting for Fast Failover.
The default settings for Fast Failover and AP Poll Timeout are:
Fast Failover = 8 seconds
AP Poll Timeout = 15
Typically, as wireless deployments grow larger, denser, and clients increase, it is advised to increase the AP Poll interval. If AP Poll timeouts are seen, it is recommended to increase the Fast Failover time to 10 or 20, and the AP Poll timeout to a value of 20 to 30.